[sbcl.git] / src / compiler / srctran.lisp

;;;; This file contains macro-like source transformations which
;;;; convert uses of certain functions into the canonical form desired
;;;; within the compiler. ### and other IR1 transforms and stuff.

;;;; This software is part of the SBCL system. See the README file for
;;;; more information.
;;;;
;;;; This software is derived from the CMU CL system, which was
;;;; written at Carnegie Mellon University and released into the
;;;; public domain. The software is in the public domain and is
;;;; provided with absolutely no warranty. See the COPYING and CREDITS
;;;; files for more information.

(in-package "SB!C")

;;; Convert into an IF so that IF optimizations will eliminate redundant
;;; negations.
(def-source-transform not (x) `(if ,x nil t))
(def-source-transform null (x) `(if ,x nil t))

;;; ENDP is just NULL with a LIST assertion. The assertion will be
;;; optimized away when SAFETY optimization is low; hopefully that
;;; is consistent with ANSI's "should return an error".
(def-source-transform endp (x) `(null (the list ,x)))

;;; We turn IDENTITY into PROG1 so that it is obvious that it just
;;; returns the first value of its argument. Ditto for VALUES with one
;;; arg.
(def-source-transform identity (x) `(prog1 ,x))
(def-source-transform values (x) `(prog1 ,x))

;;; Bind the values and make a closure that returns them.
(def-source-transform constantly (value)
  (let ((rest (gensym "CONSTANTLY-REST-")))
    `(lambda (&rest ,rest)
       (declare (ignore ,rest))
       ,value)))

;;; If the function has a known number of arguments, then return a
;;; lambda with the appropriate fixed number of args. If the
;;; destination is a FUNCALL, then do the &REST APPLY thing, and let
;;; MV optimization figure things out.
(deftransform complement ((fun) * * :node node :when :both)
  "open code"
  (multiple-value-bind (min max)
      (function-type-nargs (continuation-type fun))
    (cond
     ((and min (eql min max))
      (let ((dums (make-gensym-list min)))
        `#'(lambda ,dums (not (funcall fun ,@dums)))))
     ((let* ((cont (node-cont node))
             (dest (continuation-dest cont)))
        (and (combination-p dest)
             (eq (combination-fun dest) cont)))
      '#'(lambda (&rest args)
           (not (apply fun args))))
     (t
      (give-up-ir1-transform
       "The function doesn't have a fixed argument count.")))))
\f
;;;; list hackery

;;; Translate CxxR into CAR/CDR combos.

(defun source-transform-cxr (form)
  (if (or (byte-compiling) (/= (length form) 2))
      (values nil t)
      (let ((name (symbol-name (car form))))
        (do ((i (- (length name) 2) (1- i))
             (res (cadr form)
                  `(,(ecase (char name i)
                       (#\A 'car)
                       (#\D 'cdr))
                    ,res)))
            ((zerop i) res)))))

(do ((i 2 (1+ i))
     (b '(1 0) (cons i b)))
    ((= i 5))
  (dotimes (j (ash 1 i))
    (setf (info :function :source-transform
                (intern (format nil "C~{~:[A~;D~]~}R"
                                (mapcar #'(lambda (x) (logbitp x j)) b))))
          #'source-transform-cxr)))

;;; Turn FIRST..FOURTH and REST into the obvious synonym, assuming
;;; whatever is right for them is right for us. FIFTH..TENTH turn into
;;; Nth, which can be expanded into a CAR/CDR later on if policy
;;; favors it.
(def-source-transform first (x) `(car ,x))
(def-source-transform rest (x) `(cdr ,x))
(def-source-transform second (x) `(cadr ,x))
(def-source-transform third (x) `(caddr ,x))
(def-source-transform fourth (x) `(cadddr ,x))
(def-source-transform fifth (x) `(nth 4 ,x))
(def-source-transform sixth (x) `(nth 5 ,x))
(def-source-transform seventh (x) `(nth 6 ,x))
(def-source-transform eighth (x) `(nth 7 ,x))
(def-source-transform ninth (x) `(nth 8 ,x))
(def-source-transform tenth (x) `(nth 9 ,x))

;;; Translate RPLACx to LET and SETF.
(def-source-transform rplaca (x y)
  (once-only ((n-x x))
    `(progn
       (setf (car ,n-x) ,y)
       ,n-x)))
(def-source-transform rplacd (x y)
  (once-only ((n-x x))
    `(progn
       (setf (cdr ,n-x) ,y)
       ,n-x)))

(def-source-transform nth (n l) `(car (nthcdr ,n ,l)))

(defvar *default-nthcdr-open-code-limit* 6)
(defvar *extreme-nthcdr-open-code-limit* 20)

(deftransform nthcdr ((n l) (unsigned-byte t) * :node node)
  "convert NTHCDR to CAxxR"
  (unless (constant-continuation-p n)
    (give-up-ir1-transform))
  (let ((n (continuation-value n)))
    (when (> n
             (if (policy node (and (= speed 3) (= space 0)))
                 *extreme-nthcdr-open-code-limit*
                 *default-nthcdr-open-code-limit*))
      (give-up-ir1-transform))

    (labels ((frob (n)
               (if (zerop n)
                   'l
                   `(cdr ,(frob (1- n))))))
      (frob n))))
\f
;;;; arithmetic and numerology

(def-source-transform plusp (x) `(> ,x 0))
(def-source-transform minusp (x) `(< ,x 0))
(def-source-transform zerop (x) `(= ,x 0))

(def-source-transform 1+ (x) `(+ ,x 1))
(def-source-transform 1- (x) `(- ,x 1))

(def-source-transform oddp (x) `(not (zerop (logand ,x 1))))
(def-source-transform evenp (x) `(zerop (logand ,x 1)))

;;; Note that all the integer division functions are available for
;;; inline expansion.

;;; FIXME: DEF-FROB instead of FROB
(macrolet ((frob (fun)
             `(def-source-transform ,fun (x &optional (y nil y-p))
                (declare (ignore y))
                (if y-p
                    (values nil t)
                    `(,',fun ,x 1)))))
  (frob truncate)
  (frob round)
  #!+propagate-float-type
  (frob floor)
  #!+propagate-float-type
  (frob ceiling))

(def-source-transform lognand (x y) `(lognot (logand ,x ,y)))
(def-source-transform lognor (x y) `(lognot (logior ,x ,y)))
(def-source-transform logandc1 (x y) `(logand (lognot ,x) ,y))
(def-source-transform logandc2 (x y) `(logand ,x (lognot ,y)))
(def-source-transform logorc1 (x y) `(logior (lognot ,x) ,y))
(def-source-transform logorc2 (x y) `(logior ,x (lognot ,y)))
(def-source-transform logtest (x y) `(not (zerop (logand ,x ,y))))
(def-source-transform logbitp (index integer)
  `(not (zerop (logand (ash 1 ,index) ,integer))))
(def-source-transform byte (size position) `(cons ,size ,position))
(def-source-transform byte-size (spec) `(car ,spec))
(def-source-transform byte-position (spec) `(cdr ,spec))
(def-source-transform ldb-test (bytespec integer)
  `(not (zerop (mask-field ,bytespec ,integer))))

;;; With the ratio and complex accessors, we pick off the "identity"
;;; case, and use a primitive to handle the cell access case.
(def-source-transform numerator (num)
  (once-only ((n-num `(the rational ,num)))
    `(if (ratiop ,n-num)
         (%numerator ,n-num)
         ,n-num)))
(def-source-transform denominator (num)
  (once-only ((n-num `(the rational ,num)))
    `(if (ratiop ,n-num)
         (%denominator ,n-num)
         1)))
\f
;;;; interval arithmetic for computing bounds
;;;;
;;;; This is a set of routines for operating on intervals. It
;;;; implements a simple interval arithmetic package. Although SBCL
;;;; has an interval type in NUMERIC-TYPE, we choose to use our own
;;;; for two reasons:
;;;;
;;;;   1. This package is simpler than NUMERIC-TYPE.
;;;;
;;;;   2. It makes debugging much easier because you can just strip
;;;;   out these routines and test them independently of SBCL. (This is a
;;;;   big win!)
;;;;
;;;; One disadvantage is a probable increase in consing because we
;;;; have to create these new interval structures even though
;;;; numeric-type has everything we want to know. Reason 2 wins for
;;;; now.

#-sb-xc-host ;(CROSS-FLOAT-INFINITY-KLUDGE, see base-target-features.lisp-expr)
(progn
#!+propagate-float-type
(progn

;;; The basic interval type. It can handle open and closed intervals.
;;; A bound is open if it is a list containing a number, just like
;;; Lisp says. NIL means unbounded.
(defstruct (interval (:constructor %make-interval)
                     (:copier nil))
  low high)

(defun make-interval (&key low high)
  (labels ((normalize-bound (val)
             (cond ((and (floatp val)
                         (float-infinity-p val))
                    ;; Handle infinities.
                    nil)
                   ((or (numberp val)
                        (eq val nil))
                    ;; Handle any closed bounds.
                    val)
                   ((listp val)
                    ;; We have an open bound. Normalize the numeric
                    ;; bound. If the normalized bound is still a number
                    ;; (not nil), keep the bound open. Otherwise, the
                    ;; bound is really unbounded, so drop the openness.
                    (let ((new-val (normalize-bound (first val))))
                      (when new-val
                        ;; The bound exists, so keep it open still.
                        (list new-val))))
                   (t
                    (error "Unknown bound type in make-interval!")))))
    (%make-interval :low (normalize-bound low)
                    :high (normalize-bound high))))

#!-sb-fluid (declaim (inline bound-value set-bound))

;;; Extract the numeric value of a bound. Return NIL, if X is NIL.
(defun bound-value (x)
  (if (consp x) (car x) x))

;;; Given a number X, create a form suitable as a bound for an
;;; interval. Make the bound open if OPEN-P is T. NIL remains NIL.
(defun set-bound (x open-p)
  (if (and x open-p) (list x) x))

;;; Apply the function F to a bound X. If X is an open bound, then
;;; the result will be open. IF X is NIL, the result is NIL.
(defun bound-func (f x)
  (and x
       (with-float-traps-masked (:underflow :overflow :inexact :divide-by-zero)
         ;; With these traps masked, we might get things like infinity
         ;; or negative infinity returned. Check for this and return
         ;; NIL to indicate unbounded.
         (let ((y (funcall f (bound-value x))))
           (if (and (floatp y)
                    (float-infinity-p y))
               nil
               (set-bound (funcall f (bound-value x)) (consp x)))))))

;;; Apply a binary operator OP to two bounds X and Y. The result is
;;; NIL if either is NIL. Otherwise bound is computed and the result
;;; is open if either X or Y is open.
;;;
;;; FIXME: only used in this file, not needed in target runtime
(defmacro bound-binop (op x y)
  `(and ,x ,y
       (with-float-traps-masked (:underflow :overflow :inexact :divide-by-zero)
         (set-bound (,op (bound-value ,x)
                         (bound-value ,y))
                    (or (consp ,x) (consp ,y))))))

;;; Convert a numeric-type object to an interval object.
(defun numeric-type->interval (x)
  (declare (type numeric-type x))
  (make-interval :low (numeric-type-low x)
                 :high (numeric-type-high x)))

(defun copy-interval-limit (limit)
  (if (numberp limit)
      limit
      (copy-list limit)))

(defun copy-interval (x)
  (declare (type interval x))
  (make-interval :low (copy-interval-limit (interval-low x))
                 :high (copy-interval-limit (interval-high x))))

;;; Given a point P contained in the interval X, split X into two
;;; interval at the point P. If CLOSE-LOWER is T, then the left
;;; interval contains P. If CLOSE-UPPER is T, the right interval
;;; contains P. You can specify both to be T or NIL.
(defun interval-split (p x &optional close-lower close-upper)
  (declare (type number p)
           (type interval x))
  (list (make-interval :low (copy-interval-limit (interval-low x))
                       :high (if close-lower p (list p)))
        (make-interval :low (if close-upper (list p) p)
                       :high (copy-interval-limit (interval-high x)))))

;;; Return the closure of the interval. That is, convert open bounds
;;; to closed bounds.
(defun interval-closure (x)
  (declare (type interval x))
  (make-interval :low (bound-value (interval-low x))
                 :high (bound-value (interval-high x))))

(defun signed-zero->= (x y)
  (declare (real x y))
  (or (> x y)
      (and (= x y)
           (>= (float-sign (float x))
               (float-sign (float y))))))

;;; For an interval X, if X >= POINT, return '+. If X <= POINT, return
;;; '-. Otherwise return NIL.
#+nil
(defun interval-range-info (x &optional (point 0))
  (declare (type interval x))
  (let ((lo (interval-low x))
        (hi (interval-high x)))
    (cond ((and lo (signed-zero->= (bound-value lo) point))
           '+)
          ((and hi (signed-zero->= point (bound-value hi)))
           '-)
          (t
           nil))))
(defun interval-range-info (x &optional (point 0))
  (declare (type interval x))
  (labels ((signed->= (x y)
             (if (and (zerop x) (zerop y) (floatp x) (floatp y))
                 (>= (float-sign x) (float-sign y))
                 (>= x y))))
    (let ((lo (interval-low x))
          (hi (interval-high x)))
      (cond ((and lo (signed->= (bound-value lo) point))
             '+)
            ((and hi (signed->= point (bound-value hi)))
             '-)
            (t
             nil)))))

;;; Test to see whether the interval X is bounded. HOW determines the
;;; test, and should be either ABOVE, BELOW, or BOTH.
(defun interval-bounded-p (x how)
  (declare (type interval x))
  (ecase how
    ('above
     (interval-high x))
    ('below
     (interval-low x))
    ('both
     (and (interval-low x) (interval-high x)))))

;;; signed zero comparison functions. Use these functions if we need
;;; to distinguish between signed zeroes.
(defun signed-zero-< (x y)
  (declare (real x y))
  (or (< x y)
      (and (= x y)
           (< (float-sign (float x))
              (float-sign (float y))))))
(defun signed-zero-> (x y)
  (declare (real x y))
  (or (> x y)
      (and (= x y)
           (> (float-sign (float x))
              (float-sign (float y))))))
(defun signed-zero-= (x y)
  (declare (real x y))
  (and (= x y)
       (= (float-sign (float x))
          (float-sign (float y)))))
(defun signed-zero-<= (x y)
  (declare (real x y))
  (or (< x y)
      (and (= x y)
           (<= (float-sign (float x))
               (float-sign (float y))))))

;;; See whether the interval X contains the number P, taking into
;;; account that the interval might not be closed.
(defun interval-contains-p (p x)
  (declare (type number p)
           (type interval x))
  ;; Does the interval X contain the number P?  This would be a lot
  ;; easier if all intervals were closed!
  (let ((lo (interval-low x))
        (hi (interval-high x)))
    (cond ((and lo hi)
           ;; The interval is bounded
           (if (and (signed-zero-<= (bound-value lo) p)
                    (signed-zero-<= p (bound-value hi)))
               ;; P is definitely in the closure of the interval.
               ;; We just need to check the end points now.
               (cond ((signed-zero-= p (bound-value lo))
                      (numberp lo))
                     ((signed-zero-= p (bound-value hi))
                      (numberp hi))
                     (t t))
               nil))
          (hi
           ;; Interval with upper bound
           (if (signed-zero-< p (bound-value hi))
               t
               (and (numberp hi) (signed-zero-= p hi))))
          (lo
           ;; Interval with lower bound
           (if (signed-zero-> p (bound-value lo))
               t
               (and (numberp lo) (signed-zero-= p lo))))
          (t
           ;; Interval with no bounds
           t))))

;;; Determine whether two intervals X and Y intersect. Return T if so.
;;; If CLOSED-INTERVALS-P is T, the treat the intervals as if they
;;; were closed. Otherwise the intervals are treated as they are.
;;;
;;; Thus if X = [0, 1) and Y = (1, 2), then they do not intersect
;;; because no element in X is in Y. However, if CLOSED-INTERVALS-P
;;; is T, then they do intersect because we use the closure of X = [0,
;;; 1] and Y = [1, 2] to determine intersection.
(defun interval-intersect-p (x y &optional closed-intervals-p)
  (declare (type interval x y))
  (multiple-value-bind (intersect diff)
      (interval-intersection/difference (if closed-intervals-p
                                            (interval-closure x)
                                            x)
                                        (if closed-intervals-p
                                            (interval-closure y)
                                            y))
    (declare (ignore diff))
    intersect))

