X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcode%2Fbignum.lisp;h=054e6dfd17b56e6b77c5d4f31ea528c528358896;hb=0f3a5f2e8886d18d0b4f6485c38a42be629422ae;hp=03f23377ab672d40899065e3c00ab4d75fc8a280;hpb=6cc71ab8ffad49f43895ad0a1df6885c81876687;p=sbcl.git

diff --git a/src/code/bignum.lisp b/src/code/bignum.lisp
index 03f2337..054e6df 100644
--- a/src/code/bignum.lisp
+++ b/src/code/bignum.lisp
@@ -20,7 +20,7 @@
 ;;;       bignum-ashift-right bignum-ashift-left bignum-gcd
 ;;;       bignum-to-float bignum-integer-length
 ;;;       bignum-logical-and bignum-logical-ior bignum-logical-xor
-;;;       bignum-logical-not bignum-load-byte bignum-deposit-byte
+;;;       bignum-logical-not bignum-load-byte
 ;;;       bignum-truncate bignum-plus-p bignum-compare make-small-bignum
 ;;;       bignum-logbitp bignum-logcount
 ;;;   These symbols define the interface to the compiler:
@@ -28,7 +28,7 @@
 ;;;       %bignum-length %bignum-set-length %bignum-ref %bignum-set
 ;;;       %digit-0-or-plusp %add-with-carry %subtract-with-borrow
 ;;;       %multiply-and-add %multiply %lognot %logand %logior %logxor
-;;;       %fixnum-to-digit %floor %fixnum-digit-with-correct-sign %ashl
+;;;       %fixnum-to-digit %bigfloor %fixnum-digit-with-correct-sign %ashl
 ;;;       %ashr %digit-logical-shift-right))
 
 ;;; The following interfaces will either be assembler routines or code
@@ -41,7 +41,7 @@
 ;;;       %BIGNUM-SET-LENGTH
 ;;;       %FIXNUM-DIGIT-WITH-CORRECT-SIGN
 ;;;       %SIGN-DIGIT
-;;;	  %ASHR
+;;;       %ASHR
 ;;;       %ASHL
 ;;;       %BIGNUM-0-OR-PLUSP
 ;;;       %DIGIT-LOGICAL-SHIFT-RIGHT
@@ -67,13 +67,13 @@
 ;;;    LDB
 ;;;       %FIXNUM-TO-DIGIT
 ;;;    TRUNCATE
-;;;       %FLOOR
+;;;       %BIGFLOOR
 ;;;
 ;;; Note: The floating routines know about the float representation.
 ;;;
 ;;; PROBLEM 1:
 ;;; There might be a problem with various LET's and parameters that take a
-;;; digit value. We need to write these so those things stay in 32-bit
+;;; digit value. We need to write these so those things stay in machine
 ;;; registers and number stack slots. I bind locals to these values, and I
 ;;; use function on them -- ZEROP, ASH, etc.
 ;;;
@@ -87,12 +87,12 @@
 ;;;    fixnums
 ;;;       logior, logxor, logand
 ;;;       depending on relationals, < (twice) and <= (twice)
-;;;	  or write compare thing (twice).
+;;;       or write compare thing (twice).
 ;;;       LDB on fixnum with bignum result.
 ;;;       DPB on fixnum with bignum result.
 ;;;       TRUNCATE returns zero or one as one value and fixnum or minus fixnum
-;;;	  for the other value when given (truncate fixnum bignum).
-;;;	  Returns (truncate bignum fixnum) otherwise.
+;;;       for the other value when given (truncate fixnum bignum).
+;;;       Returns (truncate bignum fixnum) otherwise.
 ;;;       addition
 ;;;       subtraction (twice)
 ;;;       multiply
@@ -100,17 +100,20 @@
 ;;;    Write MASK-FIELD and DEPOSIT-FIELD in terms of logical operations.
 ;;;    DIVIDE
 ;;;       IF (/ x y) with bignums:
-;;;	  do the truncate, and if rem is 0, return quotient.
-;;;	  if rem is non-0
-;;;	     gcd of x and y.
-;;;	     "truncate" each by gcd, ignoring remainder 0.
-;;;	     form ratio of each result, bottom is positive.
+;;;       do the truncate, and if rem is 0, return quotient.
+;;;       if rem is non-0
+;;;          gcd of x and y.
+;;;          "truncate" each by gcd, ignoring remainder 0.
+;;;          form ratio of each result, bottom is positive.
 
 ;;;; What's a bignum?
 
-(defconstant digit-size 32)
+(defconstant digit-size sb!vm:n-word-bits)
 
-(defconstant maximum-bignum-length (1- (ash 1 (- 32 sb!vm:n-widetag-bits))))
+(defconstant maximum-bignum-length (1- (ash 1 (- sb!vm:n-word-bits
+                                                 sb!vm:n-widetag-bits))))
+
+(defconstant all-ones-digit (1- (ash 1 sb!vm:n-word-bits)))
 
 ;;;; internal inline routines
 
@@ -125,15 +128,15 @@
   (%bignum-length bignum))
 
 ;;; %BIGNUM-REF needs to access bignums as obviously as possible, and it needs
-;;; to be able to return 32 bits somewhere no one looks for real objects.
+;;; to be able to return the digit somewhere no one looks for real objects.
 (defun %bignum-ref (bignum i)
   (declare (type bignum-type bignum)
-	   (type bignum-index i))
+           (type bignum-index i))
   (%bignum-ref bignum i))
 (defun %bignum-set (bignum i value)
   (declare (type bignum-type bignum)
-	   (type bignum-index i)
-	   (type bignum-element-type value))
+           (type bignum-index i)
+           (type bignum-element-type value))
   (%bignum-set bignum i value))
 
 ;;; Return T if digit is positive, or NIL if negative.
@@ -144,44 +147,45 @@
 #!-sb-fluid (declaim (inline %bignum-0-or-plusp))
 (defun %bignum-0-or-plusp (bignum len)
   (declare (type bignum-type bignum)
-	   (type bignum-index len))
+           (type bignum-index len))
   (%digit-0-or-plusp (%bignum-ref bignum (1- len))))
 
