(let ((predicate-function (%coerce-callable-to-fun predicate))
(key-function (and key (%coerce-callable-to-fun key))))
(typecase sequence
- (list (sort-list sequence predicate-function key-function))
+ (list (stable-sort-list sequence predicate-function key-function))
(vector
(with-array-data ((vector (the vector sequence))
(start 0)
(defun stable-sort (sequence predicate &key key)
#!+sb-doc
- "Destructively sorts sequence. Predicate should return non-Nil if
- Arg1 is to precede Arg2."
+ "Destructively sort SEQUENCE. PREDICATE should return non-NIL if
+ ARG1 is to precede ARG2."
(typecase sequence
(simple-vector
(stable-sort-simple-vector sequence predicate key))
(list
- (sort-list sequence predicate key))
+ (stable-sort-list sequence predicate key))
(vector
(stable-sort-vector sequence predicate key))
(t
:expected-type 'sequence
:format-control "~S is not a sequence."
:format-arguments (list sequence)))))
+\f
+;;; APPLY-KEYED-PRED saves us a function call sometimes.
+(eval-when (:compile-toplevel :execute)
+ (sb!xc:defmacro apply-keyed-pred (one two pred key)
+ `(if ,key
+ (funcall ,pred (funcall ,key ,one)
+ (funcall ,key ,two))
+ (funcall ,pred ,one ,two)))
+) ; EVAL-WHEN
+\f
+;;;; stable sort of lists
-;;; stable sort of lists
+(defun last-cons-of (list)
+ (loop (let ((rest (rest list)))
+ (if rest
+ (setf list rest)
+ (return list)))))
-;;; SORT-LIST uses a bottom up merge sort. First a pass is made over
-;;; the list grabbing one element at a time and merging it with the
-;;; next one form pairs of sorted elements. Then n is doubled, and
-;;; elements are taken in runs of two, merging one run with the next
-;;; to form quadruples of sorted elements. This continues until n is
-;;; large enough that the inner loop only runs for one iteration; that
-;;; is, there are only two runs that can be merged, the first run
+;;; Destructively merge LIST-1 with LIST-2 (given that they're already
+;;; sorted w.r.t. PRED-FUN on KEY-FUN, giving output sorted the same
+;;; way). In the resulting list, elements of LIST-1 are guaranteed to
+;;; come before equal elements of LIST-2.
+;;;
+;;; Return (VALUES HEAD TAILTAIL), where HEAD is the same value you'd
+;;; expect from MERGE, and TAILTAIL is the last cons in the list (i.e.
+;;; the last cons in the list which NRECONC calls TAIL).
+(defun merge-lists* (list-1 list-2 pred-fun key-fun)
+ (declare (type list list-1 list-2))
+ (declare (type function pred-fun key-fun))
+ (cond ((null list-1) (values list-2 (last-cons-of list-2)))
+ ((null list-2) (values list-1 (last-cons-of list-1)))
+ (t (let* ((reversed-result-so-far nil)
+ (key-1 (funcall key-fun (car list-1)))
+ (key-2 (funcall key-fun (car list-2))))
+ (loop
+ (macrolet ((frob (list-i key-i other-list)
+ `(progn
+ ;; basically
+ ;; (PUSH (POP ,LIST-I) REVERSED-RESULT-SO-FAR),
+ ;; except doing some fancy footwork to
+ ;; reuse the cons cell:
+ (psetf (cdr ,list-i) reversed-result-so-far
+ reversed-result-so-far ,list-i
+ ,list-i (cdr ,list-i))
+ ;; Now maybe we're done.
+ (if (endp ,list-i)
+ (return (values (nreconc
+ reversed-result-so-far
+ ,other-list)
+ (last-cons-of
+ ,other-list)))
+ (setf ,key-i
+ (funcall key-fun (car ,list-i)))))))
+ ;; Note that by making KEY-2 the first arg to
+ ;; PRED-FUN, we arrange that if PRED-FUN is a function
+ ;; in the #'< style, the outcome is stably sorted.