;;; Are the two intervals adjacent?  That is, is there a number
;;; between the two intervals that is not an element of either
;;; interval?  If so, they are not adjacent. For example [0, 1) and
;;; [1, 2] are adjacent but [0, 1) and (1, 2] are not because 1 lies
;;; between both intervals.
(defun interval-adjacent-p (x y)
  (declare (type interval x y))
  (flet ((adjacent (lo hi)
           ;; Check to see whether lo and hi are adjacent. If either is
           ;; nil, they can't be adjacent.
           (when (and lo hi (= (bound-value lo) (bound-value hi)))
             ;; The bounds are equal. They are adjacent if one of
             ;; them is closed (a number). If both are open (consp),
             ;; then there is a number that lies between them.
             (or (numberp lo) (numberp hi)))))
    (or (adjacent (interval-low y) (interval-high x))
        (adjacent (interval-low x) (interval-high y)))))

;;; Compute the intersection and difference between two intervals.
;;; Two values are returned: the intersection and the difference.
;;;
;;; Let the two intervals be X and Y, and let I and D be the two
;;; values returned by this function. Then I = X intersect Y. If I
;;; is NIL (the empty set), then D is X union Y, represented as the
;;; list of X and Y. If I is not the empty set, then D is (X union Y)
;;; - I, which is a list of two intervals.
;;;
;;; For example, let X = [1,5] and Y = [-1,3). Then I = [1,3) and D =
;;; [-1,1) union [3,5], which is returned as a list of two intervals.
(defun interval-intersection/difference (x y)
  (declare (type interval x y))
  (let ((x-lo (interval-low x))
        (x-hi (interval-high x))
        (y-lo (interval-low y))
        (y-hi (interval-high y)))
    (labels
        ((opposite-bound (p)
           ;; If p is an open bound, make it closed. If p is a closed
           ;; bound, make it open.
           (if (listp p)
               (first p)
               (list p)))
         (test-number (p int)
           ;; Test whether P is in the interval.
           (when (interval-contains-p (bound-value p)
                                      (interval-closure int))
             (let ((lo (interval-low int))
                   (hi (interval-high int)))
               ;; Check for endpoints.
               (cond ((and lo (= (bound-value p) (bound-value lo)))
                      (not (and (consp p) (numberp lo))))
                     ((and hi (= (bound-value p) (bound-value hi)))
                      (not (and (numberp p) (consp hi))))
                     (t t)))))
         (test-lower-bound (p int)
           ;; P is a lower bound of an interval.
           (if p
               (test-number p int)
               (not (interval-bounded-p int 'below))))
         (test-upper-bound (p int)
           ;; P is an upper bound of an interval.
           (if p
               (test-number p int)
               (not (interval-bounded-p int 'above)))))
      (let ((x-lo-in-y (test-lower-bound x-lo y))
            (x-hi-in-y (test-upper-bound x-hi y))
            (y-lo-in-x (test-lower-bound y-lo x))
            (y-hi-in-x (test-upper-bound y-hi x)))
        (cond ((or x-lo-in-y x-hi-in-y y-lo-in-x y-hi-in-x)
               ;; Intervals intersect. Let's compute the intersection
               ;; and the difference.
               (multiple-value-bind (lo left-lo left-hi)
                   (cond (x-lo-in-y (values x-lo y-lo (opposite-bound x-lo)))
                         (y-lo-in-x (values y-lo x-lo (opposite-bound y-lo))))
                 (multiple-value-bind (hi right-lo right-hi)
                     (cond (x-hi-in-y
                            (values x-hi (opposite-bound x-hi) y-hi))
                           (y-hi-in-x
                            (values y-hi (opposite-bound y-hi) x-hi)))
                   (values (make-interval :low lo :high hi)
                           (list (make-interval :low left-lo
                                                :high left-hi)
                                 (make-interval :low right-lo
                                                :high right-hi))))))
              (t
               (values nil (list x y))))))))

;;; If intervals X and Y intersect, return a new interval that is the
;;; union of the two. If they do not intersect, return NIL.
(defun interval-merge-pair (x y)
  (declare (type interval x y))
  ;; If x and y intersect or are adjacent, create the union.
  ;; Otherwise return nil
  (when (or (interval-intersect-p x y)
            (interval-adjacent-p x y))
    (flet ((select-bound (x1 x2 min-op max-op)
             (let ((x1-val (bound-value x1))
                   (x2-val (bound-value x2)))
               (cond ((and x1 x2)
                      ;; Both bounds are finite. Select the right one.
                      (cond ((funcall min-op x1-val x2-val)
                             ;; x1 is definitely better.
                             x1)
                            ((funcall max-op x1-val x2-val)
                             ;; x2 is definitely better.
                             x2)
                            (t
                             ;; Bounds are equal. Select either
                             ;; value and make it open only if
                             ;; both were open.
                             (set-bound x1-val (and (consp x1) (consp x2))))))
                     (t
                      ;; At least one bound is not finite. The
                      ;; non-finite bound always wins.
                      nil)))))
      (let* ((x-lo (copy-interval-limit (interval-low x)))
             (x-hi (copy-interval-limit (interval-high x)))
             (y-lo (copy-interval-limit (interval-low y)))
             (y-hi (copy-interval-limit (interval-high y))))
        (make-interval :low (select-bound x-lo y-lo #'< #'>)
                       :high (select-bound x-hi y-hi #'> #'<))))))

;;; basic arithmetic operations on intervals. We probably should do
;;; true interval arithmetic here, but it's complicated because we
;;; have float and integer types and bounds can be open or closed.

;;; the negative of an interval
(defun interval-neg (x)
  (declare (type interval x))
  (make-interval :low (bound-func #'- (interval-high x))
                 :high (bound-func #'- (interval-low x))))

;;; Add two intervals.
(defun interval-add (x y)
  (declare (type interval x y))
  (make-interval :low (bound-binop + (interval-low x) (interval-low y))
                 :high (bound-binop + (interval-high x) (interval-high y))))

;;; Subtract two intervals.
(defun interval-sub (x y)
  (declare (type interval x y))
  (make-interval :low (bound-binop - (interval-low x) (interval-high y))
                 :high (bound-binop - (interval-high x) (interval-low y))))

;;; Multiply two intervals.
(defun interval-mul (x y)
  (declare (type interval x y))
  (flet ((bound-mul (x y)
           (cond ((or (null x) (null y))
                  ;; Multiply by infinity is infinity
                  nil)
                 ((or (and (numberp x) (zerop x))
                      (and (numberp y) (zerop y)))
                  ;; Multiply by closed zero is special. The result
                  ;; is always a closed bound. But don't replace this
                  ;; with zero; we want the multiplication to produce
                  ;; the correct signed zero, if needed.
                  (* (bound-value x) (bound-value y)))
                 ((or (and (floatp x) (float-infinity-p x))
                      (and (floatp y) (float-infinity-p y)))
                  ;; Infinity times anything is infinity
                  nil)
                 (t
                  ;; General multiply. The result is open if either is open.
                  (bound-binop * x y)))))
    (let ((x-range (interval-range-info x))
          (y-range (interval-range-info y)))
      (cond ((null x-range)
             ;; Split x into two and multiply each separately
             (destructuring-bind (x- x+) (interval-split 0 x t t)
               (interval-merge-pair (interval-mul x- y)
                                    (interval-mul x+ y))))
            ((null y-range)
             ;; Split y into two and multiply each separately
             (destructuring-bind (y- y+) (interval-split 0 y t t)
               (interval-merge-pair (interval-mul x y-)
                                    (interval-mul x y+))))
            ((eq x-range '-)
             (interval-neg (interval-mul (interval-neg x) y)))
            ((eq y-range '-)
             (interval-neg (interval-mul x (interval-neg y))))
            ((and (eq x-range '+) (eq y-range '+))
             ;; If we are here, X and Y are both positive
             (make-interval :low (bound-mul (interval-low x) (interval-low y))
                            :high (bound-mul (interval-high x) (interval-high y))))
            (t
             (error "This shouldn't happen!"))))))

;;; Divide two intervals.
(defun interval-div (top bot)
  (declare (type interval top bot))
  (flet ((bound-div (x y y-low-p)
           ;; Compute x/y
           (cond ((null y)
                  ;; Divide by infinity means result is 0. However,
                  ;; we need to watch out for the sign of the result,
                  ;; to correctly handle signed zeros. We also need
                  ;; to watch out for positive or negative infinity.
                  (if (floatp (bound-value x))
                      (if y-low-p
                          (- (float-sign (bound-value x) 0.0))
                          (float-sign (bound-value x) 0.0))
                      0))
                 ((zerop (bound-value y))
                  ;; Divide by zero means result is infinity
                  nil)
                 ((and (numberp x) (zerop x))
                  ;; Zero divided by anything is zero.
                  x)
                 (t
                  (bound-binop / x y)))))
    (let ((top-range (interval-range-info top))
          (bot-range (interval-range-info bot)))
      (cond ((null bot-range)
             ;; The denominator contains zero, so anything goes!
             (make-interval :low nil :high nil))
            ((eq bot-range '-)
             ;; Denominator is negative so flip the sign, compute the
             ;; result, and flip it back.
             (interval-neg (interval-div top (interval-neg bot))))
            ((null top-range)
             ;; Split top into two positive and negative parts, and
             ;; divide each separately
             (destructuring-bind (top- top+) (interval-split 0 top t t)
               (interval-merge-pair (interval-div top- bot)
                                    (interval-div top+ bot))))
            ((eq top-range '-)
             ;; Top is negative so flip the sign, divide, and flip the
             ;; sign of the result.
             (interval-neg (interval-div (interval-neg top) bot)))
            ((and (eq top-range '+) (eq bot-range '+))
             ;; The easy case
             (make-interval :low (bound-div (interval-low top) (interval-high bot) t)
                            :high (bound-div (interval-high top) (interval-low bot) nil)))
            (t
             (error "This shouldn't happen!"))))))

;;; Apply the function F to the interval X. If X = [a, b], then the
;;; result is [f(a), f(b)]. It is up to the user to make sure the
;;; result makes sense. It will if F is monotonic increasing (or
;;; non-decreasing).
(defun interval-func (f x)
  (declare (type interval x))
  (let ((lo (bound-func f (interval-low x)))
        (hi (bound-func f (interval-high x))))
    (make-interval :low lo :high hi)))

;;; Return T if X < Y. That is every number in the interval X is
;;; always less than any number in the interval Y.
(defun interval-< (x y)
  (declare (type interval x y))
  ;; X < Y only if X is bounded above, Y is bounded below, and they
  ;; don't overlap.
  (when (and (interval-bounded-p x 'above)
             (interval-bounded-p y 'below))
    ;; Intervals are bounded in the appropriate way. Make sure they
    ;; don't overlap.
    (let ((left (interval-high x))
          (right (interval-low y)))
      (cond ((> (bound-value left)
                (bound-value right))
             ;; Definitely overlap so result is NIL
             nil)
            ((< (bound-value left)
                (bound-value right))
             ;; Definitely don't touch, so result is T
             t)
            (t
             ;; Limits are equal. Check for open or closed bounds.
             ;; Don't overlap if one or the other are open.
             (or (consp left) (consp right)))))))

;;; Return T if X >= Y. That is, every number in the interval X is
;;; always greater than any number in the interval Y.
(defun interval->= (x y)
  (declare (type interval x y))
  ;; X >= Y if lower bound of X >= upper bound of Y
  (when (and (interval-bounded-p x 'below)
             (interval-bounded-p y 'above))
    (>= (bound-value (interval-low x)) (bound-value (interval-high y)))))

;;; Return an interval that is the absolute value of X. Thus, if
;;; X = [-1 10], the result is [0, 10].
(defun interval-abs (x)
  (declare (type interval x))
  (case (interval-range-info x)
    ('+
     (copy-interval x))
    ('-
     (interval-neg x))
    (t
     (destructuring-bind (x- x+) (interval-split 0 x t t)
       (interval-merge-pair (interval-neg x-) x+)))))

;;; Compute the square of an interval.
(defun interval-sqr (x)
  (declare (type interval x))
  (interval-func #'(lambda (x) (* x x))
                 (interval-abs x)))
)) ; end PROGN's
\f
;;;; numeric DERIVE-TYPE methods

;;; a utility for defining derive-type methods of integer operations. If
;;; the types of both X and Y are integer types, then we compute a new
;;; integer type with bounds determined Fun when applied to X and Y.
;;; Otherwise, we use Numeric-Contagion.
(defun derive-integer-type (x y fun)
  (declare (type continuation x y) (type function fun))
  (let ((x (continuation-type x))
        (y (continuation-type y)))
    (if (and (numeric-type-p x) (numeric-type-p y)
             (eq (numeric-type-class x) 'integer)
             (eq (numeric-type-class y) 'integer)
             (eq (numeric-type-complexp x) :real)
             (eq (numeric-type-complexp y) :real))
        (multiple-value-bind (low high) (funcall fun x y)
          (make-numeric-type :class 'integer
                             :complexp :real
                             :low low
                             :high high))
        (numeric-contagion x y))))

#!+(or propagate-float-type propagate-fun-type)
(progn

;;; simple utility to flatten a list
(defun flatten-list (x)
  (labels ((flatten-helper (x r);; 'r' is the stuff to the 'right'.
             (cond ((null x) r)
                   ((atom x)
                    (cons x r))
                   (t (flatten-helper (car x)
                                      (flatten-helper (cdr x) r))))))
    (flatten-helper x nil)))

;;; Take some type of continuation and massage it so that we get a
;;; list of the constituent types. If ARG is *EMPTY-TYPE*, return NIL
;;; to indicate failure.
(defun prepare-arg-for-derive-type (arg)
  (flet ((listify (arg)
           (typecase arg
             (numeric-type
              (list arg))
             (union-type
              (union-type-types arg))
             (t
              (list arg)))))
    (unless (eq arg *empty-type*)
      ;; Make sure all args are some type of numeric-type. For member
      ;; types, convert the list of members into a union of equivalent
      ;; single-element member-type's.
      (let ((new-args nil))
        (dolist (arg (listify arg))
          (if (member-type-p arg)
              ;; Run down the list of members and convert to a list of
              ;; member types.
              (dolist (member (member-type-members arg))
                (push (if (numberp member)
                          (make-member-type :members (list member))
                          *empty-type*)
                      new-args))
              (push arg new-args)))
        (unless (member *empty-type* new-args)
          new-args)))))

;;; Convert from the standard type convention for which -0.0 and 0.0
;;; and equal to an intermediate convention for which they are
;;; considered different which is more natural for some of the
;;; optimisers.
#!-negative-zero-is-not-zero
(defun convert-numeric-type (type)
  (declare (type numeric-type type))
  ;;; Only convert real float interval delimiters types.
  (if (eq (numeric-type-complexp type) :real)
      (let* ((lo (numeric-type-low type))
             (lo-val (bound-value lo))
             (lo-float-zero-p (and lo (floatp lo-val) (= lo-val 0.0)))
             (hi (numeric-type-high type))
             (hi-val (bound-value hi))
             (hi-float-zero-p (and hi (floatp hi-val) (= hi-val 0.0))))
        (if (or lo-float-zero-p hi-float-zero-p)
            (make-numeric-type
             :class (numeric-type-class type)
             :format (numeric-type-format type)
             :complexp :real
             :low (if lo-float-zero-p
                      (if (consp lo)
                          (list (float 0.0 lo-val))
                          (float -0.0 lo-val))
                      lo)
             :high (if hi-float-zero-p
                       (if (consp hi)
                           (list (float -0.0 hi-val))
                           (float 0.0 hi-val))
                       hi))
            type))
      ;; Not real float.
      type))