-;;; This should be in assembler, and should not cons intermediate results. It
-;;; returns a 32bit digit and a carry resulting from adding together a, b, and
-;;; an incoming carry.
+;;; This should be in assembler, and should not cons intermediate
+;;; results. It returns a bignum digit and a carry resulting from adding
+;;; together a, b, and an incoming carry.
 (defun %add-with-carry (a b carry)
   (declare (type bignum-element-type a b)
-	   (type (mod 2) carry))
+           (type (mod 2) carry))
   (%add-with-carry a b carry))
 
-;;; This should be in assembler, and should not cons intermediate results. It
-;;; returns a 32bit digit and a borrow resulting from subtracting b from a, and
-;;; subtracting a possible incoming borrow.
+;;; This should be in assembler, and should not cons intermediate
+;;; results. It returns a bignum digit and a borrow resulting from
+;;; subtracting b from a, and subtracting a possible incoming borrow.
 ;;;
 ;;; We really do:  a - b - 1 + borrow, where borrow is either 0 or 1.
 (defun %subtract-with-borrow (a b borrow)
   (declare (type bignum-element-type a b)
-	   (type (mod 2) borrow))
+           (type (mod 2) borrow))
   (%subtract-with-borrow a b borrow))
 
-;;; Multiply two digit-size (32-bit) numbers, returning a 64-bit result
-;;; split into two 32-bit quantities.
+;;; Multiply two digit-size numbers, returning a 2*digit-size result
+;;; split into two digit-size quantities.
 (defun %multiply (x y)
   (declare (type bignum-element-type x y))
   (%multiply x y))
 
 ;;; This multiplies x-digit and y-digit, producing high and low digits
 ;;; manifesting the result. Then it adds the low digit, res-digit, and
-;;; carry-in-digit. Any carries (note, you still have to add two digits at a
-;;; time possibly producing two carries) from adding these three digits get
-;;; added to the high digit from the multiply, producing the next carry digit.
-;;; Res-digit is optional since two uses of this primitive multiplies a single
-;;; digit bignum by a multiple digit bignum, and in this situation there is no
-;;; need for a result buffer accumulating partial results which is where the
-;;; res-digit comes from.
+;;; carry-in-digit. Any carries (note, you still have to add two digits
+;;; at a time possibly producing two carries) from adding these three
+;;; digits get added to the high digit from the multiply, producing the
+;;; next carry digit.  Res-digit is optional since two uses of this
+;;; primitive multiplies a single digit bignum by a multiple digit
+;;; bignum, and in this situation there is no need for a result buffer
+;;; accumulating partial results which is where the res-digit comes
+;;; from.
 (defun %multiply-and-add (x-digit y-digit carry-in-digit
-			  &optional (res-digit 0))
+                          &optional (res-digit 0))
   (declare (type bignum-element-type x-digit y-digit res-digit carry-in-digit))
   (%multiply-and-add x-digit y-digit carry-in-digit res-digit))
 
@@ -189,8 +193,8 @@
   (declare (type bignum-element-type digit))
   (%lognot digit))
 
-;;; Each of these does the 32-bit unsigned op.
-#!-sb-fluid (declaim (inline %logand %logior %logxor))
+;;; Each of these does the digit-size unsigned op.
+(declaim (inline %logand %logior %logxor))
 (defun %logand (a b)
   (declare (type bignum-element-type a b))
   (logand a b))
@@ -201,24 +205,24 @@
   (declare (type bignum-element-type a b))
   (logxor a b))
 
-;;; This takes a fixnum and sets it up as an unsigned 32-bit quantity. In
-;;; the new system this will mean shifting it right two bits.
+;;; This takes a fixnum and sets it up as an unsigned digit-size
+;;; quantity.
 (defun %fixnum-to-digit (x)
   (declare (fixnum x))
   (logand x (1- (ash 1 digit-size))))
 
 #!-32x16-divide
 ;;; This takes three digits and returns the FLOOR'ed result of
-;;; dividing the first two as a 64-bit integer by the third.
+;;; dividing the first two as a 2*digit-size integer by the third.
 ;;;
 ;;; Do weird LET and SETQ stuff to bamboozle the compiler into allowing
-;;; the %FLOOR transform to expand into pseudo-assembler for which the
+;;; the %BIGFLOOR transform to expand into pseudo-assembler for which the
 ;;; compiler can later correctly allocate registers.
-(defun %floor (a b c)
+(defun %bigfloor (a b c)
   (let ((a a) (b b) (c c))
     (declare (type bignum-element-type a b c))
     (setq a a b b c c)
-    (%floor a b c)))
+    (%bigfloor a b c)))
 
 ;;; Convert the digit to a regular integer assuming that the digit is signed.
 (defun %fixnum-digit-with-correct-sign (digit)
@@ -231,27 +235,27 @@
 ;;; unsigned.
 (defun %ashr (data count)
   (declare (type bignum-element-type data)
-	   (type (mod 32) count))
+           (type (mod #.sb!vm:n-word-bits) count))
   (%ashr data count))
 
-;;; This takes a 32-bit quantity and shifts it to the left, returning a 32-bit
-;;; quantity.
+;;; This takes a digit-size quantity and shifts it to the left,
+;;; returning a digit-size quantity.
 (defun %ashl (data count)
   (declare (type bignum-element-type data)
-	   (type (mod 32) count))
+           (type (mod #.sb!vm:n-word-bits) count))
   (%ashl data count))
 
 ;;; Do an unsigned (logical) right shift of a digit by Count.
 (defun %digit-logical-shift-right (data count)
   (declare (type bignum-element-type data)
-	   (type (mod 32) count))
+           (type (mod #.sb!vm:n-word-bits) count))
   (%digit-logical-shift-right data count))
 
 ;;; Change the length of bignum to be newlen. Newlen must be the same or
 ;;; smaller than the old length, and any elements beyond newlen must be zeroed.
 (defun %bignum-set-length (bignum newlen)
   (declare (type bignum-type bignum)
-	   (type bignum-index newlen))
+           (type bignum-index newlen))
   (%bignum-set-length bignum newlen))
 
 ;;; This returns 0 or "-1" depending on whether the bignum is positive. This
@@ -261,12 +265,12 @@
 #!-sb-fluid (declaim (inline %sign-digit))
 (defun %sign-digit (bignum len)
   (declare (type bignum-type bignum)
-	   (type bignum-index len))
+           (type bignum-index len))
   (%ashr (%bignum-ref bignum (1- len)) (1- digit-size)))
 