+ (if (funcall pred-fun key-2 key-1)
+ (frob list-2 key-2 list-1)
+ (frob list-1 key-1 list-2))))))))
+
+;;; STABLE-SORT-LIST uses a bottom-up merge sort. First a pass is made
+;;; over the list grabbing one element at a time and merging it with
+;;; the next one to form pairs of sorted elements. Then N is doubled,
+;;; and elements are taken in runs of two, merging one run with the
+;;; next to form quadruples of sorted elements. This continues until N
+;;; is large enough that the inner loop only runs for one iteration;
+;;; that is, there are only two runs that can be merged, the first run
;;; starting at the beginning of the list, and the second being the
;;; remaining elements.
-
-(defun sort-list (list pred key)
+(defun stable-sort-list (list pred key)
(let ((head (cons :header list)) ; head holds on to everything
(n 1) ; bottom-up size of lists to be merged
unsorted ; unsorted is the remaining list to be
; broken into n size lists and merged
list-1 ; list-1 is one length n list to be merged
- last) ; last points to the last visited cell
+ last ; last points to the last visited cell
+ (pred-fun (%coerce-callable-to-fun pred))
+ (key-fun (if key
+ (%coerce-callable-to-fun key)
+ #'identity)))
(declare (fixnum n))
(loop
- ;; start collecting runs of n at the first element
+ ;; Start collecting runs of N at the first element.
(setf unsorted (cdr head))
- ;; tack on the first merge of two n-runs to the head holder
+ ;; Tack on the first merge of two N-runs to the head holder.
(setf last head)
(let ((n-1 (1- n)))
(declare (fixnum n-1))
(let ((temp (nthcdr n-1 list-1))
list-2)
(cond (temp
- ;; there are enough elements for a second run
+ ;; There are enough elements for a second run.
(setf list-2 (cdr temp))
(setf (cdr temp) nil)
(setf temp (nthcdr n-1 list-2))
(cond (temp
(setf unsorted (cdr temp))
(setf (cdr temp) nil))
- ;; the second run goes off the end of the list
+ ;; The second run goes off the end of the list.
(t (setf unsorted nil)))
(multiple-value-bind (merged-head merged-last)
- (merge-lists* list-1 list-2 pred key)
- (setf (cdr last) merged-head)
- (setf last merged-last))
+ (merge-lists* list-1 list-2 pred-fun key-fun)
+ (setf (cdr last) merged-head
+ last merged-last))
(if (null unsorted) (return)))
- ;; if there is only one run, then tack it on to the end
+ ;; If there is only one run, then tack it on to the end.
(t (setf (cdr last) list-1)
(return)))))
(setf n (ash n 1)) ; (+ n n)
;; iteration to realize.
(if (eq list-1 (cdr head))
(return list-1))))))
-
-;;; APPLY-PRED saves us a function call sometimes.
-(eval-when (:compile-toplevel :execute)
- (sb!xc:defmacro apply-pred (one two pred key)
- `(if ,key
- (funcall ,pred (funcall ,key ,one)
- (funcall ,key ,two))
- (funcall ,pred ,one ,two)))
-) ; EVAL-WHEN
-
-(defvar *merge-lists-header* (list :header))
-
-;;; MERGE-LISTS* originally written by Jim Large.
-;;; modified to return a pointer to the end of the result
-;;; and to not cons header each time its called.
-;;; It destructively merges list-1 with list-2. In the resulting
-;;; list, elements of list-2 are guaranteed to come after equal elements
-;;; of list-1.
-(defun merge-lists* (list-1 list-2 pred key)
- (let* ((result *merge-lists-header*)
- (merge-lists-trailer (cdr *merge-lists-header*)))
- (unwind-protect
- (do ((P result)) ; points to last cell of result
- ((or (null list-1) (null list-2)) ; done when either list used up
- (if (null list-1) ; in which case, append the
- (rplacd p list-2) ; other list
- (rplacd p list-1))
- (do ((drag p lead)
- (lead (cdr p) (cdr lead)))
- ((null lead)
- (values (cdr result) ; Return the result sans header
- drag)))) ; and return pointer to last element.