;;; Convert back from the intermediate convention for which -0.0 and
;;; 0.0 are considered different to the standard type convention for
;;; which and equal.
#!-negative-zero-is-not-zero
(defun convert-back-numeric-type (type)
  (declare (type numeric-type type))
  ;;; Only convert real float interval delimiters types.
  (if (eq (numeric-type-complexp type) :real)
      (let* ((lo (numeric-type-low type))
             (lo-val (bound-value lo))
             (lo-float-zero-p
              (and lo (floatp lo-val) (= lo-val 0.0)
                   (float-sign lo-val)))
             (hi (numeric-type-high type))
             (hi-val (bound-value hi))
             (hi-float-zero-p
              (and hi (floatp hi-val) (= hi-val 0.0)
                   (float-sign hi-val))))
        (cond
          ;; (float +0.0 +0.0) => (member 0.0)
          ;; (float -0.0 -0.0) => (member -0.0)
          ((and lo-float-zero-p hi-float-zero-p)
           ;; shouldn't have exclusive bounds here..
           (aver (and (not (consp lo)) (not (consp hi))))
           (if (= lo-float-zero-p hi-float-zero-p)
               ;; (float +0.0 +0.0) => (member 0.0)
               ;; (float -0.0 -0.0) => (member -0.0)
               (specifier-type `(member ,lo-val))
               ;; (float -0.0 +0.0) => (float 0.0 0.0)
               ;; (float +0.0 -0.0) => (float 0.0 0.0)
               (make-numeric-type :class (numeric-type-class type)
                                  :format (numeric-type-format type)
                                  :complexp :real
                                  :low hi-val
                                  :high hi-val)))
          (lo-float-zero-p
           (cond
             ;; (float -0.0 x) => (float 0.0 x)
             ((and (not (consp lo)) (minusp lo-float-zero-p))
              (make-numeric-type :class (numeric-type-class type)
                                 :format (numeric-type-format type)
                                 :complexp :real
                                 :low (float 0.0 lo-val)
                                 :high hi))
             ;; (float (+0.0) x) => (float (0.0) x)
             ((and (consp lo) (plusp lo-float-zero-p))
              (make-numeric-type :class (numeric-type-class type)
                                 :format (numeric-type-format type)
                                 :complexp :real
                                 :low (list (float 0.0 lo-val))
                                 :high hi))
             (t
              ;; (float +0.0 x) => (or (member 0.0) (float (0.0) x))
              ;; (float (-0.0) x) => (or (member 0.0) (float (0.0) x))
              (list (make-member-type :members (list (float 0.0 lo-val)))
                    (make-numeric-type :class (numeric-type-class type)
                                       :format (numeric-type-format type)
                                       :complexp :real
                                       :low (list (float 0.0 lo-val))
                                       :high hi)))))
          (hi-float-zero-p
           (cond
             ;; (float x +0.0) => (float x 0.0)
             ((and (not (consp hi)) (plusp hi-float-zero-p))
              (make-numeric-type :class (numeric-type-class type)
                                 :format (numeric-type-format type)
                                 :complexp :real
                                 :low lo
                                 :high (float 0.0 hi-val)))
             ;; (float x (-0.0)) => (float x (0.0))
             ((and (consp hi) (minusp hi-float-zero-p))
              (make-numeric-type :class (numeric-type-class type)
                                 :format (numeric-type-format type)
                                 :complexp :real
                                 :low lo
                                 :high (list (float 0.0 hi-val))))
             (t
              ;; (float x (+0.0)) => (or (member -0.0) (float x (0.0)))
              ;; (float x -0.0) => (or (member -0.0) (float x (0.0)))
              (list (make-member-type :members (list (float -0.0 hi-val)))
                    (make-numeric-type :class (numeric-type-class type)
                                       :format (numeric-type-format type)
                                       :complexp :real
                                       :low lo
                                       :high (list (float 0.0 hi-val)))))))
          (t
           type)))
      ;; Not real float.
      type))

;;; Convert back a possible list of numeric types.
#!-negative-zero-is-not-zero
(defun convert-back-numeric-type-list (type-list)
  (typecase type-list
    (list
     (let ((results '()))
       (dolist (type type-list)
         (if (numeric-type-p type)
             (let ((result (convert-back-numeric-type type)))
               (if (listp result)
                   (setf results (append results result))
                   (push result results)))
             (push type results)))
       results))
    (numeric-type
     (convert-back-numeric-type type-list))
    (union-type
     (convert-back-numeric-type-list (union-type-types type-list)))
    (t
     type-list)))

;;; FIXME: MAKE-CANONICAL-UNION-TYPE and CONVERT-MEMBER-TYPE probably
;;; belong in the kernel's type logic, invoked always, instead of in
;;; the compiler, invoked only during some type optimizations.

;;; Take a list of types and return a canonical type specifier,
;;; combining any MEMBER types together. If both positive and negative
;;; MEMBER types are present they are converted to a float type.
;;; XXX This would be far simpler if the type-union methods could handle
;;; member/number unions.
(defun make-canonical-union-type (type-list)
  (let ((members '())
        (misc-types '()))
    (dolist (type type-list)
      (if (member-type-p type)
          (setf members (union members (member-type-members type)))
          (push type misc-types)))
    #!+long-float
    (when (null (set-difference '(-0l0 0l0) members))
      #!-negative-zero-is-not-zero
      (push (specifier-type '(long-float 0l0 0l0)) misc-types)
      #!+negative-zero-is-not-zero
      (push (specifier-type '(long-float -0l0 0l0)) misc-types)
      (setf members (set-difference members '(-0l0 0l0))))
    (when (null (set-difference '(-0d0 0d0) members))
      #!-negative-zero-is-not-zero
      (push (specifier-type '(double-float 0d0 0d0)) misc-types)
      #!+negative-zero-is-not-zero
      (push (specifier-type '(double-float -0d0 0d0)) misc-types)
      (setf members (set-difference members '(-0d0 0d0))))
    (when (null (set-difference '(-0f0 0f0) members))
      #!-negative-zero-is-not-zero
      (push (specifier-type '(single-float 0f0 0f0)) misc-types)
      #!+negative-zero-is-not-zero
      (push (specifier-type '(single-float -0f0 0f0)) misc-types)
      (setf members (set-difference members '(-0f0 0f0))))
    (if members
        (apply #'type-union (make-member-type :members members) misc-types)
        (apply #'type-union misc-types))))

;;; Convert a member type with a single member to a numeric type.
(defun convert-member-type (arg)
  (let* ((members (member-type-members arg))
         (member (first members))
         (member-type (type-of member)))
    (aver (not (rest members)))
    (specifier-type `(,(if (subtypep member-type 'integer)
                           'integer
                           member-type)
                      ,member ,member))))

;;; This is used in defoptimizers for computing the resulting type of
;;; a function.
;;;
;;; Given the continuation ARG, derive the resulting type using the
;;; DERIVE-FCN. DERIVE-FCN takes exactly one argument which is some
;;; "atomic" continuation type like numeric-type or member-type
;;; (containing just one element). It should return the resulting
;;; type, which can be a list of types.
;;;
;;; For the case of member types, if a member-fcn is given it is
;;; called to compute the result otherwise the member type is first
;;; converted to a numeric type and the derive-fcn is call.
(defun one-arg-derive-type (arg derive-fcn member-fcn
                                &optional (convert-type t))
  (declare (type function derive-fcn)
           (type (or null function) member-fcn)
           #!+negative-zero-is-not-zero (ignore convert-type))
  (let ((arg-list (prepare-arg-for-derive-type (continuation-type arg))))
    (when arg-list
      (flet ((deriver (x)
               (typecase x
                 (member-type
                  (if member-fcn
                      (with-float-traps-masked
                          (:underflow :overflow :divide-by-zero)
                        (make-member-type
                         :members (list
                                   (funcall member-fcn
                                            (first (member-type-members x))))))
                      ;; Otherwise convert to a numeric type.
                      (let ((result-type-list
                             (funcall derive-fcn (convert-member-type x))))
                        #!-negative-zero-is-not-zero
                        (if convert-type
                            (convert-back-numeric-type-list result-type-list)
                            result-type-list)
                        #!+negative-zero-is-not-zero
                        result-type-list)))
                 (numeric-type
                  #!-negative-zero-is-not-zero
                  (if convert-type
                      (convert-back-numeric-type-list
                       (funcall derive-fcn (convert-numeric-type x)))
                      (funcall derive-fcn x))
                  #!+negative-zero-is-not-zero
                  (funcall derive-fcn x))
                 (t
                  *universal-type*))))
        ;; Run down the list of args and derive the type of each one,
        ;; saving all of the results in a list.
        (let ((results nil))
          (dolist (arg arg-list)
            (let ((result (deriver arg)))
              (if (listp result)
                  (setf results (append results result))
                  (push result results))))
          (if (rest results)
              (make-canonical-union-type results)
              (first results)))))))

;;; Same as ONE-ARG-DERIVE-TYPE, except we assume the function takes
;;; two arguments. DERIVE-FCN takes 3 args in this case: the two
;;; original args and a third which is T to indicate if the two args
;;; really represent the same continuation. This is useful for
;;; deriving the type of things like (* x x), which should always be
;;; positive. If we didn't do this, we wouldn't be able to tell.
(defun two-arg-derive-type (arg1 arg2 derive-fcn fcn
                                 &optional (convert-type t))
  #!+negative-zero-is-not-zero
  (declare (ignore convert-type))
  (flet (#!-negative-zero-is-not-zero
         (deriver (x y same-arg)
           (cond ((and (member-type-p x) (member-type-p y))
                  (let* ((x (first (member-type-members x)))
                         (y (first (member-type-members y)))
                         (result (with-float-traps-masked
                                     (:underflow :overflow :divide-by-zero
                                      :invalid)
                                   (funcall fcn x y))))
                    (cond ((null result))
                          ((and (floatp result) (float-nan-p result))
                           (make-numeric-type
                            :class 'float
                            :format (type-of result)
                            :complexp :real))
                          (t
                           (make-member-type :members (list result))))))
                 ((and (member-type-p x) (numeric-type-p y))
                  (let* ((x (convert-member-type x))
                         (y (if convert-type (convert-numeric-type y) y))
                         (result (funcall derive-fcn x y same-arg)))
                    (if convert-type
                        (convert-back-numeric-type-list result)
                        result)))
                 ((and (numeric-type-p x) (member-type-p y))
                  (let* ((x (if convert-type (convert-numeric-type x) x))
                         (y (convert-member-type y))
                         (result (funcall derive-fcn x y same-arg)))
                    (if convert-type
                        (convert-back-numeric-type-list result)
                        result)))
                 ((and (numeric-type-p x) (numeric-type-p y))
                  (let* ((x (if convert-type (convert-numeric-type x) x))
                         (y (if convert-type (convert-numeric-type y) y))
                         (result (funcall derive-fcn x y same-arg)))
                    (if convert-type
                        (convert-back-numeric-type-list result)
                        result)))
                 (t
                  *universal-type*)))
         #!+negative-zero-is-not-zero
         (deriver (x y same-arg)
           (cond ((and (member-type-p x) (member-type-p y))
                  (let* ((x (first (member-type-members x)))
                         (y (first (member-type-members y)))
                         (result (with-float-traps-masked
                                     (:underflow :overflow :divide-by-zero)
                                   (funcall fcn x y))))
                    (if result
                        (make-member-type :members (list result)))))
                 ((and (member-type-p x) (numeric-type-p y))
                  (let ((x (convert-member-type x)))
                    (funcall derive-fcn x y same-arg)))
                 ((and (numeric-type-p x) (member-type-p y))
                  (let ((y (convert-member-type y)))
                    (funcall derive-fcn x y same-arg)))
                 ((and (numeric-type-p x) (numeric-type-p y))
                  (funcall derive-fcn x y same-arg))
                 (t
                  *universal-type*))))
    (let ((same-arg (same-leaf-ref-p arg1 arg2))
          (a1 (prepare-arg-for-derive-type (continuation-type arg1)))
          (a2 (prepare-arg-for-derive-type (continuation-type arg2))))
      (when (and a1 a2)
        (let ((results nil))
          (if same-arg
              ;; Since the args are the same continuation, just run
              ;; down the lists.
              (dolist (x a1)
                (let ((result (deriver x x same-arg)))
                  (if (listp result)
                      (setf results (append results result))
                      (push result results))))
              ;; Try all pairwise combinations.
              (dolist (x a1)
                (dolist (y a2)
                  (let ((result (or (deriver x y same-arg)
                                    (numeric-contagion x y))))
                    (if (listp result)
                        (setf results (append results result))
                        (push result results))))))
          (if (rest results)
              (make-canonical-union-type results)
              (first results)))))))

) ; PROGN
\f
#!-propagate-float-type
(progn
(defoptimizer (+ derive-type) ((x y))
  (derive-integer-type
   x y
   #'(lambda (x y)
       (flet ((frob (x y)
                (if (and x y)
                    (+ x y)
                    nil)))
         (values (frob (numeric-type-low x) (numeric-type-low y))
                 (frob (numeric-type-high x) (numeric-type-high y)))))))

(defoptimizer (- derive-type) ((x y))
  (derive-integer-type
   x y
   #'(lambda (x y)
       (flet ((frob (x y)
                (if (and x y)
                    (- x y)
                    nil)))
         (values (frob (numeric-type-low x) (numeric-type-high y))
                 (frob (numeric-type-high x) (numeric-type-low y)))))))

(defoptimizer (* derive-type) ((x y))
  (derive-integer-type
   x y
   #'(lambda (x y)
       (let ((x-low (numeric-type-low x))
             (x-high (numeric-type-high x))
             (y-low (numeric-type-low y))
             (y-high (numeric-type-high y)))
         (cond ((not (and x-low y-low))
                (values nil nil))
               ((or (minusp x-low) (minusp y-low))
                (if (and x-high y-high)
                    (let ((max (* (max (abs x-low) (abs x-high))
                                  (max (abs y-low) (abs y-high)))))
                      (values (- max) max))
                    (values nil nil)))
               (t
                (values (* x-low y-low)
                        (if (and x-high y-high)
                            (* x-high y-high)
                            nil))))))))

(defoptimizer (/ derive-type) ((x y))
  (numeric-contagion (continuation-type x) (continuation-type y)))

) ; PROGN

#!+propagate-float-type
(progn
(defun +-derive-type-aux (x y same-arg)
  (if (and (numeric-type-real-p x)
           (numeric-type-real-p y))
      (let ((result
             (if same-arg
                 (let ((x-int (numeric-type->interval x)))
                   (interval-add x-int x-int))
                 (interval-add (numeric-type->interval x)
                               (numeric-type->interval y))))
            (result-type (numeric-contagion x y)))
        ;; If the result type is a float, we need to be sure to coerce
        ;; the bounds into the correct type.
        (when (eq (numeric-type-class result-type) 'float)
          (setf result (interval-func
                        #'(lambda (x)
                            (coerce x (or (numeric-type-format result-type)
                                          'float)))
                        result)))
        (make-numeric-type
         :class (if (and (eq (numeric-type-class x) 'integer)
                         (eq (numeric-type-class y) 'integer))
                    ;; The sum of integers is always an integer
                    'integer
                    (numeric-type-class result-type))
         :format (numeric-type-format result-type)
         :low (interval-low result)
         :high (interval-high result)))
      ;; General contagion
      (numeric-contagion x y)))

(defoptimizer (+ derive-type) ((x y))
  (two-arg-derive-type x y #'+-derive-type-aux #'+))

(defun --derive-type-aux (x y same-arg)
  (if (and (numeric-type-real-p x)
           (numeric-type-real-p y))
      (let ((result
             ;; (- X X) is always 0.
             (if same-arg
                 (make-interval :low 0 :high 0)
                 (interval-sub (numeric-type->interval x)
                               (numeric-type->interval y))))
            (result-type (numeric-contagion x y)))
        ;; If the result type is a float, we need to be sure to coerce
        ;; the bounds into the correct type.
        (when (eq (numeric-type-class result-type) 'float)
          (setf result (interval-func
                        #'(lambda (x)
                            (coerce x (or (numeric-type-format result-type)
                                          'float)))
                        result)))
        (make-numeric-type
         :class (if (and (eq (numeric-type-class x) 'integer)
                         (eq (numeric-type-class y) 'integer))
                    ;; The difference of integers is always an integer.
                    'integer
                    (numeric-type-class result-type))
         :format (numeric-type-format result-type)
         :low (interval-low result)
         :high (interval-high result)))
      ;; general contagion
      (numeric-contagion x y)))

(defoptimizer (- derive-type) ((x y))
  (two-arg-derive-type x y #'--derive-type-aux #'-))

(defun *-derive-type-aux (x y same-arg)
  (if (and (numeric-type-real-p x)
           (numeric-type-real-p y))
      (let ((result
             ;; (* x x) is always positive, so take care to do it
             ;; right.
             (if same-arg
                 (interval-sqr (numeric-type->interval x))
                 (interval-mul (numeric-type->interval x)
                               (numeric-type->interval y))))
            (result-type (numeric-contagion x y)))
        ;; If the result type is a float, we need to be sure to coerce
        ;; the bounds into the correct type.
        (when (eq (numeric-type-class result-type) 'float)
          (setf result (interval-func
                        #'(lambda (x)
                            (coerce x (or (numeric-type-format result-type)
                                          'float)))
                        result)))
        (make-numeric-type
         :class (if (and (eq (numeric-type-class x) 'integer)
                         (eq (numeric-type-class y) 'integer))
                    ;; The product of integers is always an integer.
                    'integer
                    (numeric-type-class result-type))
         :format (numeric-type-format result-type)
         :low (interval-low result)
         :high (interval-high result)))
      (numeric-contagion x y)))

(defoptimizer (* derive-type) ((x y))
  (two-arg-derive-type x y #'*-derive-type-aux #'*))