-;;; These take two 32 bit quantities and compare or contrast them without
-;;; wasting time with incorrect type checking.
-#!-sb-fluid (declaim (inline %digit-compare %digit-greater))
+;;; These take two digit-size quantities and compare or contrast them
+;;; without wasting time with incorrect type checking.
+(declaim (inline %digit-compare %digit-greater))
 (defun %digit-compare (x y)
   (= x y))
 (defun %digit-greater (x y)
@@ -279,50 +283,50 @@
 (defun add-bignums (a b)
   (declare (type bignum-type a b))
   (let ((len-a (%bignum-length a))
-	(len-b (%bignum-length b)))
+        (len-b (%bignum-length b)))
     (declare (type bignum-index len-a len-b))
     (multiple-value-bind (a len-a b len-b)
-	(if (> len-a len-b)
-	    (values a len-a b len-b)
-	    (values b len-b a len-a))
+        (if (> len-a len-b)
+            (values a len-a b len-b)
+            (values b len-b a len-a))
       (declare (type bignum-type a b)
-	       (type bignum-index len-a len-b))
+               (type bignum-index len-a len-b))
       (let* ((len-res (1+ len-a))
-	     (res (%allocate-bignum len-res))
-	     (carry 0))
-	(declare (type bignum-index len-res)
-		 (type bignum-type res)
-		 (type (mod 2) carry))
-	(dotimes (i len-b)
-	  (declare (type bignum-index i))
-	  (multiple-value-bind (v k)
-	      (%add-with-carry (%bignum-ref a i) (%bignum-ref b i) carry)
-	    (declare (type bignum-element-type v)
-		     (type (mod 2) k))
-	    (setf (%bignum-ref res i) v)
-	    (setf carry k)))
-	(if (/= len-a len-b)
-	    (finish-add a res carry (%sign-digit b len-b) len-b len-a)
-	    (setf (%bignum-ref res len-a)
-		  (%add-with-carry (%sign-digit a len-a)
-				   (%sign-digit b len-b)
-				   carry)))
-	(%normalize-bignum res len-res)))))
+             (res (%allocate-bignum len-res))
+             (carry 0))
+        (declare (type bignum-index len-res)
+                 (type bignum-type res)
+                 (type (mod 2) carry))
+        (dotimes (i len-b)
+          (declare (type bignum-index i))
+          (multiple-value-bind (v k)
+              (%add-with-carry (%bignum-ref a i) (%bignum-ref b i) carry)
+            (declare (type bignum-element-type v)
+                     (type (mod 2) k))
+            (setf (%bignum-ref res i) v)
+            (setf carry k)))
+        (if (/= len-a len-b)
+            (finish-add a res carry (%sign-digit b len-b) len-b len-a)
+            (setf (%bignum-ref res len-a)
+                  (%add-with-carry (%sign-digit a len-a)
+                                   (%sign-digit b len-b)
+                                   carry)))
+        (%normalize-bignum res len-res)))))
 
 ;;; This takes the longer of two bignums and propagates the carry through its
 ;;; remaining high order digits.
 (defun finish-add (a res carry sign-digit-b start end)
   (declare (type bignum-type a res)
-	   (type (mod 2) carry)
-	   (type bignum-element-type sign-digit-b)
-	   (type bignum-index start end))
+           (type (mod 2) carry)
+           (type bignum-element-type sign-digit-b)
+           (type bignum-index start end))
   (do ((i start (1+ i)))
       ((= i end)
        (setf (%bignum-ref res end)
-	     (%add-with-carry (%sign-digit a end) sign-digit-b carry)))
+             (%add-with-carry (%sign-digit a end) sign-digit-b carry)))
     (declare (type bignum-index i))
     (multiple-value-bind (v k)
-	(%add-with-carry (%bignum-ref a i) sign-digit-b carry)
+        (%add-with-carry (%bignum-ref a i) sign-digit-b carry)
       (setf (%bignum-ref res i) v)
       (setf carry k)))
   (values))
@@ -335,27 +339,20 @@
 ;;; function to call that fixes up the result returning any useful values, such
 ;;; as the result. This macro may evaluate its arguments more than once.
 (sb!xc:defmacro subtract-bignum-loop (a len-a b len-b res len-res return-fun)
-  (let ((borrow (gensym))
-	(a-digit (gensym))
-	(a-sign (gensym))
-	(b-digit (gensym))
-	(b-sign (gensym))
-	(i (gensym))
-	(v (gensym))
-	(k (gensym)))
+  (with-unique-names (borrow a-digit a-sign b-digit b-sign i v k)
     `(let* ((,borrow 1)
-	    (,a-sign (%sign-digit ,a ,len-a))
-	    (,b-sign (%sign-digit ,b ,len-b)))
+            (,a-sign (%sign-digit ,a ,len-a))
+            (,b-sign (%sign-digit ,b ,len-b)))
        (declare (type bignum-element-type ,a-sign ,b-sign))
        (dotimes (,i ,len-res)
-	 (declare (type bignum-index ,i))
-	 (let ((,a-digit (if (< ,i ,len-a) (%bignum-ref ,a ,i) ,a-sign))
-	       (,b-digit (if (< ,i ,len-b) (%bignum-ref ,b ,i) ,b-sign)))
-	   (declare (type bignum-element-type ,a-digit ,b-digit))
-	   (multiple-value-bind (,v ,k)
-	       (%subtract-with-borrow ,a-digit ,b-digit ,borrow)
-	     (setf (%bignum-ref ,res ,i) ,v)
-	     (setf ,borrow ,k))))
+         (declare (type bignum-index ,i))
+         (let ((,a-digit (if (< ,i ,len-a) (%bignum-ref ,a ,i) ,a-sign))
+               (,b-digit (if (< ,i ,len-b) (%bignum-ref ,b ,i) ,b-sign)))
+           (declare (type bignum-element-type ,a-digit ,b-digit))
+           (multiple-value-bind (,v ,k)
+               (%subtract-with-borrow ,a-digit ,b-digit ,borrow)
+             (setf (%bignum-ref ,res ,i) ,v)
+             (setf ,borrow ,k))))
        (,return-fun ,res ,len-res))))
 