- (cond ((apply-pred (car list-2) (car list-1) pred key)
- (rplacd p list-2) ; Append the lesser list to last cell of
- (setq p (cdr p)) ; result. Note: test must be done for
- (pop list-2)) ; LIST-2 < LIST-1 so merge will be
- (T (rplacd p list-1) ; stable for LIST-1.
- (setq p (cdr p))
- (pop list-1))))
- (setf (cdr result) merge-lists-trailer) ; (free memory, be careful)
- )))
-
-;;; stable sort of vectors
+\f
+;;;; stable sort of vectors
;;; Stable sorting vectors is done with the same algorithm used for
;;; lists, using a temporary vector to merge back and forth between it
(incf ,target-i)
(incf ,i))
(return))
- ((apply-pred (,source-ref ,source ,j)
- (,source-ref ,source ,i)
- ,pred ,key)
+ ((apply-keyed-pred (,source-ref ,source ,j)
+ (,source-ref ,source ,i)
+ ,pred ,key)
(setf (,target-ref ,target ,target-i)
(,source-ref ,source ,j))
(incf ,j))
(defun stable-sort-vector (vector pred key)
(vector-merge-sort vector pred key aref))
-
+\f
;;;; merging
(eval-when (:compile-toplevel :execute)
(incf ,result-i)
(incf ,i))
(return ,result-vector))
- ((apply-pred (,access ,vector-2 ,j) (,access ,vector-1 ,i)
- ,pred ,key)
+ ((apply-keyed-pred (,access ,vector-2 ,j) (,access ,vector-1 ,i)
+ ,pred ,key)
(setf (,access ,result-vector ,result-i)
(,access ,vector-2 ,j))
(incf ,j))
#!+sb-doc
"Merge the sequences SEQUENCE1 and SEQUENCE2 destructively into a
sequence of type RESULT-TYPE using PREDICATE to order the elements."
+ ;; FIXME: This implementation is remarkably inefficient in various
+ ;; ways. In decreasing order of estimated user astonishment, I note:
+ ;; full calls to SPECIFIER-TYPE at runtime; copying input vectors
+ ;; to lists before doing MERGE-LISTS*; and walking input lists
+ ;; (because of the call to MERGE-LISTS*, which walks the list to
+ ;; find the last element for its second return value) even in cases
+ ;; like (MERGE 'LIST (LIST 1) (LIST 2 3 4 5 ... 1000)) where one list
+ ;; can be largely ignored. -- WHN 2003-01-05
(let ((type (specifier-type result-type)))
(cond
((csubtypep type (specifier-type 'list))
;; reimplementing everything, we can't do the same for the LIST
;; case, so do relevant length checking here:
(let ((s1 (coerce sequence1 'list))
- (s2 (coerce sequence2 'list)))
+ (s2 (coerce sequence2 'list))
+ (pred-fun (%coerce-callable-to-fun predicate))
+ (key-fun (if key
+ (%coerce-callable-to-fun key)
+ #'identity)))
(when (type= type (specifier-type 'list))
- (return-from merge (values (merge-lists* s1 s2 predicate key))))
+ (return-from merge (values (merge-lists* s1 s2 pred-fun key-fun))))
(when (eq type *empty-type*)
(bad-sequence-type-error nil))
(when (type= type (specifier-type 'null))
(if (csubtypep (specifier-type '(cons nil t)) type)
(if (and (null s1) (null s2))
(sequence-type-length-mismatch-error type 0)
- (values (merge-lists* s1 s2 predicate key)))
+ (values (merge-lists* s1 s2 pred-fun key-fun)))
(sequence-type-too-hairy result-type))))
((csubtypep type (specifier-type 'vector))
(let* ((vector-1 (coerce sequence1 'vector))
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