(defun /-derive-type-aux (x y same-arg)
  (if (and (numeric-type-real-p x)
           (numeric-type-real-p y))
      (let ((result
             ;; (/ X X) is always 1, except if X can contain 0. In
             ;; that case, we shouldn't optimize the division away
             ;; because we want 0/0 to signal an error.
             (if (and same-arg
                      (not (interval-contains-p
                            0 (interval-closure (numeric-type->interval y)))))
                 (make-interval :low 1 :high 1)
                 (interval-div (numeric-type->interval x)
                               (numeric-type->interval y))))
            (result-type (numeric-contagion x y)))
        ;; If the result type is a float, we need to be sure to coerce
        ;; the bounds into the correct type.
        (when (eq (numeric-type-class result-type) 'float)
          (setf result (interval-func
                        #'(lambda (x)
                            (coerce x (or (numeric-type-format result-type)
                                          'float)))
                        result)))
        (make-numeric-type :class (numeric-type-class result-type)
                           :format (numeric-type-format result-type)
                           :low (interval-low result)
                           :high (interval-high result)))
      (numeric-contagion x y)))

(defoptimizer (/ derive-type) ((x y))
  (two-arg-derive-type x y #'/-derive-type-aux #'/))

) ; PROGN


;;; KLUDGE: All this ASH optimization is suppressed under CMU CL
;;; because as of version 2.4.6 for Debian, CMU CL blows up on (ASH
;;; 1000000000 -100000000000) (i.e. ASH of two bignums yielding zero)
;;; and it's hard to avoid that calculation in here.
#-(and cmu sb-xc-host)
(progn
#!-propagate-fun-type
(defoptimizer (ash derive-type) ((n shift))
  ;; Large resulting bounds are easy to generate but are not
  ;; particularly useful, so an open outer bound is returned for a
  ;; shift greater than 64 - the largest word size of any of the ports.
  ;; Large negative shifts are also problematic as the ASH
  ;; implementation only accepts shifts greater than
  ;; MOST-NEGATIVE-FIXNUM. These issues are handled by two local
  ;; functions:
  ;;   ASH-OUTER: Perform the shift when within an acceptable range,
  ;;     otherwise return an open bound.
  ;;   ASH-INNER: Perform the shift when within range, limited to a
  ;;     maximum of 64, otherwise returns the inner limit.
  ;;
  ;; FIXME: The magic number 64 should be given a mnemonic name as a
  ;; symbolic constant -- perhaps +MAX-REGISTER-SIZE+. And perhaps is
  ;; should become an architecture-specific SB!VM:+MAX-REGISTER-SIZE+
  ;; instead of trying to have a single magic number which covers
  ;; all possible ports.
  (flet ((ash-outer (n s)
            (when (and (fixnump s)
                       (<= s 64)
                       (> s sb!vm:*target-most-negative-fixnum*))
              (ash n s)))
          (ash-inner (n s)
            (if (and (fixnump s)
                     (> s sb!vm:*target-most-negative-fixnum*))
              (ash n (min s 64))
              (if (minusp n) -1 0))))
     (or (let ((n-type (continuation-type n)))
           (when (numeric-type-p n-type)
             (let ((n-low (numeric-type-low n-type))
                   (n-high (numeric-type-high n-type)))
               (if (constant-continuation-p shift)
                 (let ((shift (continuation-value shift)))
                   (make-numeric-type :class 'integer
                                      :complexp :real
                                      :low (when n-low (ash n-low shift))
                                      :high (when n-high (ash n-high shift))))
                 (let ((s-type (continuation-type shift)))
                   (when (numeric-type-p s-type)
                     (let* ((s-low (numeric-type-low s-type))
                            (s-high (numeric-type-high s-type))
                            (low-slot (when n-low
                                        (if (minusp n-low)
                                            (ash-outer n-low s-high)
                                            (ash-inner n-low s-low))))
                            (high-slot (when n-high
                                         (if (minusp n-high)
                                             (ash-inner n-high s-low)
                                             (ash-outer n-high s-high)))))
                       (make-numeric-type :class 'integer
                                          :complexp :real
                                          :low low-slot
                                          :high high-slot))))))))
         *universal-type*))
  (or (let ((n-type (continuation-type n)))
        (when (numeric-type-p n-type)
          (let ((n-low (numeric-type-low n-type))
                (n-high (numeric-type-high n-type)))
            (if (constant-continuation-p shift)
                (let ((shift (continuation-value shift)))
                  (make-numeric-type :class 'integer
                                     :complexp :real
                                     :low (when n-low (ash n-low shift))
                                     :high (when n-high (ash n-high shift))))
                (let ((s-type (continuation-type shift)))
                  (when (numeric-type-p s-type)
                    (let ((s-low (numeric-type-low s-type))
                          (s-high (numeric-type-high s-type)))
                      (if (and s-low s-high (<= s-low 64) (<= s-high 64))
                          (make-numeric-type :class 'integer
                                             :complexp :real
                                             :low (when n-low
                                                    (min (ash n-low s-high)
                                                         (ash n-low s-low)))
                                             :high (when n-high
                                                     (max (ash n-high s-high)
                                                          (ash n-high s-low))))
                          (make-numeric-type :class 'integer
                                             :complexp :real)))))))))
      *universal-type*))

#!+propagate-fun-type
(defun ash-derive-type-aux (n-type shift same-arg)
  (declare (ignore same-arg))
  (flet ((ash-outer (n s)
           (when (and (fixnump s)
                      (<= s 64)
                      (> s sb!vm:*target-most-negative-fixnum*))
             (ash n s)))
         ;; KLUDGE: The bare 64's here should be related to
         ;; symbolic machine word size values somehow.

         (ash-inner (n s)
           (if (and (fixnump s)
                    (> s sb!vm:*target-most-negative-fixnum*))
             (ash n (min s 64))
             (if (minusp n) -1 0))))
    (or (and (csubtypep n-type (specifier-type 'integer))
             (csubtypep shift (specifier-type 'integer))
             (let ((n-low (numeric-type-low n-type))
                   (n-high (numeric-type-high n-type))
                   (s-low (numeric-type-low shift))
                   (s-high (numeric-type-high shift)))
               (make-numeric-type :class 'integer  :complexp :real
                                  :low (when n-low
                                         (if (minusp n-low)
                                           (ash-outer n-low s-high)
                                           (ash-inner n-low s-low)))
                                  :high (when n-high
                                          (if (minusp n-high)
                                            (ash-inner n-high s-low)
                                            (ash-outer n-high s-high))))))
        *universal-type*)))

#!+propagate-fun-type
(defoptimizer (ash derive-type) ((n shift))
  (two-arg-derive-type n shift #'ash-derive-type-aux #'ash))
) ; PROGN

#!-propagate-float-type
(macrolet ((frob (fun)
             `#'(lambda (type type2)
                  (declare (ignore type2))
                  (let ((lo (numeric-type-low type))
                        (hi (numeric-type-high type)))
                    (values (if hi (,fun hi) nil) (if lo (,fun lo) nil))))))

  (defoptimizer (%negate derive-type) ((num))
    (derive-integer-type num num (frob -)))

  (defoptimizer (lognot derive-type) ((int))
    (derive-integer-type int int (frob lognot))))

#!+propagate-float-type
(defoptimizer (lognot derive-type) ((int))
  (derive-integer-type int int
                       (lambda (type type2)
                         (declare (ignore type2))
                         (let ((lo (numeric-type-low type))
                               (hi (numeric-type-high type)))
                           (values (if hi (lognot hi) nil)
                                   (if lo (lognot lo) nil)
                                   (numeric-type-class type)
                                   (numeric-type-format type))))))

#!+propagate-float-type
(defoptimizer (%negate derive-type) ((num))
  (flet ((negate-bound (b)
           (set-bound (- (bound-value b)) (consp b))))
    (one-arg-derive-type num
                         (lambda (type)
                           (let ((lo (numeric-type-low type))
                                 (hi (numeric-type-high type))
                                 (result (copy-numeric-type type)))
                             (setf (numeric-type-low result)
                                   (if hi (negate-bound hi) nil))
                             (setf (numeric-type-high result)
                                   (if lo (negate-bound lo) nil))
                             result))
                         #'-)))

#!-propagate-float-type
(defoptimizer (abs derive-type) ((num))
  (let ((type (continuation-type num)))
    (if (and (numeric-type-p type)
             (eq (numeric-type-class type) 'integer)
             (eq (numeric-type-complexp type) :real))
        (let ((lo (numeric-type-low type))
              (hi (numeric-type-high type)))
          (make-numeric-type :class 'integer :complexp :real
                             :low (cond ((and hi (minusp hi))
                                         (abs hi))
                                        (lo
                                         (max 0 lo))
                                        (t
                                         0))
                             :high (if (and hi lo)
                                       (max (abs hi) (abs lo))
                                       nil)))
        (numeric-contagion type type))))

#!+propagate-float-type
(defun abs-derive-type-aux (type)
  (cond ((eq (numeric-type-complexp type) :complex)
         ;; The absolute value of a complex number is always a
         ;; non-negative float.
         (let* ((format (case (numeric-type-class type)
                          ((integer rational) 'single-float)
                          (t (numeric-type-format type))))
                (bound-format (or format 'float)))
           (make-numeric-type :class 'float
                              :format format
                              :complexp :real
                              :low (coerce 0 bound-format)
                              :high nil)))
        (t
         ;; The absolute value of a real number is a non-negative real
         ;; of the same type.
         (let* ((abs-bnd (interval-abs (numeric-type->interval type)))
                (class (numeric-type-class type))
                (format (numeric-type-format type))
                (bound-type (or format class 'real)))
           (make-numeric-type
            :class class
            :format format
            :complexp :real
            :low (coerce-numeric-bound (interval-low abs-bnd) bound-type)
            :high (coerce-numeric-bound
                   (interval-high abs-bnd) bound-type))))))

#!+propagate-float-type
(defoptimizer (abs derive-type) ((num))
  (one-arg-derive-type num #'abs-derive-type-aux #'abs))

#!-propagate-float-type
(defoptimizer (truncate derive-type) ((number divisor))
  (let ((number-type (continuation-type number))
        (divisor-type (continuation-type divisor))
        (integer-type (specifier-type 'integer)))
    (if (and (numeric-type-p number-type)
             (csubtypep number-type integer-type)
             (numeric-type-p divisor-type)
             (csubtypep divisor-type integer-type))
        (let ((number-low (numeric-type-low number-type))
              (number-high (numeric-type-high number-type))
              (divisor-low (numeric-type-low divisor-type))
              (divisor-high (numeric-type-high divisor-type)))
          (values-specifier-type
           `(values ,(integer-truncate-derive-type number-low number-high
                                                   divisor-low divisor-high)
                    ,(integer-rem-derive-type number-low number-high
                                              divisor-low divisor-high))))
        *universal-type*)))

#-sb-xc-host ;(CROSS-FLOAT-INFINITY-KLUDGE, see base-target-features.lisp-expr)
(progn
#!+propagate-float-type
(progn

(defun rem-result-type (number-type divisor-type)
  ;; Figure out what the remainder type is. The remainder is an
  ;; integer if both args are integers; a rational if both args are
  ;; rational; and a float otherwise.
  (cond ((and (csubtypep number-type (specifier-type 'integer))
              (csubtypep divisor-type (specifier-type 'integer)))
         'integer)
        ((and (csubtypep number-type (specifier-type 'rational))
              (csubtypep divisor-type (specifier-type 'rational)))
         'rational)
        ((and (csubtypep number-type (specifier-type 'float))
              (csubtypep divisor-type (specifier-type 'float)))
         ;; Both are floats so the result is also a float, of
         ;; the largest type.
         (or (float-format-max (numeric-type-format number-type)
                               (numeric-type-format divisor-type))
             'float))
        ((and (csubtypep number-type (specifier-type 'float))
              (csubtypep divisor-type (specifier-type 'rational)))
         ;; One of the arguments is a float and the other is a
         ;; rational. The remainder is a float of the same
         ;; type.
         (or (numeric-type-format number-type) 'float))
        ((and (csubtypep divisor-type (specifier-type 'float))
              (csubtypep number-type (specifier-type 'rational)))
         ;; One of the arguments is a float and the other is a
         ;; rational. The remainder is a float of the same
         ;; type.
         (or (numeric-type-format divisor-type) 'float))
        (t
         ;; Some unhandled combination. This usually means both args
         ;; are REAL so the result is a REAL.
         'real)))

(defun truncate-derive-type-quot (number-type divisor-type)
  (let* ((rem-type (rem-result-type number-type divisor-type))
         (number-interval (numeric-type->interval number-type))
         (divisor-interval (numeric-type->interval divisor-type)))
    ;;(declare (type (member '(integer rational float)) rem-type))
    ;; We have real numbers now.
    (cond ((eq rem-type 'integer)
           ;; Since the remainder type is INTEGER, both args are
           ;; INTEGERs.
           (let* ((res (integer-truncate-derive-type
                        (interval-low number-interval)
                        (interval-high number-interval)
                        (interval-low divisor-interval)
                        (interval-high divisor-interval))))
             (specifier-type (if (listp res) res 'integer))))
          (t
           (let ((quot (truncate-quotient-bound
                        (interval-div number-interval
                                      divisor-interval))))
             (specifier-type `(integer ,(or (interval-low quot) '*)
                                       ,(or (interval-high quot) '*))))))))

(defun truncate-derive-type-rem (number-type divisor-type)
  (let* ((rem-type (rem-result-type number-type divisor-type))
         (number-interval (numeric-type->interval number-type))
         (divisor-interval (numeric-type->interval divisor-type))
         (rem (truncate-rem-bound number-interval divisor-interval)))
    ;;(declare (type (member '(integer rational float)) rem-type))
    ;; We have real numbers now.
    (cond ((eq rem-type 'integer)
           ;; Since the remainder type is INTEGER, both args are
           ;; INTEGERs.
           (specifier-type `(,rem-type ,(or (interval-low rem) '*)
                                       ,(or (interval-high rem) '*))))
          (t
           (multiple-value-bind (class format)
               (ecase rem-type
                 (integer
                  (values 'integer nil))
                 (rational
                  (values 'rational nil))
                 ((or single-float double-float #!+long-float long-float)
                  (values 'float rem-type))
                 (float
                  (values 'float nil))
                 (real
                  (values nil nil)))
             (when (member rem-type '(float single-float double-float
                                            #!+long-float long-float))
               (setf rem (interval-func #'(lambda (x)
                                            (coerce x rem-type))
                                        rem)))
             (make-numeric-type :class class
                                :format format
                                :low (interval-low rem)
                                :high (interval-high rem)))))))

(defun truncate-derive-type-quot-aux (num div same-arg)
  (declare (ignore same-arg))
  (if (and (numeric-type-real-p num)
           (numeric-type-real-p div))
      (truncate-derive-type-quot num div)
      *empty-type*))

(defun truncate-derive-type-rem-aux (num div same-arg)
  (declare (ignore same-arg))
  (if (and (numeric-type-real-p num)
           (numeric-type-real-p div))
      (truncate-derive-type-rem num div)
      *empty-type*))

(defoptimizer (truncate derive-type) ((number divisor))
  (let ((quot (two-arg-derive-type number divisor
                                   #'truncate-derive-type-quot-aux #'truncate))
        (rem (two-arg-derive-type number divisor
                                  #'truncate-derive-type-rem-aux #'rem)))
    (when (and quot rem)
      (make-values-type :required (list quot rem)))))

(defun ftruncate-derive-type-quot (number-type divisor-type)
  ;; The bounds are the same as for truncate. However, the first
  ;; result is a float of some type. We need to determine what that
  ;; type is. Basically it's the more contagious of the two types.
  (let ((q-type (truncate-derive-type-quot number-type divisor-type))
        (res-type (numeric-contagion number-type divisor-type)))
    (make-numeric-type :class 'float
                       :format (numeric-type-format res-type)
                       :low (numeric-type-low q-type)
                       :high (numeric-type-high q-type))))

(defun ftruncate-derive-type-quot-aux (n d same-arg)
  (declare (ignore same-arg))
  (if (and (numeric-type-real-p n)
           (numeric-type-real-p d))
      (ftruncate-derive-type-quot n d)
      *empty-type*))

(defoptimizer (ftruncate derive-type) ((number divisor))
  (let ((quot
         (two-arg-derive-type number divisor
                              #'ftruncate-derive-type-quot-aux #'ftruncate))
        (rem (two-arg-derive-type number divisor
                                  #'truncate-derive-type-rem-aux #'rem)))
    (when (and quot rem)
      (make-values-type :required (list quot rem)))))

(defun %unary-truncate-derive-type-aux (number)
  (truncate-derive-type-quot number (specifier-type '(integer 1 1))))

(defoptimizer (%unary-truncate derive-type) ((number))
  (one-arg-derive-type number
                       #'%unary-truncate-derive-type-aux
                       #'%unary-truncate))