 ) ;EVAL-WHEN
@@ -363,76 +360,81 @@
 (defun subtract-bignum (a b)
   (declare (type bignum-type a b))
   (let* ((len-a (%bignum-length a))
-	 (len-b (%bignum-length b))
-	 (len-res (1+ (max len-a len-b)))
-	 (res (%allocate-bignum len-res)))
+         (len-b (%bignum-length b))
+         (len-res (1+ (max len-a len-b)))
+         (res (%allocate-bignum len-res)))
     (declare (type bignum-index len-a len-b len-res)) ;Test len-res for bounds?
     (subtract-bignum-loop a len-a b len-b res len-res %normalize-bignum)))
 
 ;;; Operations requiring a subtraction without the overhead of intermediate
 ;;; results, such as GCD, use this. It assumes Result is big enough for the
 ;;; result.
+(defun subtract-bignum-buffers-with-len (a len-a b len-b result len-res)
+  (declare (type bignum-type a b result)
+           (type bignum-index len-a len-b len-res))
+  (subtract-bignum-loop a len-a b len-b result len-res
+                        %normalize-bignum-buffer))
+
 (defun subtract-bignum-buffers (a len-a b len-b result)
-  (declare (type bignum-type a b)
-	   (type bignum-index len-a len-b))
-  (let ((len-res (max len-a len-b)))
-    (subtract-bignum-loop a len-a b len-b result len-res
-			  %normalize-bignum-buffer)))
+  (declare (type bignum-type a b result)
+           (type bignum-index len-a len-b))
+  (subtract-bignum-loop a len-a b len-b result (max len-a len-b)
+                        %normalize-bignum-buffer))
 
 ;;;; multiplication
 
 (defun multiply-bignums (a b)
   (declare (type bignum-type a b))
   (let* ((a-plusp (%bignum-0-or-plusp a (%bignum-length a)))
-	 (b-plusp (%bignum-0-or-plusp b (%bignum-length b)))
-	 (a (if a-plusp a (negate-bignum a)))
-	 (b (if b-plusp b (negate-bignum b)))
-	 (len-a (%bignum-length a))
-	 (len-b (%bignum-length b))
-	 (len-res (+ len-a len-b))
-	 (res (%allocate-bignum len-res))
-	 (negate-res (not (eq a-plusp b-plusp))))
+         (b-plusp (%bignum-0-or-plusp b (%bignum-length b)))
+         (a (if a-plusp a (negate-bignum a)))
+         (b (if b-plusp b (negate-bignum b)))
+         (len-a (%bignum-length a))
+         (len-b (%bignum-length b))
+         (len-res (+ len-a len-b))
+         (res (%allocate-bignum len-res))
+         (negate-res (not (eq a-plusp b-plusp))))
     (declare (type bignum-index len-a len-b len-res))
     (dotimes (i len-a)
       (declare (type bignum-index i))
       (let ((carry-digit 0)
-	    (x (%bignum-ref a i))
-	    (k i))
-	(declare (type bignum-index k)
-		 (type bignum-element-type carry-digit x))
-	(dotimes (j len-b)
-	  (multiple-value-bind (big-carry res-digit)
-	      (%multiply-and-add x
-				 (%bignum-ref b j)
-				 (%bignum-ref res k)
-				 carry-digit)
-	    (declare (type bignum-element-type big-carry res-digit))
-	    (setf (%bignum-ref res k) res-digit)
-	    (setf carry-digit big-carry)
-	    (incf k)))
-	(setf (%bignum-ref res k) carry-digit)))
+            (x (%bignum-ref a i))
+            (k i))
+        (declare (type bignum-index k)
+                 (type bignum-element-type carry-digit x))
+        (dotimes (j len-b)
+          (multiple-value-bind (big-carry res-digit)
+              (%multiply-and-add x
+                                 (%bignum-ref b j)
+                                 (%bignum-ref res k)
+                                 carry-digit)
+            (declare (type bignum-element-type big-carry res-digit))
+            (setf (%bignum-ref res k) res-digit)
+            (setf carry-digit big-carry)
+            (incf k)))
+        (setf (%bignum-ref res k) carry-digit)))
     (when negate-res (negate-bignum-in-place res))
     (%normalize-bignum res len-res)))
 
 (defun multiply-bignum-and-fixnum (bignum fixnum)
   (declare (type bignum-type bignum) (type fixnum fixnum))
   (let* ((bignum-plus-p (%bignum-0-or-plusp bignum (%bignum-length bignum)))
-	 (fixnum-plus-p (not (minusp fixnum)))
-	 (bignum (if bignum-plus-p bignum (negate-bignum bignum)))
-	 (bignum-len (%bignum-length bignum))
-	 (fixnum (if fixnum-plus-p fixnum (- fixnum)))
-	 (result (%allocate-bignum (1+ bignum-len)))
-	 (carry-digit 0))
+         (fixnum-plus-p (not (minusp fixnum)))
+         (bignum (if bignum-plus-p bignum (negate-bignum bignum)))
+         (bignum-len (%bignum-length bignum))
+         (fixnum (if fixnum-plus-p fixnum (- fixnum)))
+         (result (%allocate-bignum (1+ bignum-len)))
+         (carry-digit 0))
     (declare (type bignum-type bignum result)
-	     (type bignum-index bignum-len)
-	     (type bignum-element-type fixnum carry-digit))
+             (type bignum-index bignum-len)
+             (type bignum-element-type fixnum carry-digit))
     (dotimes (index bignum-len)
       (declare (type bignum-index index))
       (multiple-value-bind (next-digit low)
-	  (%multiply-and-add (%bignum-ref bignum index) fixnum carry-digit)
-	(declare (type bignum-element-type next-digit low))
-	(setf carry-digit next-digit)
-	(setf (%bignum-ref result index) low)))
+          (%multiply-and-add (%bignum-ref bignum index) fixnum carry-digit)
+        (declare (type bignum-element-type next-digit low))
+        (setf carry-digit next-digit)
+        (setf (%bignum-ref result index) low)))
     (setf (%bignum-ref result bignum-len) carry-digit)
     (unless (eq bignum-plus-p fixnum-plus-p)
       (negate-bignum-in-place result))
@@ -441,76 +443,75 @@
 (defun multiply-fixnums (a b)
   (declare (fixnum a b))
   (let* ((a-minusp (minusp a))
-	 (b-minusp (minusp b)))
+         (b-minusp (minusp b)))
     (multiple-value-bind (high low)
-	(%multiply (if a-minusp (- a) a)
-		   (if b-minusp (- b) b))
+        (%multiply (if a-minusp (- a) a)
+                   (if b-minusp (- b) b))
       (declare (type bignum-element-type high low))
       (if (and (zerop high)
-	       (%digit-0-or-plusp low))
-	  (let ((low (sb!ext:truly-the (unsigned-byte 31)
-				       (%fixnum-digit-with-correct-sign low))))
-	    (if (eq a-minusp b-minusp)
-		low
-		(- low)))
-	  (let ((res (%allocate-bignum 2)))
-	    (%bignum-set res 0 low)
-	    (%bignum-set res 1 high)
-	    (unless (eq a-minusp b-minusp) (negate-bignum-in-place res))
-	    (%normalize-bignum res 2))))))
+               (%digit-0-or-plusp low))
+          (let ((low (sb!ext:truly-the (unsigned-byte #.(1- sb!vm:n-word-bits))
+                                       (%fixnum-digit-with-correct-sign low))))
+            (if (eq a-minusp b-minusp)
+                low
+                (- low)))
+          (let ((res (%allocate-bignum 2)))
+            (%bignum-set res 0 low)
+            (%bignum-set res 1 high)
+            (unless (eq a-minusp b-minusp) (negate-bignum-in-place res))
+            (%normalize-bignum res 2))))))
 