;;; Define optimizers for FLOOR and CEILING.
(macrolet
    ((frob-opt (name q-name r-name)
       (let ((q-aux (symbolicate q-name "-AUX"))
             (r-aux (symbolicate r-name "-AUX")))
         `(progn
           ;; Compute type of quotient (first) result
           (defun ,q-aux (number-type divisor-type)
             (let* ((number-interval
                     (numeric-type->interval number-type))
                    (divisor-interval
                     (numeric-type->interval divisor-type))
                    (quot (,q-name (interval-div number-interval
                                                 divisor-interval))))
               (specifier-type `(integer ,(or (interval-low quot) '*)
                                         ,(or (interval-high quot) '*)))))
           ;; Compute type of remainder
           (defun ,r-aux (number-type divisor-type)
             (let* ((divisor-interval
                     (numeric-type->interval divisor-type))
                    (rem (,r-name divisor-interval))
                    (result-type (rem-result-type number-type divisor-type)))
               (multiple-value-bind (class format)
                   (ecase result-type
                     (integer
                      (values 'integer nil))
                     (rational
                      (values 'rational nil))
                     ((or single-float double-float #!+long-float long-float)
                      (values 'float result-type))
                     (float
                      (values 'float nil))
                     (real
                      (values nil nil)))
                 (when (member result-type '(float single-float double-float
                                             #!+long-float long-float))
                   ;; Make sure the limits on the interval have
                   ;; the right type.
                   (setf rem (interval-func #'(lambda (x)
                                                (coerce x result-type))
                                            rem)))
                 (make-numeric-type :class class
                                    :format format
                                    :low (interval-low rem)
                                    :high (interval-high rem)))))
           ;; The optimizer itself
           (defoptimizer (,name derive-type) ((number divisor))
             (flet ((derive-q (n d same-arg)
                      (declare (ignore same-arg))
                      (if (and (numeric-type-real-p n)
                               (numeric-type-real-p d))
                          (,q-aux n d)
                          *empty-type*))
                    (derive-r (n d same-arg)
                      (declare (ignore same-arg))
                      (if (and (numeric-type-real-p n)
                               (numeric-type-real-p d))
                          (,r-aux n d)
                          *empty-type*)))
               (let ((quot (two-arg-derive-type
                            number divisor #'derive-q #',name))
                     (rem (two-arg-derive-type
                           number divisor #'derive-r #'mod)))
                 (when (and quot rem)
                   (make-values-type :required (list quot rem))))))
           ))))

  ;; FIXME: DEF-FROB-OPT, not just FROB-OPT
  (frob-opt floor floor-quotient-bound floor-rem-bound)
  (frob-opt ceiling ceiling-quotient-bound ceiling-rem-bound))

;;; Define optimizers for FFLOOR and FCEILING
(macrolet
    ((frob-opt (name q-name r-name)
       (let ((q-aux (symbolicate "F" q-name "-AUX"))
             (r-aux (symbolicate r-name "-AUX")))
         `(progn
           ;; Compute type of quotient (first) result
           (defun ,q-aux (number-type divisor-type)
             (let* ((number-interval
                     (numeric-type->interval number-type))
                    (divisor-interval
                     (numeric-type->interval divisor-type))
                    (quot (,q-name (interval-div number-interval
                                                 divisor-interval)))
                    (res-type (numeric-contagion number-type divisor-type)))
               (make-numeric-type
                :class (numeric-type-class res-type)
                :format (numeric-type-format res-type)
                :low  (interval-low quot)
                :high (interval-high quot))))

           (defoptimizer (,name derive-type) ((number divisor))
             (flet ((derive-q (n d same-arg)
                      (declare (ignore same-arg))
                      (if (and (numeric-type-real-p n)
                               (numeric-type-real-p d))
                          (,q-aux n d)
                          *empty-type*))
                    (derive-r (n d same-arg)
                      (declare (ignore same-arg))
                      (if (and (numeric-type-real-p n)
                               (numeric-type-real-p d))
                          (,r-aux n d)
                          *empty-type*)))
               (let ((quot (two-arg-derive-type
                            number divisor #'derive-q #',name))
                     (rem (two-arg-derive-type
                           number divisor #'derive-r #'mod)))
                 (when (and quot rem)
                   (make-values-type :required (list quot rem))))))))))

  ;; FIXME: DEF-FROB-OPT, not just FROB-OPT
  (frob-opt ffloor floor-quotient-bound floor-rem-bound)
  (frob-opt fceiling ceiling-quotient-bound ceiling-rem-bound))

;;; functions to compute the bounds on the quotient and remainder for
;;; the FLOOR function
(defun floor-quotient-bound (quot)
  ;; Take the floor of the quotient and then massage it into what we
  ;; need.
  (let ((lo (interval-low quot))
        (hi (interval-high quot)))
    ;; Take the floor of the lower bound. The result is always a
    ;; closed lower bound.
    (setf lo (if lo
                 (floor (bound-value lo))
                 nil))
    ;; For the upper bound, we need to be careful
    (setf hi
          (cond ((consp hi)
                 ;; An open bound. We need to be careful here because
                 ;; the floor of '(10.0) is 9, but the floor of
                 ;; 10.0 is 10.
                 (multiple-value-bind (q r) (floor (first hi))
                   (if (zerop r)
                       (1- q)
                       q)))
                (hi
                 ;; A closed bound, so the answer is obvious.
                 (floor hi))
                (t
                 hi)))
    (make-interval :low lo :high hi)))
(defun floor-rem-bound (div)
  ;; The remainder depends only on the divisor. Try to get the
  ;; correct sign for the remainder if we can.
  (case (interval-range-info div)
    (+
     ;; Divisor is always positive.
     (let ((rem (interval-abs div)))
       (setf (interval-low rem) 0)
       (when (and (numberp (interval-high rem))
                  (not (zerop (interval-high rem))))
         ;; The remainder never contains the upper bound. However,
         ;; watch out for the case where the high limit is zero!
         (setf (interval-high rem) (list (interval-high rem))))
       rem))
    (-
     ;; Divisor is always negative
     (let ((rem (interval-neg (interval-abs div))))
       (setf (interval-high rem) 0)
       (when (numberp (interval-low rem))
         ;; The remainder never contains the lower bound.
         (setf (interval-low rem) (list (interval-low rem))))
       rem))
    (otherwise
     ;; The divisor can be positive or negative. All bets off.
     ;; The magnitude of remainder is the maximum value of the
     ;; divisor.
     (let ((limit (bound-value (interval-high (interval-abs div)))))
       ;; The bound never reaches the limit, so make the interval open
       (make-interval :low (if limit
                               (list (- limit))
                               limit)
                      :high (list limit))))))
#| Test cases
(floor-quotient-bound (make-interval :low 0.3 :high 10.3))
=> #S(INTERVAL :LOW 0 :HIGH 10)
(floor-quotient-bound (make-interval :low 0.3 :high '(10.3)))
=> #S(INTERVAL :LOW 0 :HIGH 10)
(floor-quotient-bound (make-interval :low 0.3 :high 10))
=> #S(INTERVAL :LOW 0 :HIGH 10)
(floor-quotient-bound (make-interval :low 0.3 :high '(10)))
=> #S(INTERVAL :LOW 0 :HIGH 9)
(floor-quotient-bound (make-interval :low '(0.3) :high 10.3))
=> #S(INTERVAL :LOW 0 :HIGH 10)
(floor-quotient-bound (make-interval :low '(0.0) :high 10.3))
=> #S(INTERVAL :LOW 0 :HIGH 10)
(floor-quotient-bound (make-interval :low '(-1.3) :high 10.3))
=> #S(INTERVAL :LOW -2 :HIGH 10)
(floor-quotient-bound (make-interval :low '(-1.0) :high 10.3))
=> #S(INTERVAL :LOW -1 :HIGH 10)
(floor-quotient-bound (make-interval :low -1.0 :high 10.3))
=> #S(INTERVAL :LOW -1 :HIGH 10)

(floor-rem-bound (make-interval :low 0.3 :high 10.3))
=> #S(INTERVAL :LOW 0 :HIGH '(10.3))
(floor-rem-bound (make-interval :low 0.3 :high '(10.3)))
=> #S(INTERVAL :LOW 0 :HIGH '(10.3))
(floor-rem-bound (make-interval :low -10 :high -2.3))
#S(INTERVAL :LOW (-10) :HIGH 0)
(floor-rem-bound (make-interval :low 0.3 :high 10))
=> #S(INTERVAL :LOW 0 :HIGH '(10))
(floor-rem-bound (make-interval :low '(-1.3) :high 10.3))
=> #S(INTERVAL :LOW '(-10.3) :HIGH '(10.3))
(floor-rem-bound (make-interval :low '(-20.3) :high 10.3))
=> #S(INTERVAL :LOW (-20.3) :HIGH (20.3))
|#
\f
;;; same functions for CEILING
(defun ceiling-quotient-bound (quot)
  ;; Take the ceiling of the quotient and then massage it into what we
  ;; need.
  (let ((lo (interval-low quot))
        (hi (interval-high quot)))
    ;; Take the ceiling of the upper bound. The result is always a
    ;; closed upper bound.
    (setf hi (if hi
                 (ceiling (bound-value hi))
                 nil))
    ;; For the lower bound, we need to be careful
    (setf lo
          (cond ((consp lo)
                 ;; An open bound. We need to be careful here because
                 ;; the ceiling of '(10.0) is 11, but the ceiling of
                 ;; 10.0 is 10.
                 (multiple-value-bind (q r) (ceiling (first lo))
                   (if (zerop r)
                       (1+ q)
                       q)))
                (lo
                 ;; A closed bound, so the answer is obvious.
                 (ceiling lo))
                (t
                 lo)))
    (make-interval :low lo :high hi)))
(defun ceiling-rem-bound (div)
  ;; The remainder depends only on the divisor. Try to get the
  ;; correct sign for the remainder if we can.

  (case (interval-range-info div)
    (+
     ;; Divisor is always positive. The remainder is negative.
     (let ((rem (interval-neg (interval-abs div))))
       (setf (interval-high rem) 0)
       (when (and (numberp (interval-low rem))
                  (not (zerop (interval-low rem))))
         ;; The remainder never contains the upper bound. However,
         ;; watch out for the case when the upper bound is zero!
         (setf (interval-low rem) (list (interval-low rem))))
       rem))
    (-
     ;; Divisor is always negative. The remainder is positive
     (let ((rem (interval-abs div)))
       (setf (interval-low rem) 0)
       (when (numberp (interval-high rem))
         ;; The remainder never contains the lower bound.
         (setf (interval-high rem) (list (interval-high rem))))
       rem))
    (otherwise
     ;; The divisor can be positive or negative. All bets off.
     ;; The magnitude of remainder is the maximum value of the
     ;; divisor.
     (let ((limit (bound-value (interval-high (interval-abs div)))))
       ;; The bound never reaches the limit, so make the interval open
       (make-interval :low (if limit
                               (list (- limit))
                               limit)
                      :high (list limit))))))

#| Test cases
(ceiling-quotient-bound (make-interval :low 0.3 :high 10.3))
=> #S(INTERVAL :LOW 1 :HIGH 11)
(ceiling-quotient-bound (make-interval :low 0.3 :high '(10.3)))
=> #S(INTERVAL :LOW 1 :HIGH 11)
(ceiling-quotient-bound (make-interval :low 0.3 :high 10))
=> #S(INTERVAL :LOW 1 :HIGH 10)
(ceiling-quotient-bound (make-interval :low 0.3 :high '(10)))
=> #S(INTERVAL :LOW 1 :HIGH 10)
(ceiling-quotient-bound (make-interval :low '(0.3) :high 10.3))
=> #S(INTERVAL :LOW 1 :HIGH 11)
(ceiling-quotient-bound (make-interval :low '(0.0) :high 10.3))
=> #S(INTERVAL :LOW 1 :HIGH 11)
(ceiling-quotient-bound (make-interval :low '(-1.3) :high 10.3))
=> #S(INTERVAL :LOW -1 :HIGH 11)
(ceiling-quotient-bound (make-interval :low '(-1.0) :high 10.3))
=> #S(INTERVAL :LOW 0 :HIGH 11)
(ceiling-quotient-bound (make-interval :low -1.0 :high 10.3))
=> #S(INTERVAL :LOW -1 :HIGH 11)

(ceiling-rem-bound (make-interval :low 0.3 :high 10.3))
=> #S(INTERVAL :LOW (-10.3) :HIGH 0)
(ceiling-rem-bound (make-interval :low 0.3 :high '(10.3)))
=> #S(INTERVAL :LOW 0 :HIGH '(10.3))
(ceiling-rem-bound (make-interval :low -10 :high -2.3))
=> #S(INTERVAL :LOW 0 :HIGH (10))
(ceiling-rem-bound (make-interval :low 0.3 :high 10))
=> #S(INTERVAL :LOW (-10) :HIGH 0)
(ceiling-rem-bound (make-interval :low '(-1.3) :high 10.3))
=> #S(INTERVAL :LOW (-10.3) :HIGH (10.3))
(ceiling-rem-bound (make-interval :low '(-20.3) :high 10.3))
=> #S(INTERVAL :LOW (-20.3) :HIGH (20.3))
|#
\f
(defun truncate-quotient-bound (quot)
  ;; For positive quotients, truncate is exactly like floor. For
  ;; negative quotients, truncate is exactly like ceiling. Otherwise,
  ;; it's the union of the two pieces.
  (case (interval-range-info quot)
    (+
     ;; Just like floor
     (floor-quotient-bound quot))
    (-
     ;; Just like ceiling
     (ceiling-quotient-bound quot))
    (otherwise
     ;; Split the interval into positive and negative pieces, compute
     ;; the result for each piece and put them back together.
     (destructuring-bind (neg pos) (interval-split 0 quot t t)
       (interval-merge-pair (ceiling-quotient-bound neg)
                            (floor-quotient-bound pos))))))

(defun truncate-rem-bound (num div)
  ;; This is significantly more complicated than floor or ceiling. We
  ;; need both the number and the divisor to determine the range. The
  ;; basic idea is to split the ranges of num and den into positive
  ;; and negative pieces and deal with each of the four possibilities
  ;; in turn.
  (case (interval-range-info num)
    (+
     (case (interval-range-info div)
       (+
        (floor-rem-bound div))
       (-
        (ceiling-rem-bound div))
       (otherwise
        (destructuring-bind (neg pos) (interval-split 0 div t t)
          (interval-merge-pair (truncate-rem-bound num neg)
                               (truncate-rem-bound num pos))))))
    (-
     (case (interval-range-info div)
       (+
        (ceiling-rem-bound div))
       (-
        (floor-rem-bound div))
       (otherwise
        (destructuring-bind (neg pos) (interval-split 0 div t t)
          (interval-merge-pair (truncate-rem-bound num neg)
                               (truncate-rem-bound num pos))))))
    (otherwise
     (destructuring-bind (neg pos) (interval-split 0 num t t)
       (interval-merge-pair (truncate-rem-bound neg div)
                            (truncate-rem-bound pos div))))))
)) ; end PROGN's

;;; Derive useful information about the range. Returns three values:
;;; - '+ if its positive, '- negative, or nil if it overlaps 0.
;;; - The abs of the minimal value (i.e. closest to 0) in the range.
;;; - The abs of the maximal value if there is one, or nil if it is
;;;   unbounded.
(defun numeric-range-info (low high)
  (cond ((and low (not (minusp low)))
         (values '+ low high))
        ((and high (not (plusp high)))
         (values '- (- high) (if low (- low) nil)))
        (t
         (values nil 0 (and low high (max (- low) high))))))

(defun integer-truncate-derive-type
       (number-low number-high divisor-low divisor-high)
  ;; The result cannot be larger in magnitude than the number, but the sign
  ;; might change. If we can determine the sign of either the number or
  ;; the divisor, we can eliminate some of the cases.
  (multiple-value-bind (number-sign number-min number-max)
      (numeric-range-info number-low number-high)
    (multiple-value-bind (divisor-sign divisor-min divisor-max)
        (numeric-range-info divisor-low divisor-high)
      (when (and divisor-max (zerop divisor-max))
        ;; We've got a problem: guaranteed division by zero.
        (return-from integer-truncate-derive-type t))
      (when (zerop divisor-min)
        ;; We'll assume that they aren't going to divide by zero.
        (incf divisor-min))
      (cond ((and number-sign divisor-sign)
             ;; We know the sign of both.
             (if (eq number-sign divisor-sign)
                 ;; Same sign, so the result will be positive.
                 `(integer ,(if divisor-max
                                (truncate number-min divisor-max)
                                0)
                           ,(if number-max
                                (truncate number-max divisor-min)
                                '*))
                 ;; Different signs, the result will be negative.
                 `(integer ,(if number-max
                                (- (truncate number-max divisor-min))
                                '*)
                           ,(if divisor-max
                                (- (truncate number-min divisor-max))
                                0))))
            ((eq divisor-sign '+)
             ;; The divisor is positive. Therefore, the number will just
             ;; become closer to zero.
             `(integer ,(if number-low
                            (truncate number-low divisor-min)
                            '*)
                       ,(if number-high
                            (truncate number-high divisor-min)
                            '*)))
            ((eq divisor-sign '-)
             ;; The divisor is negative. Therefore, the absolute value of
             ;; the number will become closer to zero, but the sign will also
             ;; change.
             `(integer ,(if number-high
                            (- (truncate number-high divisor-min))
                            '*)
                       ,(if number-low
                            (- (truncate number-low divisor-min))
                            '*)))
            ;; The divisor could be either positive or negative.
            (number-max
             ;; The number we are dividing has a bound. Divide that by the
             ;; smallest posible divisor.
             (let ((bound (truncate number-max divisor-min)))
               `(integer ,(- bound) ,bound)))
            (t
             ;; The number we are dividing is unbounded, so we can't tell
             ;; anything about the result.
             `integer)))))

#!-propagate-float-type
(defun integer-rem-derive-type
       (number-low number-high divisor-low divisor-high)
  (if (and divisor-low divisor-high)
      ;; We know the range of the divisor, and the remainder must be smaller
      ;; than the divisor. We can tell the sign of the remainer if we know
      ;; the sign of the number.
      (let ((divisor-max (1- (max (abs divisor-low) (abs divisor-high)))))
        `(integer ,(if (or (null number-low)
                           (minusp number-low))
                       (- divisor-max)
                       0)
                  ,(if (or (null number-high)
                           (plusp number-high))
                       divisor-max
                       0)))
      ;; The divisor is potentially either very positive or very negative.
      ;; Therefore, the remainer is unbounded, but we might be able to tell
      ;; something about the sign from the number.
      `(integer ,(if (and number-low (not (minusp number-low)))
                     ;; The number we are dividing is positive. Therefore,
                     ;; the remainder must be positive.
                     0
                     '*)
                ,(if (and number-high (not (plusp number-high)))
                     ;; The number we are dividing is negative. Therefore,
                     ;; the remainder must be negative.
                     0
                     '*))))

#!-propagate-float-type
(defoptimizer (random derive-type) ((bound &optional state))
  (let ((type (continuation-type bound)))
    (when (numeric-type-p type)
      (let ((class (numeric-type-class type))
            (high (numeric-type-high type))
            (format (numeric-type-format type)))
        (make-numeric-type
         :class class
         :format format
         :low (coerce 0 (or format class 'real))
         :high (cond ((not high) nil)
                     ((eq class 'integer) (max (1- high) 0))
                     ((or (consp high) (zerop high)) high)
                     (t `(,high))))))))

#!+propagate-float-type
(defun random-derive-type-aux (type)
  (let ((class (numeric-type-class type))
        (high (numeric-type-high type))
        (format (numeric-type-format type)))
    (make-numeric-type
         :class class
         :format format
         :low (coerce 0 (or format class 'real))
         :high (cond ((not high) nil)
                     ((eq class 'integer) (max (1- high) 0))
                     ((or (consp high) (zerop high)) high)
                     (t `(,high))))))

#!+propagate-float-type
(defoptimizer (random derive-type) ((bound &optional state))
  (one-arg-derive-type bound #'random-derive-type-aux nil))
\f
;;;; logical derive-type methods

;;; Return the maximum number of bits an integer of the supplied type can take
;;; up, or NIL if it is unbounded. The second (third) value is T if the
;;; integer can be positive (negative) and NIL if not. Zero counts as
;;; positive.
(defun integer-type-length (type)
  (if (numeric-type-p type)
      (let ((min (numeric-type-low type))
            (max (numeric-type-high type)))
        (values (and min max (max (integer-length min) (integer-length max)))
                (or (null max) (not (minusp max)))
                (or (null min) (minusp min))))
      (values nil t t)))

#!-propagate-fun-type
(progn
(defoptimizer (logand derive-type) ((x y))
  (multiple-value-bind (x-len x-pos x-neg)
      (integer-type-length (continuation-type x))
    (declare (ignore x-pos))
    (multiple-value-bind (y-len y-pos y-neg)
        (integer-type-length (continuation-type y))
      (declare (ignore y-pos))
      (if (not x-neg)
          ;; X must be positive.
          (if (not y-neg)
              ;; The must both be positive.
              (cond ((or (null x-len) (null y-len))
                     (specifier-type 'unsigned-byte))
                    ((or (zerop x-len) (zerop y-len))
                     (specifier-type '(integer 0 0)))
                    (t
                     (specifier-type `(unsigned-byte ,(min x-len y-len)))))
              ;; X is positive, but Y might be negative.
              (cond ((null x-len)
                     (specifier-type 'unsigned-byte))
                    ((zerop x-len)
                     (specifier-type '(integer 0 0)))
                    (t
                     (specifier-type `(unsigned-byte ,x-len)))))
          ;; X might be negative.
          (if (not y-neg)
              ;; Y must be positive.
              (cond ((null y-len)
                     (specifier-type 'unsigned-byte))
                    ((zerop y-len)
                     (specifier-type '(integer 0 0)))
                    (t
                     (specifier-type
                      `(unsigned-byte ,y-len))))
              ;; Either might be negative.
              (if (and x-len y-len)
                  ;; The result is bounded.
                  (specifier-type `(signed-byte ,(1+ (max x-len y-len))))
                  ;; We can't tell squat about the result.
                  (specifier-type 'integer)))))))

(defoptimizer (logior derive-type) ((x y))
  (multiple-value-bind (x-len x-pos x-neg)
      (integer-type-length (continuation-type x))
    (multiple-value-bind (y-len y-pos y-neg)
        (integer-type-length (continuation-type y))
      (cond
       ((and (not x-neg) (not y-neg))
        ;; Both are positive.
        (specifier-type `(unsigned-byte ,(if (and x-len y-len)
                                             (max x-len y-len)
                                             '*))))
       ((not x-pos)
        ;; X must be negative.
        (if (not y-pos)
            ;; Both are negative. The result is going to be negative and be
            ;; the same length or shorter than the smaller.
            (if (and x-len y-len)
                ;; It's bounded.
                (specifier-type `(integer ,(ash -1 (min x-len y-len)) -1))
                ;; It's unbounded.
                (specifier-type '(integer * -1)))
            ;; X is negative, but we don't know about Y. The result will be
            ;; negative, but no more negative than X.
            (specifier-type
             `(integer ,(or (numeric-type-low (continuation-type x)) '*)
                       -1))))
       (t
        ;; X might be either positive or negative.
        (if (not y-pos)
            ;; But Y is negative. The result will be negative.
            (specifier-type
             `(integer ,(or (numeric-type-low (continuation-type y)) '*)
                       -1))
            ;; We don't know squat about either. It won't get any bigger.
            (if (and x-len y-len)
                ;; Bounded.
                (specifier-type `(signed-byte ,(1+ (max x-len y-len))))
                ;; Unbounded.
                (specifier-type 'integer))))))))

(defoptimizer (logxor derive-type) ((x y))
  (multiple-value-bind (x-len x-pos x-neg)
      (integer-type-length (continuation-type x))
    (multiple-value-bind (y-len y-pos y-neg)
        (integer-type-length (continuation-type y))
      (cond
       ((or (and (not x-neg) (not y-neg))
            (and (not x-pos) (not y-pos)))
        ;; Either both are negative or both are positive. The result will be
        ;; positive, and as long as the longer.
        (specifier-type `(unsigned-byte ,(if (and x-len y-len)
                                             (max x-len y-len)
                                             '*))))
       ((or (and (not x-pos) (not y-neg))
            (and (not y-neg) (not y-pos)))
        ;; Either X is negative and Y is positive of vice-verca. The result
        ;; will be negative.
        (specifier-type `(integer ,(if (and x-len y-len)
                                       (ash -1 (max x-len y-len))
                                       '*)
                                  -1)))
       ;; We can't tell what the sign of the result is going to be. All we
       ;; know is that we don't create new bits.
       ((and x-len y-len)
        (specifier-type `(signed-byte ,(1+ (max x-len y-len)))))
       (t
        (specifier-type 'integer))))))

) ; PROGN

#!+propagate-fun-type
(progn
(defun logand-derive-type-aux (x y &optional same-leaf)
  (declare (ignore same-leaf))
  (multiple-value-bind (x-len x-pos x-neg) (integer-type-length x)
    (declare (ignore x-pos))
    (multiple-value-bind (y-len y-pos y-neg) (integer-type-length  y)
      (declare (ignore y-pos))
      (if (not x-neg)
          ;; X must be positive.
          (if (not y-neg)
              ;; The must both be positive.
              (cond ((or (null x-len) (null y-len))
                     (specifier-type 'unsigned-byte))
                    ((or (zerop x-len) (zerop y-len))
                     (specifier-type '(integer 0 0)))
                    (t
                     (specifier-type `(unsigned-byte ,(min x-len y-len)))))
              ;; X is positive, but Y might be negative.
              (cond ((null x-len)
                     (specifier-type 'unsigned-byte))
                    ((zerop x-len)
                     (specifier-type '(integer 0 0)))
                    (t
                     (specifier-type `(unsigned-byte ,x-len)))))
          ;; X might be negative.
          (if (not y-neg)
              ;; Y must be positive.
              (cond ((null y-len)
                     (specifier-type 'unsigned-byte))
                    ((zerop y-len)
                     (specifier-type '(integer 0 0)))
                    (t
                     (specifier-type
                      `(unsigned-byte ,y-len))))
              ;; Either might be negative.
              (if (and x-len y-len)
                  ;; The result is bounded.
                  (specifier-type `(signed-byte ,(1+ (max x-len y-len))))
                  ;; We can't tell squat about the result.
                  (specifier-type 'integer)))))))

(defun logior-derive-type-aux (x y &optional same-leaf)
  (declare (ignore same-leaf))
  (multiple-value-bind (x-len x-pos x-neg) (integer-type-length x)
    (multiple-value-bind (y-len y-pos y-neg) (integer-type-length y)
      (cond
       ((and (not x-neg) (not y-neg))
        ;; Both are positive.
        (if (and x-len y-len (zerop x-len) (zerop y-len))
            (specifier-type '(integer 0 0))
            (specifier-type `(unsigned-byte ,(if (and x-len y-len)
                                             (max x-len y-len)
                                             '*)))))
       ((not x-pos)
        ;; X must be negative.
        (if (not y-pos)
            ;; Both are negative. The result is going to be negative and be
            ;; the same length or shorter than the smaller.
            (if (and x-len y-len)
                ;; It's bounded.
                (specifier-type `(integer ,(ash -1 (min x-len y-len)) -1))
                ;; It's unbounded.
                (specifier-type '(integer * -1)))
            ;; X is negative, but we don't know about Y. The result will be
            ;; negative, but no more negative than X.
            (specifier-type
             `(integer ,(or (numeric-type-low x) '*)
                       -1))))
       (t
        ;; X might be either positive or negative.
        (if (not y-pos)
            ;; But Y is negative. The result will be negative.
            (specifier-type
             `(integer ,(or (numeric-type-low y) '*)
                       -1))
            ;; We don't know squat about either. It won't get any bigger.
            (if (and x-len y-len)
                ;; Bounded.
                (specifier-type `(signed-byte ,(1+ (max x-len y-len))))
                ;; Unbounded.
                (specifier-type 'integer))))))))

(defun logxor-derive-type-aux (x y &optional same-leaf)
  (declare (ignore same-leaf))
  (multiple-value-bind (x-len x-pos x-neg) (integer-type-length x)
    (multiple-value-bind (y-len y-pos y-neg) (integer-type-length y)
      (cond
       ((or (and (not x-neg) (not y-neg))
            (and (not x-pos) (not y-pos)))
        ;; Either both are negative or both are positive. The result will be
        ;; positive, and as long as the longer.
        (if (and x-len y-len (zerop x-len) (zerop y-len))
            (specifier-type '(integer 0 0))
            (specifier-type `(unsigned-byte ,(if (and x-len y-len)
                                             (max x-len y-len)
                                             '*)))))
       ((or (and (not x-pos) (not y-neg))
            (and (not y-neg) (not y-pos)))
        ;; Either X is negative and Y is positive of vice-verca. The result
        ;; will be negative.
        (specifier-type `(integer ,(if (and x-len y-len)
                                       (ash -1 (max x-len y-len))
                                       '*)
                                  -1)))
       ;; We can't tell what the sign of the result is going to be. All we
       ;; know is that we don't create new bits.
       ((and x-len y-len)
        (specifier-type `(signed-byte ,(1+ (max x-len y-len)))))
       (t
        (specifier-type 'integer))))))

(macrolet ((frob (logfcn)
             (let ((fcn-aux (symbolicate logfcn "-DERIVE-TYPE-AUX")))
             `(defoptimizer (,logfcn derive-type) ((x y))
                (two-arg-derive-type x y #',fcn-aux #',logfcn)))))
  ;; FIXME: DEF-FROB, not just FROB
  (frob logand)
  (frob logior)
  (frob logxor))

(defoptimizer (integer-length derive-type) ((x))
  (let ((x-type (continuation-type x)))
    (when (and (numeric-type-p x-type)
               (csubtypep x-type (specifier-type 'integer)))
      ;; If the X is of type (INTEGER LO HI), then the integer-length
      ;; of X is (INTEGER (min lo hi) (max lo hi), basically.  Be
      ;; careful about LO or HI being NIL, though.  Also, if 0 is
      ;; contained in X, the lower bound is obviously 0.
      (flet ((null-or-min (a b)
               (and a b (min (integer-length a)
                             (integer-length b))))
             (null-or-max (a b)
               (and a b (max (integer-length a)
                             (integer-length b)))))
        (let* ((min (numeric-type-low x-type))
               (max (numeric-type-high x-type))
               (min-len (null-or-min min max))
               (max-len (null-or-max min max)))
          (when (ctypep 0 x-type)
            (setf min-len 0))
          (specifier-type `(integer ,(or min-len '*) ,(or max-len '*))))))))
) ; PROGN
\f
;;;; miscellaneous derive-type methods

(defoptimizer (code-char derive-type) ((code))
  (specifier-type 'base-char))

(defoptimizer (values derive-type) ((&rest values))
  (values-specifier-type
   `(values ,@(mapcar #'(lambda (x)
                          (type-specifier (continuation-type x)))
                      values))))
\f
;;;; byte operations
;;;;
;;;; We try to turn byte operations into simple logical operations. First, we
;;;; convert byte specifiers into separate size and position arguments passed
;;;; to internal %FOO functions. We then attempt to transform the %FOO
;;;; functions into boolean operations when the size and position are constant
;;;; and the operands are fixnums.