 ;;;; BIGNUM-REPLACE and WITH-BIGNUM-BUFFERS
 
 (eval-when (:compile-toplevel :execute)
 
 (sb!xc:defmacro bignum-replace (dest
-				src
-				&key
-				(start1 '0)
-				end1
-				(start2 '0)
-				end2
-				from-end)
+                                src
+                                &key
+                                (start1 '0)
+                                end1
+                                (start2 '0)
+                                end2
+                                from-end)
   (sb!int:once-only ((n-dest dest)
-		     (n-src src))
-    (let ((n-start1 (gensym))
-	  (n-end1 (gensym))
-	  (n-start2 (gensym))
-	  (n-end2 (gensym))
-	  (i1 (gensym))
-	  (i2 (gensym))
-	  (end1 (or end1 `(%bignum-length ,n-dest)))
-	  (end2 (or end2 `(%bignum-length ,n-src))))
-      (if from-end
-	  `(let ((,n-start1 ,start1)
-		 (,n-start2 ,start2))
-	     (do ((,i1 (1- ,end1) (1- ,i1))
-		  (,i2 (1- ,end2) (1- ,i2)))
-		 ((or (< ,i1 ,n-start1) (< ,i2 ,n-start2)))
-	       (declare (fixnum ,i1 ,i2))
-	       (%bignum-set ,n-dest ,i1
-			    (%bignum-ref ,n-src ,i2))))
-	  `(let ((,n-end1 ,end1)
-		 (,n-end2 ,end2))
-	     (do ((,i1 ,start1 (1+ ,i1))
-		  (,i2 ,start2 (1+ ,i2)))
-		 ((or (>= ,i1 ,n-end1) (>= ,i2 ,n-end2)))
-	       (declare (type bignum-index ,i1 ,i2))
-	       (%bignum-set ,n-dest ,i1
-			    (%bignum-ref ,n-src ,i2))))))))
+                     (n-src src))
+    (with-unique-names (n-start1 n-end1 n-start2 n-end2 i1 i2)
+      (let ((end1 (or end1 `(%bignum-length ,n-dest)))
+            (end2 (or end2 `(%bignum-length ,n-src))))
+        (if from-end
+            `(let ((,n-start1 ,start1)
+                   (,n-start2 ,start2))
+              (do ((,i1 (1- ,end1) (1- ,i1))
+                   (,i2 (1- ,end2) (1- ,i2)))
+                  ((or (< ,i1 ,n-start1) (< ,i2 ,n-start2)))
+                (declare (fixnum ,i1 ,i2))
+                (%bignum-set ,n-dest ,i1 (%bignum-ref ,n-src ,i2))))
+            (if (eql start1 start2)
+                `(let ((,n-end1 (min ,end1 ,end2)))
+                  (do ((,i1 ,start1 (1+ ,i1)))
+                      ((>= ,i1 ,n-end1))
+                    (declare (type bignum-index ,i1))
+                    (%bignum-set ,n-dest ,i1 (%bignum-ref ,n-src ,i1))))
+                `(let ((,n-end1 ,end1)
+                       (,n-end2 ,end2))
+                  (do ((,i1 ,start1 (1+ ,i1))
+                       (,i2 ,start2 (1+ ,i2)))
+                      ((or (>= ,i1 ,n-end1) (>= ,i2 ,n-end2)))
+                    (declare (type bignum-index ,i1 ,i2))
+                    (%bignum-set ,n-dest ,i1 (%bignum-ref ,n-src ,i2))))))))))
 
 (sb!xc:defmacro with-bignum-buffers (specs &body body)
   #!+sb-doc
   "WITH-BIGNUM-BUFFERS ({(var size [init])}*) Form*"
   (sb!int:collect ((binds)
-		   (inits))
+                   (inits))
     (dolist (spec specs)
       (let ((name (first spec))
-	    (size (second spec)))
-	(binds `(,name (%allocate-bignum ,size)))
-	(let ((init (third spec)))
-	  (when init
-	    (inits `(bignum-replace ,name ,init))))))
+            (size (second spec)))
+        (binds `(,name (%allocate-bignum ,size)))
+        (let ((init (third spec)))
+          (when init
+            (inits `(bignum-replace ,name ,init))))))
     `(let* ,(binds)
        ,@(inits)
        ,@body)))
@@ -519,105 +520,373 @@
 