(macrolet (;; Evaluate body with SIZE-VAR and POS-VAR bound to expressions that
           ;; evaluate to the SIZE and POSITION of the byte-specifier form
           ;; SPEC. We may wrap a let around the result of the body to bind
           ;; some variables.
           ;;
           ;; If the spec is a BYTE form, then bind the vars to the subforms.
           ;; otherwise, evaluate SPEC and use the BYTE-SIZE and BYTE-POSITION.
           ;; The goal of this transformation is to avoid consing up byte
           ;; specifiers and then immediately throwing them away.
           (with-byte-specifier ((size-var pos-var spec) &body body)
             (once-only ((spec `(macroexpand ,spec))
                         (temp '(gensym)))
                        `(if (and (consp ,spec)
                                  (eq (car ,spec) 'byte)
                                  (= (length ,spec) 3))
                        (let ((,size-var (second ,spec))
                              (,pos-var (third ,spec)))
                          ,@body)
                        (let ((,size-var `(byte-size ,,temp))
                              (,pos-var `(byte-position ,,temp)))
                          `(let ((,,temp ,,spec))
                             ,,@body))))))

  (def-source-transform ldb (spec int)
    (with-byte-specifier (size pos spec)
      `(%ldb ,size ,pos ,int)))

  (def-source-transform dpb (newbyte spec int)
    (with-byte-specifier (size pos spec)
      `(%dpb ,newbyte ,size ,pos ,int)))

  (def-source-transform mask-field (spec int)
    (with-byte-specifier (size pos spec)
      `(%mask-field ,size ,pos ,int)))

  (def-source-transform deposit-field (newbyte spec int)
    (with-byte-specifier (size pos spec)
      `(%deposit-field ,newbyte ,size ,pos ,int))))

(defoptimizer (%ldb derive-type) ((size posn num))
  (let ((size (continuation-type size)))
    (if (and (numeric-type-p size)
             (csubtypep size (specifier-type 'integer)))
        (let ((size-high (numeric-type-high size)))
          (if (and size-high (<= size-high sb!vm:word-bits))
              (specifier-type `(unsigned-byte ,size-high))
              (specifier-type 'unsigned-byte)))
        *universal-type*)))

(defoptimizer (%mask-field derive-type) ((size posn num))
  (let ((size (continuation-type size))
        (posn (continuation-type posn)))
    (if (and (numeric-type-p size)
             (csubtypep size (specifier-type 'integer))
             (numeric-type-p posn)
             (csubtypep posn (specifier-type 'integer)))
        (let ((size-high (numeric-type-high size))
              (posn-high (numeric-type-high posn)))
          (if (and size-high posn-high
                   (<= (+ size-high posn-high) sb!vm:word-bits))
              (specifier-type `(unsigned-byte ,(+ size-high posn-high)))
              (specifier-type 'unsigned-byte)))
        *universal-type*)))

(defoptimizer (%dpb derive-type) ((newbyte size posn int))
  (let ((size (continuation-type size))
        (posn (continuation-type posn))
        (int (continuation-type int)))
    (if (and (numeric-type-p size)
             (csubtypep size (specifier-type 'integer))
             (numeric-type-p posn)
             (csubtypep posn (specifier-type 'integer))
             (numeric-type-p int)
             (csubtypep int (specifier-type 'integer)))
        (let ((size-high (numeric-type-high size))
              (posn-high (numeric-type-high posn))
              (high (numeric-type-high int))
              (low (numeric-type-low int)))
          (if (and size-high posn-high high low
                   (<= (+ size-high posn-high) sb!vm:word-bits))
              (specifier-type
               (list (if (minusp low) 'signed-byte 'unsigned-byte)
                     (max (integer-length high)
                          (integer-length low)
                          (+ size-high posn-high))))
              *universal-type*))
        *universal-type*)))

(defoptimizer (%deposit-field derive-type) ((newbyte size posn int))
  (let ((size (continuation-type size))
        (posn (continuation-type posn))
        (int (continuation-type int)))
    (if (and (numeric-type-p size)
             (csubtypep size (specifier-type 'integer))
             (numeric-type-p posn)
             (csubtypep posn (specifier-type 'integer))
             (numeric-type-p int)
             (csubtypep int (specifier-type 'integer)))
        (let ((size-high (numeric-type-high size))
              (posn-high (numeric-type-high posn))
              (high (numeric-type-high int))
              (low (numeric-type-low int)))
          (if (and size-high posn-high high low
                   (<= (+ size-high posn-high) sb!vm:word-bits))
              (specifier-type
               (list (if (minusp low) 'signed-byte 'unsigned-byte)
                     (max (integer-length high)
                          (integer-length low)
                          (+ size-high posn-high))))
              *universal-type*))
        *universal-type*)))

(deftransform %ldb ((size posn int)
                    (fixnum fixnum integer)
                    (unsigned-byte #.sb!vm:word-bits))
  "convert to inline logical operations"
  `(logand (ash int (- posn))
           (ash ,(1- (ash 1 sb!vm:word-bits))
                (- size ,sb!vm:word-bits))))

(deftransform %mask-field ((size posn int)
                           (fixnum fixnum integer)
                           (unsigned-byte #.sb!vm:word-bits))
  "convert to inline logical operations"
  `(logand int
           (ash (ash ,(1- (ash 1 sb!vm:word-bits))
                     (- size ,sb!vm:word-bits))
                posn)))

;;; Note: for %DPB and %DEPOSIT-FIELD, we can't use
;;;   (OR (SIGNED-BYTE N) (UNSIGNED-BYTE N))
;;; as the result type, as that would allow result types
;;; that cover the range -2^(n-1) .. 1-2^n, instead of allowing result types
;;; of (UNSIGNED-BYTE N) and result types of (SIGNED-BYTE N).

(deftransform %dpb ((new size posn int)
                    *
                    (unsigned-byte #.sb!vm:word-bits))
  "convert to inline logical operations"
  `(let ((mask (ldb (byte size 0) -1)))
     (logior (ash (logand new mask) posn)
             (logand int (lognot (ash mask posn))))))

(deftransform %dpb ((new size posn int)
                    *
                    (signed-byte #.sb!vm:word-bits))
  "convert to inline logical operations"
  `(let ((mask (ldb (byte size 0) -1)))
     (logior (ash (logand new mask) posn)
             (logand int (lognot (ash mask posn))))))

(deftransform %deposit-field ((new size posn int)
                              *
                              (unsigned-byte #.sb!vm:word-bits))
  "convert to inline logical operations"
  `(let ((mask (ash (ldb (byte size 0) -1) posn)))
     (logior (logand new mask)
             (logand int (lognot mask)))))

(deftransform %deposit-field ((new size posn int)
                              *
                              (signed-byte #.sb!vm:word-bits))
  "convert to inline logical operations"
  `(let ((mask (ash (ldb (byte size 0) -1) posn)))
     (logior (logand new mask)
             (logand int (lognot mask)))))
\f
;;; miscellanous numeric transforms

;;; If a constant appears as the first arg, swap the args.
(deftransform commutative-arg-swap ((x y) * * :defun-only t :node node)
  (if (and (constant-continuation-p x)
           (not (constant-continuation-p y)))
      `(,(continuation-function-name (basic-combination-fun node))
        y
        ,(continuation-value x))
      (give-up-ir1-transform)))

(dolist (x '(= char= + * logior logand logxor))
  (%deftransform x '(function * *) #'commutative-arg-swap
                 "place constant arg last."))

;;; Handle the case of a constant BOOLE-CODE.
(deftransform boole ((op x y) * * :when :both)
  "convert to inline logical operations"
  (unless (constant-continuation-p op)
    (give-up-ir1-transform "BOOLE code is not a constant."))
  (let ((control (continuation-value op)))
    (case control
      (#.boole-clr 0)
      (#.boole-set -1)
      (#.boole-1 'x)
      (#.boole-2 'y)
      (#.boole-c1 '(lognot x))
      (#.boole-c2 '(lognot y))
      (#.boole-and '(logand x y))
      (#.boole-ior '(logior x y))
      (#.boole-xor '(logxor x y))
      (#.boole-eqv '(logeqv x y))
      (#.boole-nand '(lognand x y))
      (#.boole-nor '(lognor x y))
      (#.boole-andc1 '(logandc1 x y))
      (#.boole-andc2 '(logandc2 x y))
      (#.boole-orc1 '(logorc1 x y))
      (#.boole-orc2 '(logorc2 x y))
      (t
       (abort-ir1-transform "~S is an illegal control arg to BOOLE."
                            control)))))
\f
;;;; converting special case multiply/divide to shifts

;;; If arg is a constant power of two, turn * into a shift.
(deftransform * ((x y) (integer integer) * :when :both)
  "convert x*2^k to shift"
  (unless (constant-continuation-p y)
    (give-up-ir1-transform))
  (let* ((y (continuation-value y))
         (y-abs (abs y))
         (len (1- (integer-length y-abs))))
    (unless (= y-abs (ash 1 len))
      (give-up-ir1-transform))
    (if (minusp y)
        `(- (ash x ,len))
        `(ash x ,len))))

;;; If both arguments and the result are (unsigned-byte 32), try to come up
;;; with a ``better'' multiplication using multiplier recoding. There are two
;;; different ways the multiplier can be recoded. The more obvious is to shift
;;; X by the correct amount for each bit set in Y and to sum the results. But
;;; if there is a string of bits that are all set, you can add X shifted by
;;; one more then the bit position of the first set bit and subtract X shifted
;;; by the bit position of the last set bit. We can't use this second method
;;; when the high order bit is bit 31 because shifting by 32 doesn't work
;;; too well.
(deftransform * ((x y)
                 ((unsigned-byte 32) (unsigned-byte 32))
                 (unsigned-byte 32))
  "recode as shift and add"
  (unless (constant-continuation-p y)
    (give-up-ir1-transform))
  (let ((y (continuation-value y))
        (result nil)
        (first-one nil))
    (labels ((tub32 (x) `(truly-the (unsigned-byte 32) ,x))
             (add (next-factor)
               (setf result
                     (tub32
                      (if result
                          `(+ ,result ,(tub32 next-factor))
                          next-factor)))))
      (declare (inline add))
      (dotimes (bitpos 32)
        (if first-one
            (when (not (logbitp bitpos y))
              (add (if (= (1+ first-one) bitpos)
                       ;; There is only a single bit in the string.
                       `(ash x ,first-one)
                       ;; There are at least two.
                       `(- ,(tub32 `(ash x ,bitpos))
                           ,(tub32 `(ash x ,first-one)))))
              (setf first-one nil))
            (when (logbitp bitpos y)
              (setf first-one bitpos))))
      (when first-one
        (cond ((= first-one 31))
              ((= first-one 30)
               (add '(ash x 30)))
              (t
               (add `(- ,(tub32 '(ash x 31)) ,(tub32 `(ash x ,first-one))))))
        (add '(ash x 31))))
    (or result 0)))

;;; If arg is a constant power of two, turn FLOOR into a shift and mask.
;;; If CEILING, add in (1- (ABS Y)) and then do FLOOR.
(flet ((frob (y ceil-p)
         (unless (constant-continuation-p y)
           (give-up-ir1-transform))
         (let* ((y (continuation-value y))
                (y-abs (abs y))
                (len (1- (integer-length y-abs))))
           (unless (= y-abs (ash 1 len))
             (give-up-ir1-transform))
           (let ((shift (- len))
                 (mask (1- y-abs)))
             `(let ,(when ceil-p `((x (+ x ,(1- y-abs)))))
                ,(if (minusp y)
                     `(values (ash (- x) ,shift)
                              (- (logand (- x) ,mask)))
                     `(values (ash x ,shift)
                              (logand x ,mask))))))))
  (deftransform floor ((x y) (integer integer) *)
    "convert division by 2^k to shift"
    (frob y nil))
  (deftransform ceiling ((x y) (integer integer) *)
    "convert division by 2^k to shift"
    (frob y t)))

;;; Do the same for MOD.
(deftransform mod ((x y) (integer integer) * :when :both)
  "convert remainder mod 2^k to LOGAND"
  (unless (constant-continuation-p y)
    (give-up-ir1-transform))
  (let* ((y (continuation-value y))
         (y-abs (abs y))
         (len (1- (integer-length y-abs))))
    (unless (= y-abs (ash 1 len))
      (give-up-ir1-transform))
    (let ((mask (1- y-abs)))
      (if (minusp y)
          `(- (logand (- x) ,mask))
          `(logand x ,mask)))))

;;; If arg is a constant power of two, turn TRUNCATE into a shift and mask.
(deftransform truncate ((x y) (integer integer))
  "convert division by 2^k to shift"
  (unless (constant-continuation-p y)
    (give-up-ir1-transform))
  (let* ((y (continuation-value y))
         (y-abs (abs y))
         (len (1- (integer-length y-abs))))
    (unless (= y-abs (ash 1 len))
      (give-up-ir1-transform))
    (let* ((shift (- len))
           (mask (1- y-abs)))
      `(if (minusp x)
           (values ,(if (minusp y)
                        `(ash (- x) ,shift)
                        `(- (ash (- x) ,shift)))
                   (- (logand (- x) ,mask)))
           (values ,(if (minusp y)
                        `(- (ash (- x) ,shift))
                        `(ash x ,shift))
                   (logand x ,mask))))))

;;; And the same for REM.
(deftransform rem ((x y) (integer integer) * :when :both)
  "convert remainder mod 2^k to LOGAND"
  (unless (constant-continuation-p y)
    (give-up-ir1-transform))
  (let* ((y (continuation-value y))
         (y-abs (abs y))
         (len (1- (integer-length y-abs))))
    (unless (= y-abs (ash 1 len))
      (give-up-ir1-transform))
    (let ((mask (1- y-abs)))
      `(if (minusp x)
           (- (logand (- x) ,mask))
           (logand x ,mask)))))
\f
;;;; arithmetic and logical identity operation elimination
;;;;
;;;; Flush calls to various arith functions that convert to the identity
;;;; function or a constant.

(dolist (stuff '((ash 0 x)
                 (logand -1 x)
                 (logand 0 0)
                 (logior 0 x)
                 (logior -1 -1)
                 (logxor -1 (lognot x))
                 (logxor 0 x)))
  (destructuring-bind (name identity result) stuff
    (deftransform name ((x y) `(* (constant-argument (member ,identity))) '*
                        :eval-name t :when :both)
      "fold identity operations"
      result)))

;;; These are restricted to rationals, because (- 0 0.0) is 0.0, not -0.0, and
;;; (* 0 -4.0) is -0.0.
(deftransform - ((x y) ((constant-argument (member 0)) rational) *
                 :when :both)
  "convert (- 0 x) to negate"
  '(%negate y))
(deftransform * ((x y) (rational (constant-argument (member 0))) *
                 :when :both)
  "convert (* x 0) to 0."
  0)

;;; Return T if in an arithmetic op including continuations X and Y, the
;;; result type is not affected by the type of X. That is, Y is at least as
;;; contagious as X.
#+nil
(defun not-more-contagious (x y)
  (declare (type continuation x y))
  (let ((x (continuation-type x))
        (y (continuation-type y)))
    (values (type= (numeric-contagion x y)
                   (numeric-contagion y y)))))
;;; Patched version by Raymond Toy. dtc: Should be safer although it
;;; needs more work as valid transforms are missed; some cases are
;;; specific to particular transform functions so the use of this
;;; function may need a re-think.
(defun not-more-contagious (x y)
  (declare (type continuation x y))
  (flet ((simple-numeric-type (num)
           (and (numeric-type-p num)
                ;; Return non-NIL if NUM is integer, rational, or a float
                ;; of some type (but not FLOAT)
                (case (numeric-type-class num)
                  ((integer rational)
                   t)
                  (float
                   (numeric-type-format num))
                  (t
                   nil)))))
    (let ((x (continuation-type x))
          (y (continuation-type y)))
      (if (and (simple-numeric-type x)
               (simple-numeric-type y))
          (values (type= (numeric-contagion x y)
                         (numeric-contagion y y)))))))

;;; Fold (+ x 0).
;;;
;;;    If y is not constant, not zerop, or is contagious, or a
;;; positive float +0.0 then give up.
(deftransform + ((x y) (t (constant-argument t)) * :when :both)
  "fold zero arg"
  (let ((val (continuation-value y)))
    (unless (and (zerop val)
                 (not (and (floatp val) (plusp (float-sign val))))
                 (not-more-contagious y x))
      (give-up-ir1-transform)))
  'x)

;;; Fold (- x 0).
;;;
;;;    If y is not constant, not zerop, or is contagious, or a
;;; negative float -0.0 then give up.
(deftransform - ((x y) (t (constant-argument t)) * :when :both)
  "fold zero arg"
  (let ((val (continuation-value y)))
    (unless (and (zerop val)
                 (not (and (floatp val) (minusp (float-sign val))))
                 (not-more-contagious y x))
      (give-up-ir1-transform)))
  'x)

;;; Fold (OP x +/-1)
(dolist (stuff '((* x (%negate x))
                 (/ x (%negate x))
                 (expt x (/ 1 x))))
  (destructuring-bind (name result minus-result) stuff
    (deftransform name ((x y) '(t (constant-argument real)) '* :eval-name t
                        :when :both)
      "fold identity operations"
      (let ((val (continuation-value y)))
        (unless (and (= (abs val) 1)
                     (not-more-contagious y x))
          (give-up-ir1-transform))
        (if (minusp val) minus-result result)))))

;;; Fold (expt x n) into multiplications for small integral values of
;;; N; convert (expt x 1/2) to sqrt.
(deftransform expt ((x y) (t (constant-argument real)) *)
  "recode as multiplication or sqrt"
  (let ((val (continuation-value y)))
    ;; If Y would cause the result to be promoted to the same type as
    ;; Y, we give up. If not, then the result will be the same type
    ;; as X, so we can replace the exponentiation with simple
    ;; multiplication and division for small integral powers.
    (unless (not-more-contagious y x)
      (give-up-ir1-transform))
    (cond ((zerop val) '(float 1 x))
          ((= val 2) '(* x x))
          ((= val -2) '(/ (* x x)))
          ((= val 3) '(* x x x))
          ((= val -3) '(/ (* x x x)))
          ((= val 1/2) '(sqrt x))
          ((= val -1/2) '(/ (sqrt x)))
          (t (give-up-ir1-transform)))))

;;; KLUDGE: Shouldn't (/ 0.0 0.0), etc. cause exceptions in these
;;; transformations?
;;; Perhaps we should have to prove that the denominator is nonzero before
;;; doing them? (Also the DOLIST over macro calls is weird. Perhaps
;;; just FROB?) -- WHN 19990917
;;;
;;; FIXME: What gives with the single quotes in the argument lists
;;; for DEFTRANSFORMs here? Does that work? Is it needed? Why?
(dolist (name '(ash /))
  (deftransform name ((x y) '((constant-argument (integer 0 0)) integer) '*
                      :eval-name t :when :both)
    "fold zero arg"
    0))
(dolist (name '(truncate round floor ceiling))
  (deftransform name ((x y) '((constant-argument (integer 0 0)) integer) '*
                      :eval-name t :when :both)
    "fold zero arg"
    '(values 0 0)))
\f
;;;; character operations