 ;;;; GCD
 
-(defun bignum-gcd (a b)
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  ;; The asserts in the GCD implementation are way too expensive to
+  ;; check in normal use, and are disabled here.
+  (sb!xc:defmacro gcd-assert (&rest args)
+    (if nil
+        `(assert ,@args)))
+  ;; We'll be doing a lot of modular arithmetic.
+  (sb!xc:defmacro modularly (form)
+    `(logand all-ones-digit ,form)))
+
+;;; I'm not sure why I need this FTYPE declaration.  Compiled by the
+;;; target compiler, it can deduce the return type fine, but without
+;;; it, we pay a heavy price in BIGNUM-GCD when compiled by the
+;;; cross-compiler. -- CSR, 2004-07-19
+(declaim (ftype (sfunction (bignum-type bignum-index bignum-type bignum-index)
+                           (and unsigned-byte fixnum))
+                bignum-factors-of-two))
+(defun bignum-factors-of-two (a len-a b len-b)
+  (declare (type bignum-index len-a len-b) (type bignum-type a b))
+  (do ((i 0 (1+ i))
+       (end (min len-a len-b)))
+      ((= i end) (error "Unexpected zero bignums?"))
+    (declare (type bignum-index i end))
+    (let ((or-digits (%logior (%bignum-ref a i) (%bignum-ref b i))))
+      (unless (zerop or-digits)
+        (return (do ((j 0 (1+ j))
+                     (or-digits or-digits (%ashr or-digits 1)))
+                    ((oddp or-digits) (+ (* i digit-size) j))
+                  (declare (type (mod #.sb!vm:n-word-bits) j))))))))
+
+;;; Multiply a bignum buffer with a fixnum or a digit, storing the
+;;; result in another bignum buffer, and without using any
+;;; temporaries. Inlined to avoid boxing smallnum if it's actually a
+;;; digit. Needed by GCD, should possibly OAOO with
+;;; MULTIPLY-BIGNUM-AND-FIXNUM.
+(declaim (inline multiply-bignum-buffer-and-smallnum-to-buffer))
+(defun multiply-bignum-buffer-and-smallnum-to-buffer (bignum bignum-len
+                                                             smallnum res)
+  (declare (type bignum-type bignum))
+  (let* ((bignum-plus-p (%bignum-0-or-plusp bignum bignum-len))
+         (smallnum-plus-p (not (minusp smallnum)))
+         (smallnum (if smallnum-plus-p smallnum (- smallnum)))
+         (carry-digit 0))
+    (declare (type bignum-type bignum res)
+             (type bignum-index bignum-len)
+             (type bignum-element-type smallnum carry-digit))
+    (unless bignum-plus-p
+      (negate-bignum-buffer-in-place bignum bignum-len))
+    (dotimes (index bignum-len)
+      (declare (type bignum-index index))
+      (multiple-value-bind (next-digit low)
+          (%multiply-and-add (%bignum-ref bignum index)
+                             smallnum
+                             carry-digit)
+        (declare (type bignum-element-type next-digit low))
+        (setf carry-digit next-digit)
+        (setf (%bignum-ref res index) low)))
+    (setf (%bignum-ref res bignum-len) carry-digit)
+    (unless bignum-plus-p
+      (negate-bignum-buffer-in-place bignum bignum-len))
+    (let ((res-len (%normalize-bignum-buffer res (1+ bignum-len))))
+      (unless (eq bignum-plus-p smallnum-plus-p)
+        (negate-bignum-buffer-in-place res res-len))
+      res-len)))
+
+;;; Given U and V, return U / V mod 2^32. Implements the algorithm in the
+;;; paper, but uses some clever bit-twiddling nicked from Nickle to do it.
+(declaim (inline bmod))
+(defun bmod (u v)
+  (let ((ud (%bignum-ref u 0))
+        (vd (%bignum-ref v 0))
+        (umask 0)
+        (imask 1)
+        (m 0))
+    (declare (type (unsigned-byte #.sb!vm:n-word-bits) ud vd umask imask m))
+    (dotimes (i digit-size)
+      (setf umask (logior umask imask))
+      (when (logtest ud umask)
+        (setf ud (modularly (- ud vd)))
+        (setf m (modularly (logior m imask))))
+      (setf imask (modularly (ash imask 1)))
+      (setf vd (modularly (ash vd 1))))
+    m))
+
+(defun dmod (u u-len v v-len tmp1)
+  (loop while (> (bignum-buffer-integer-length u u-len)
+                 (+ (bignum-buffer-integer-length v v-len)
+                    digit-size))
+    do
+    (unless (zerop (%bignum-ref u 0))
+      (let* ((bmod (bmod u v))
+             (tmp1-len (multiply-bignum-buffer-and-smallnum-to-buffer v v-len
+                                                                      bmod
+                                                                      tmp1)))
+        (setf u-len (subtract-bignum-buffers u u-len
+                                             tmp1 tmp1-len
+                                             u))
+        (bignum-abs-buffer u u-len)))
+    (gcd-assert (zerop (%bignum-ref u 0)))
+    (setf u-len (bignum-buffer-ashift-right u u-len digit-size)))
+  (let* ((d (+ 1 (- (bignum-buffer-integer-length u u-len)
+                    (bignum-buffer-integer-length v v-len))))
+         (n (1- (ash 1 d))))
+    (declare (type (unsigned-byte #.(integer-length #.sb!vm:n-word-bits)) d)
+             (type (unsigned-byte #.sb!vm:n-word-bits) n))
+    (gcd-assert (>= d 0))
+    (when (logtest (%bignum-ref u 0) n)
+      (let ((tmp1-len
+             (multiply-bignum-buffer-and-smallnum-to-buffer v v-len
+                                                            (logand n (bmod u
+                                                                            v))
+                                                            tmp1)))
+        (setf u-len (subtract-bignum-buffers u u-len
+                                             tmp1 tmp1-len
+                                             u))
+        (bignum-abs-buffer u u-len)))
+    u-len))
+
+(defconstant lower-ones-digit (1- (ash 1 (truncate sb!vm:n-word-bits 2))))
+
+;;; Find D and N such that (LOGAND ALL-ONES-DIGIT (- (* D X) (* N Y))) is 0,
+;;; (< 0 N LOWER-ONES-DIGIT) and (< 0 (ABS D) LOWER-ONES-DIGIT).
+(defun reduced-ratio-mod (x y)
+  (let* ((c (bmod x y))
+         (n1 c)
+         (d1 1)
+         (n2 (modularly (1+ (modularly (lognot n1)))))
+         (d2 (modularly -1)))
+    (declare (type (unsigned-byte #.sb!vm:n-word-bits) n1 d1 n2 d2))
+    (loop while (> n2 (expt 2 (truncate digit-size 2))) do
+          (loop for i of-type (mod #.sb!vm:n-word-bits)
+                downfrom (- (integer-length n1) (integer-length n2))
+                while (>= n1 n2) do
+                (when (>= n1 (modularly (ash n2 i)))
+                  (psetf n1 (modularly (- n1 (modularly (ash n2 i))))
+                         d1 (modularly (- d1 (modularly (ash d2 i)))))))
+          (psetf n1 n2
+                 d1 d2
+                 n2 n1
+                 d2 d1))
+    (values n2 (if (>= d2 (expt 2 (1- digit-size)))
+                   (lognot (logand most-positive-fixnum (lognot d2)))
+                   (logand lower-ones-digit d2)))))
+
+
+(defun copy-bignum (a &optional (len (%bignum-length a)))
+  (let ((b (%allocate-bignum len)))
+    (bignum-replace b a)
+    (%bignum-set-length b len)
+    b))
+
+;;; Allocate a single word bignum that holds fixnum. This is useful when
+;;; we are trying to mix fixnum and bignum operands.
+#!-sb-fluid (declaim (inline make-small-bignum))
+(defun make-small-bignum (fixnum)
+  (let ((res (%allocate-bignum 1)))
+    (setf (%bignum-ref res 0) (%fixnum-to-digit fixnum))
+    res))
+
+;; When the larger number is less than this many bignum digits long, revert
+;; to old algorithm.
+(defparameter *accelerated-gcd-cutoff* 3)
+
+;;; Alternate between k-ary reduction with the help of
+;;; REDUCED-RATIO-MOD and digit modulus reduction via DMOD. Once the
+;;; arguments get small enough, drop through to BIGNUM-MOD-GCD (since
+;;; k-ary reduction can introduce spurious factors, which need to be
+;;; filtered out). Reference: Kenneth Weber, "The accelerated integer
+;;; GCD algorithm", ACM Transactions on Mathematical Software, volume
+;;; 21, number 1, March 1995, epp. 111-122.
+(defun bignum-gcd (u0 v0)
+  (declare (type bignum-type u0 v0))
+  (let* ((u1 (if (%bignum-0-or-plusp u0 (%bignum-length u0))
+                 u0
+                 (negate-bignum u0 nil)))
+         (v1 (if (%bignum-0-or-plusp v0 (%bignum-length v0))
+                 v0
+                 (negate-bignum v0 nil))))
+    (if (zerop v1)
+        (return-from bignum-gcd u1))
+    (when (> u1 v1)
+      (rotatef u1 v1))
+    (let ((n (mod v1 u1)))
+      (setf v1 (if (fixnump n)
+                   (make-small-bignum n)
+                   n)))
+    (if (and (= 1 (%bignum-length v1))
+             (zerop (%bignum-ref v1 0)))
+        (return-from bignum-gcd (%normalize-bignum u1
+                                                   (%bignum-length u1))))
+    (let* ((buffer-len (+ 2 (%bignum-length u1)))
+           (u (%allocate-bignum buffer-len))
+           (u-len (%bignum-length u1))
+           (v (%allocate-bignum buffer-len))
+           (v-len (%bignum-length v1))
+           (tmp1 (%allocate-bignum buffer-len))
+           (tmp1-len 0)
+           (tmp2 (%allocate-bignum buffer-len))
+           (tmp2-len 0)
+           (factors-of-two
+            (bignum-factors-of-two u1 (%bignum-length u1)
+                                   v1 (%bignum-length v1))))
+      (declare (type (or null bignum-index)
+                     buffer-len u-len v-len tmp1-len tmp2-len))
+      (bignum-replace u u1)
+      (bignum-replace v v1)
+      (setf u-len
+            (make-gcd-bignum-odd u
+                                 (bignum-buffer-ashift-right u u-len
+                                                             factors-of-two)))
+      (setf v-len
+            (make-gcd-bignum-odd v
+                                 (bignum-buffer-ashift-right v v-len
+                                                             factors-of-two)))
+      (loop until (or (< u-len *accelerated-gcd-cutoff*)
+                      (not v-len)
+                      (zerop v-len)
+                      (and (= 1 v-len)
+                           (zerop (%bignum-ref v 0))))
+        do
+        (gcd-assert (= buffer-len (%bignum-length u)
+                       (%bignum-length v)
+                       (%bignum-length tmp1)
+                       (%bignum-length tmp2)))
+        (if (> (bignum-buffer-integer-length u u-len)
+               (+ #.(truncate sb!vm:n-word-bits 4)
+                  (bignum-buffer-integer-length v v-len)))
+            (setf u-len (dmod u u-len
+                              v v-len
+                              tmp1))
+            (multiple-value-bind (n d) (reduced-ratio-mod u v)
+              (setf tmp1-len
+                    (multiply-bignum-buffer-and-smallnum-to-buffer v v-len
+                                                                   n tmp1))
+              (setf tmp2-len
+                    (multiply-bignum-buffer-and-smallnum-to-buffer u u-len
+                                                                   d tmp2))
+              (gcd-assert (= (copy-bignum tmp2 tmp2-len)
+                             (* (copy-bignum u u-len) d)))
+              (gcd-assert (= (copy-bignum tmp1 tmp1-len)
+                             (* (copy-bignum v v-len) n)))
+              (setf u-len
+                    (subtract-bignum-buffers-with-len tmp1 tmp1-len
+                                                      tmp2 tmp2-len
+                                                      u
+                                                      (1+ (max tmp1-len
+                                                               tmp2-len))))
+              (gcd-assert (or (zerop (- (copy-bignum tmp1 tmp1-len)
+                                        (copy-bignum tmp2 tmp2-len)))
+                              (= (copy-bignum u u-len)
+                                 (- (copy-bignum tmp1 tmp1-len)
+                                    (copy-bignum tmp2 tmp2-len)))))
+              (bignum-abs-buffer u u-len)
+              (gcd-assert (zerop (modularly u)))))
+        (setf u-len (make-gcd-bignum-odd u u-len))
+        (rotatef u v)
+        (rotatef u-len v-len))
+      (bignum-abs-buffer u u-len)
+      (setf u (copy-bignum u u-len))
+      (let ((n (bignum-mod-gcd v1 u)))
+        (ash (bignum-mod-gcd u1 (if (fixnump n)
+                                    (make-small-bignum n)
+                                    n))
+             factors-of-two)))))
+
+(defun bignum-mod-gcd (a b)
   (declare (type bignum-type a b))
-  (let* ((a (if (%bignum-0-or-plusp a (%bignum-length a))
-		a
-		(negate-bignum a nil)))
-	 (b (if (%bignum-0-or-plusp b (%bignum-length b))
-		b
-		(negate-bignum b nil)))
-	 (len-a (%bignum-length a))
-	 (len-b (%bignum-length b)))
-      (declare (type bignum-index len-a len-b))
+  (when (< a b)
+    (rotatef a b))
+  ;; While the length difference of A and B is sufficiently large,
+  ;; reduce using MOD (slowish, but it should equalize the sizes of
+  ;; A and B pretty quickly). After that, use the binary GCD
+  ;; algorithm to handle the rest.
+  (loop until (and (= (%bignum-length b) 1) (zerop (%bignum-ref b 0))) do
+        (when (<= (%bignum-length a) (1+ (%bignum-length b)))
+          (return-from bignum-mod-gcd (bignum-binary-gcd a b)))
+        (let ((rem (mod a b)))
+          (if (fixnump rem)
+              (setf a (make-small-bignum rem))
+              (setf a rem))
+          (rotatef a b)))
+  (if (= (%bignum-length a) 1)
+      (%normalize-bignum a 1)
+      a))
+
+(defun bignum-binary-gcd (a b)
+  (declare (type bignum-type a b))
+  (let* ((len-a (%bignum-length a))
+         (len-b (%bignum-length b)))
+    (declare (type bignum-index len-a len-b))
     (with-bignum-buffers ((a-buffer len-a a)
-			  (b-buffer len-b b)
-			  (res-buffer (max len-a len-b)))
+                          (b-buffer len-b b)
+                          (res-buffer (max len-a len-b)))
       (let* ((factors-of-two
-	      (bignum-factors-of-two a-buffer len-a
-				     b-buffer len-b))
-	     (len-a (make-gcd-bignum-odd
-		     a-buffer
-		     (bignum-buffer-ashift-right a-buffer len-a
-						 factors-of-two)))
-	     (len-b (make-gcd-bignum-odd
-		     b-buffer
-		     (bignum-buffer-ashift-right b-buffer len-b
-						 factors-of-two))))
-	(declare (type bignum-index len-a len-b))
-	(let ((x a-buffer)
-	      (len-x len-a)
-	      (y b-buffer)
-	      (len-y len-b)
-	      (z res-buffer))
-	  (loop
-	    (multiple-value-bind (u v len-v r len-r)
-		(bignum-gcd-order-and-subtract x len-x y len-y z)
-	      (declare (type bignum-index len-v len-r))
-	      (when (and (= len-r 1) (zerop (%bignum-ref r 0)))
-		(if (zerop factors-of-two)
-		    (let ((ret (%allocate-bignum len-v)))
-		      (dotimes (i len-v)
-			(setf (%bignum-ref ret i) (%bignum-ref v i)))
-		      (return (%normalize-bignum ret len-v)))
-		    (return (bignum-ashift-left v factors-of-two len-v))))
-	      (setf x v  len-x len-v)
-	      (setf y r  len-y (make-gcd-bignum-odd r len-r))
-	      (setf z u))))))))
+              (bignum-factors-of-two a-buffer len-a
+                                     b-buffer len-b))
+             (len-a (make-gcd-bignum-odd
+                     a-buffer
+                     (bignum-buffer-ashift-right a-buffer len-a
+                                                 factors-of-two)))
+             (len-b (make-gcd-bignum-odd
+                     b-buffer
+                     (bignum-buffer-ashift-right b-buffer len-b
+                                                 factors-of-two))))
+        (declare (type bignum-index len-a len-b))
+        (let ((x a-buffer)
+              (len-x len-a)
+              (y b-buffer)
+              (len-y len-b)
+              (z res-buffer))
+          (loop
+            (multiple-value-bind (u v len-v r len-r)
+                (bignum-gcd-order-and-subtract x len-x y len-y z)
+              (declare (type bignum-index len-v len-r))
+              (when (and (= len-r 1) (zerop (%bignum-ref r 0)))
+                (if (zerop factors-of-two)
+                    (let ((ret (%allocate-bignum len-v)))
+                      (dotimes (i len-v)
+                        (setf (%bignum-ref ret i) (%bignum-ref v i)))
+                      (return (%normalize-bignum ret len-v)))
+                    (return (bignum-ashift-left v factors-of-two len-v))))
+              (setf x v  len-x len-v)
+              (setf y r  len-y (make-gcd-bignum-odd r len-r))
+              (setf z u))))))))
 