(deftransform char-equal ((a b) (base-char base-char))
  "open code"
  '(let* ((ac (char-code a))
          (bc (char-code b))
          (sum (logxor ac bc)))
     (or (zerop sum)
         (when (eql sum #x20)
           (let ((sum (+ ac bc)))
             (and (> sum 161) (< sum 213)))))))

(deftransform char-upcase ((x) (base-char))
  "open code"
  '(let ((n-code (char-code x)))
     (if (and (> n-code #o140)  ; Octal 141 is #\a.
              (< n-code #o173)) ; Octal 172 is #\z.
         (code-char (logxor #x20 n-code))
         x)))

(deftransform char-downcase ((x) (base-char))
  "open code"
  '(let ((n-code (char-code x)))
     (if (and (> n-code 64)     ; 65 is #\A.
              (< n-code 91))    ; 90 is #\Z.
         (code-char (logxor #x20 n-code))
         x)))
\f
;;;; equality predicate transforms

;;; Return true if X and Y are continuations whose only use is a reference
;;; to the same leaf, and the value of the leaf cannot change.
(defun same-leaf-ref-p (x y)
  (declare (type continuation x y))
  (let ((x-use (continuation-use x))
        (y-use (continuation-use y)))
    (and (ref-p x-use)
         (ref-p y-use)
         (eq (ref-leaf x-use) (ref-leaf y-use))
         (constant-reference-p x-use))))

;;; If X and Y are the same leaf, then the result is true. Otherwise, if
;;; there is no intersection between the types of the arguments, then the
;;; result is definitely false.
(deftransform simple-equality-transform ((x y) * *
                                         :defun-only t
                                         :when :both)
  (cond ((same-leaf-ref-p x y)
         't)
        ((not (types-intersect (continuation-type x) (continuation-type y)))
         'nil)
        (t
         (give-up-ir1-transform))))

(dolist (x '(eq char= equal))
  (%deftransform x '(function * *) #'simple-equality-transform))

;;; Similar to SIMPLE-EQUALITY-PREDICATE, except that we also try to
;;; convert to a type-specific predicate or EQ:
;;; -- If both args are characters, convert to CHAR=. This is better than
;;;    just converting to EQ, since CHAR= may have special compilation
;;;    strategies for non-standard representations, etc.
;;; -- If either arg is definitely not a number, then we can compare
;;;    with EQ.
;;; -- Otherwise, we try to put the arg we know more about second. If X
;;;    is constant then we put it second. If X is a subtype of Y, we put
;;;    it second. These rules make it easier for the back end to match
;;;    these interesting cases.
;;; -- If Y is a fixnum, then we quietly pass because the back end can
;;;    handle that case, otherwise give an efficency note.
(deftransform eql ((x y) * * :when :both)
  "convert to simpler equality predicate"
  (let ((x-type (continuation-type x))
        (y-type (continuation-type y))
        (char-type (specifier-type 'character))
        (number-type (specifier-type 'number)))
    (cond ((same-leaf-ref-p x y)
           't)
          ((not (types-intersect x-type y-type))
           'nil)
          ((and (csubtypep x-type char-type)
                (csubtypep y-type char-type))
           '(char= x y))
          ((or (not (types-intersect x-type number-type))
               (not (types-intersect y-type number-type)))
           '(eq x y))
          ((and (not (constant-continuation-p y))
                (or (constant-continuation-p x)
                    (and (csubtypep x-type y-type)
                         (not (csubtypep y-type x-type)))))
           '(eql y x))
          (t
           (give-up-ir1-transform)))))

;;; Convert to EQL if both args are rational and complexp is specified
;;; and the same for both.
(deftransform = ((x y) * * :when :both)
  "open code"
  (let ((x-type (continuation-type x))
        (y-type (continuation-type y)))
    (if (and (csubtypep x-type (specifier-type 'number))
             (csubtypep y-type (specifier-type 'number)))
        (cond ((or (and (csubtypep x-type (specifier-type 'float))
                        (csubtypep y-type (specifier-type 'float)))
                   (and (csubtypep x-type (specifier-type '(complex float)))
                        (csubtypep y-type (specifier-type '(complex float)))))
               ;; They are both floats. Leave as = so that -0.0 is
               ;; handled correctly.
               (give-up-ir1-transform))
              ((or (and (csubtypep x-type (specifier-type 'rational))
                        (csubtypep y-type (specifier-type 'rational)))
                   (and (csubtypep x-type (specifier-type '(complex rational)))
                        (csubtypep y-type (specifier-type '(complex rational)))))
               ;; They are both rationals and complexp is the same. Convert
               ;; to EQL.
               '(eql x y))
              (t
               (give-up-ir1-transform
                "The operands might not be the same type.")))
        (give-up-ir1-transform
         "The operands might not be the same type."))))

;;; If Cont's type is a numeric type, then return the type, otherwise
;;; GIVE-UP-IR1-TRANSFORM.
(defun numeric-type-or-lose (cont)
  (declare (type continuation cont))
  (let ((res (continuation-type cont)))
    (unless (numeric-type-p res) (give-up-ir1-transform))
    res))

;;; See whether we can statically determine (< X Y) using type information.
;;; If X's high bound is < Y's low, then X < Y. Similarly, if X's low is >=
;;; to Y's high, the X >= Y (so return NIL). If not, at least make sure any
;;; constant arg is second.
;;;
;;; KLUDGE: Why should constant argument be second? It would be nice to find
;;; out and explain. -- WHN 19990917
#!-propagate-float-type
(defun ir1-transform-< (x y first second inverse)
  (if (same-leaf-ref-p x y)
      'nil
      (let* ((x-type (numeric-type-or-lose x))
             (x-lo (numeric-type-low x-type))
             (x-hi (numeric-type-high x-type))
             (y-type (numeric-type-or-lose y))
             (y-lo (numeric-type-low y-type))
             (y-hi (numeric-type-high y-type)))
        (cond ((and x-hi y-lo (< x-hi y-lo))
               't)
              ((and y-hi x-lo (>= x-lo y-hi))
               'nil)
              ((and (constant-continuation-p first)
                    (not (constant-continuation-p second)))
               `(,inverse y x))
              (t
               (give-up-ir1-transform))))))
#!+propagate-float-type
(defun ir1-transform-< (x y first second inverse)
  (if (same-leaf-ref-p x y)
      'nil
      (let ((xi (numeric-type->interval (numeric-type-or-lose x)))
            (yi (numeric-type->interval (numeric-type-or-lose y))))
        (cond ((interval-< xi yi)
               't)
              ((interval->= xi yi)
               'nil)
              ((and (constant-continuation-p first)
                    (not (constant-continuation-p second)))
               `(,inverse y x))
              (t
               (give-up-ir1-transform))))))

(deftransform < ((x y) (integer integer) * :when :both)
  (ir1-transform-< x y x y '>))

(deftransform > ((x y) (integer integer) * :when :both)
  (ir1-transform-< y x x y '<))

#!+propagate-float-type
(deftransform < ((x y) (float float) * :when :both)
  (ir1-transform-< x y x y '>))

#!+propagate-float-type
(deftransform > ((x y) (float float) * :when :both)
  (ir1-transform-< y x x y '<))
\f
;;;; converting N-arg comparisons
;;;;
;;;; We convert calls to N-arg comparison functions such as < into
;;;; two-arg calls. This transformation is enabled for all such
;;;; comparisons in this file. If any of these predicates are not
;;;; open-coded, then the transformation should be removed at some
;;;; point to avoid pessimization.

;;; This function is used for source transformation of N-arg
;;; comparison functions other than inequality. We deal both with
;;; converting to two-arg calls and inverting the sense of the test,
;;; if necessary. If the call has two args, then we pass or return a
;;; negated test as appropriate. If it is a degenerate one-arg call,
;;; then we transform to code that returns true. Otherwise, we bind
;;; all the arguments and expand into a bunch of IFs.
(declaim (ftype (function (symbol list boolean) *) multi-compare))
(defun multi-compare (predicate args not-p)
  (let ((nargs (length args)))
    (cond ((< nargs 1) (values nil t))
          ((= nargs 1) `(progn ,@args t))
          ((= nargs 2)
           (if not-p
               `(if (,predicate ,(first args) ,(second args)) nil t)
               (values nil t)))
          (t
           (do* ((i (1- nargs) (1- i))
                 (last nil current)
                 (current (gensym) (gensym))
                 (vars (list current) (cons current vars))
                 (result 't (if not-p
                                `(if (,predicate ,current ,last)
                                     nil ,result)
                                `(if (,predicate ,current ,last)
                                     ,result nil))))
               ((zerop i)
                `((lambda ,vars ,result) . ,args)))))))

(def-source-transform = (&rest args) (multi-compare '= args nil))
(def-source-transform < (&rest args) (multi-compare '< args nil))
(def-source-transform > (&rest args) (multi-compare '> args nil))
(def-source-transform <= (&rest args) (multi-compare '> args t))
(def-source-transform >= (&rest args) (multi-compare '< args t))

(def-source-transform char= (&rest args) (multi-compare 'char= args nil))
(def-source-transform char< (&rest args) (multi-compare 'char< args nil))
(def-source-transform char> (&rest args) (multi-compare 'char> args nil))
(def-source-transform char<= (&rest args) (multi-compare 'char> args t))
(def-source-transform char>= (&rest args) (multi-compare 'char< args t))

(def-source-transform char-equal (&rest args) (multi-compare 'char-equal args nil))
(def-source-transform char-lessp (&rest args) (multi-compare 'char-lessp args nil))
(def-source-transform char-greaterp (&rest args)
  (multi-compare 'char-greaterp args nil))
(def-source-transform char-not-greaterp (&rest args)
  (multi-compare 'char-greaterp args t))
(def-source-transform char-not-lessp (&rest args) (multi-compare 'char-lessp args t))

;;; This function does source transformation of N-arg inequality
;;; functions such as /=. This is similar to Multi-Compare in the <3
;;; arg cases. If there are more than two args, then we expand into
;;; the appropriate n^2 comparisons only when speed is important.
(declaim (ftype (function (symbol list) *) multi-not-equal))
(defun multi-not-equal (predicate args)
  (let ((nargs (length args)))
    (cond ((< nargs 1) (values nil t))
          ((= nargs 1) `(progn ,@args t))
          ((= nargs 2)
           `(if (,predicate ,(first args) ,(second args)) nil t))
          ((not (policy nil (and (>= speed space)
                                 (>= speed compilation-speed))))
           (values nil t))
          (t
           (let ((vars (make-gensym-list nargs)))
             (do ((var vars next)
                  (next (cdr vars) (cdr next))
                  (result 't))
                 ((null next)
                  `((lambda ,vars ,result) . ,args))
               (let ((v1 (first var)))
                 (dolist (v2 next)
                   (setq result `(if (,predicate ,v1 ,v2) nil ,result))))))))))

(def-source-transform /= (&rest args) (multi-not-equal '= args))
(def-source-transform char/= (&rest args) (multi-not-equal 'char= args))
(def-source-transform char-not-equal (&rest args) (multi-not-equal 'char-equal args))

;;; Expand MAX and MIN into the obvious comparisons.
(def-source-transform max (arg &rest more-args)
  (if (null more-args)
      `(values ,arg)
      (once-only ((arg1 arg)
                  (arg2 `(max ,@more-args)))
        `(if (> ,arg1 ,arg2)
             ,arg1 ,arg2))))
(def-source-transform min (arg &rest more-args)
  (if (null more-args)
      `(values ,arg)
      (once-only ((arg1 arg)
                  (arg2 `(min ,@more-args)))
        `(if (< ,arg1 ,arg2)
             ,arg1 ,arg2))))
\f
;;;; converting N-arg arithmetic functions
;;;;
;;;; N-arg arithmetic and logic functions are associated into two-arg
;;;; versions, and degenerate cases are flushed.

;;; Left-associate First-Arg and More-Args using Function.
(declaim (ftype (function (symbol t list) list) associate-arguments))
(defun associate-arguments (function first-arg more-args)
  (let ((next (rest more-args))
        (arg (first more-args)))
    (if (null next)
        `(,function ,first-arg ,arg)
        (associate-arguments function `(,function ,first-arg ,arg) next))))

;;; Do source transformations for transitive functions such as +.
;;; One-arg cases are replaced with the arg and zero arg cases with
;;; the identity. If LEAF-FUN is true, then replace two-arg calls with
;;; a call to that function.
(defun source-transform-transitive (fun args identity &optional leaf-fun)
  (declare (symbol fun leaf-fun) (list args))
  (case (length args)
    (0 identity)
    (1 `(values ,(first args)))
    (2 (if leaf-fun
           `(,leaf-fun ,(first args) ,(second args))
           (values nil t)))
    (t
     (associate-arguments fun (first args) (rest args)))))

(def-source-transform + (&rest args) (source-transform-transitive '+ args 0))
(def-source-transform * (&rest args) (source-transform-transitive '* args 1))
(def-source-transform logior (&rest args)
  (source-transform-transitive 'logior args 0))
(def-source-transform logxor (&rest args)
  (source-transform-transitive 'logxor args 0))
(def-source-transform logand (&rest args)
  (source-transform-transitive 'logand args -1))

(def-source-transform logeqv (&rest args)
  (if (evenp (length args))
      `(lognot (logxor ,@args))
      `(logxor ,@args)))

;;; Note: we can't use SOURCE-TRANSFORM-TRANSITIVE for GCD and LCM
;;; because when they are given one argument, they return its absolute
;;; value.

(def-source-transform gcd (&rest args)
  (case (length args)
    (0 0)
    (1 `(abs (the integer ,(first args))))
    (2 (values nil t))
    (t (associate-arguments 'gcd (first args) (rest args)))))

(def-source-transform lcm (&rest args)
  (case (length args)
    (0 1)
    (1 `(abs (the integer ,(first args))))
    (2 (values nil t))
    (t (associate-arguments 'lcm (first args) (rest args)))))

;;; Do source transformations for intransitive n-arg functions such as
;;; /. With one arg, we form the inverse. With two args we pass.
;;; Otherwise we associate into two-arg calls.
(declaim (ftype (function (symbol list t) list) source-transform-intransitive))
(defun source-transform-intransitive (function args inverse)
  (case (length args)
    ((0 2) (values nil t))
    (1 `(,@inverse ,(first args)))
    (t (associate-arguments function (first args) (rest args)))))

(def-source-transform - (&rest args)
  (source-transform-intransitive '- args '(%negate)))
(def-source-transform / (&rest args)
  (source-transform-intransitive '/ args '(/ 1)))
\f
;;;; transforming APPLY

;;; We convert APPLY into MULTIPLE-VALUE-CALL so that the compiler
;;; only needs to understand one kind of variable-argument call. It is
;;; more efficient to convert APPLY to MV-CALL than MV-CALL to APPLY.
(def-source-transform apply (fun arg &rest more-args)
  (let ((args (cons arg more-args)))
    `(multiple-value-call ,fun
       ,@(mapcar #'(lambda (x)
                     `(values ,x))
                 (butlast args))
       (values-list ,(car (last args))))))
\f
;;;; transforming FORMAT
;;;;
;;;; If the control string is a compile-time constant, then replace it
;;;; with a use of the FORMATTER macro so that the control string is
;;;; ``compiled.'' Furthermore, if the destination is either a stream
;;;; or T and the control string is a function (i.e. FORMATTER), then
;;;; convert the call to FORMAT to just a FUNCALL of that function.

(deftransform format ((dest control &rest args) (t simple-string &rest t) *
                      :policy (> speed space))
  (unless (constant-continuation-p control)
    (give-up-ir1-transform "The control string is not a constant."))
  (let ((arg-names (make-gensym-list (length args))))
    `(lambda (dest control ,@arg-names)
       (declare (ignore control))
       (format dest (formatter ,(continuation-value control)) ,@arg-names))))

(deftransform format ((stream control &rest args) (stream function &rest t) *
                      :policy (> speed space))
  (let ((arg-names (make-gensym-list (length args))))
    `(lambda (stream control ,@arg-names)
       (funcall control stream ,@arg-names)
       nil)))

(deftransform format ((tee control &rest args) ((member t) function &rest t) *
                      :policy (> speed space))
  (let ((arg-names (make-gensym-list (length args))))
    `(lambda (tee control ,@arg-names)
       (declare (ignore tee))
       (funcall control *standard-output* ,@arg-names)
       nil)))