 (defun bignum-gcd-order-and-subtract (a len-a b len-b res)
   (declare (type bignum-index len-a len-b) (type bignum-type a b))
   (cond ((= len-a len-b)
-	 (do ((i (1- len-a) (1- i)))
-	     ((= i -1)
-	      (setf (%bignum-ref res 0) 0)
-	      (values a b len-b res 1))
-	   (let ((a-digit (%bignum-ref a i))
-		 (b-digit (%bignum-ref b i)))
-	     (cond ((%digit-compare a-digit b-digit))
-		   ((%digit-greater a-digit b-digit)
-		    (return
-		     (values a b len-b res
-			     (subtract-bignum-buffers a len-a b len-b res))))
-		   (t
-		    (return
-		     (values b a len-a res
-			     (subtract-bignum-buffers b len-b
-						      a len-a
-						      res))))))))
-	((> len-a len-b)
-	 (values a b len-b res
-		 (subtract-bignum-buffers a len-a b len-b res)))
-	(t
-	 (values b a len-a res
-		 (subtract-bignum-buffers b len-b a len-a res)))))
+         (do ((i (1- len-a) (1- i)))
+             ((= i -1)
+              (setf (%bignum-ref res 0) 0)
+              (values a b len-b res 1))
+           (let ((a-digit (%bignum-ref a i))
+                 (b-digit (%bignum-ref b i)))
+             (cond ((%digit-compare a-digit b-digit))
+                   ((%digit-greater a-digit b-digit)
+                    (return
+                     (values a b len-b res
+                             (subtract-bignum-buffers a len-a b len-b
+                                                      res))))
+                   (t
+                    (return
+                     (values b a len-a res
+                             (subtract-bignum-buffers b len-b
+                                                      a len-a
+                                                      res))))))))
+        ((> len-a len-b)
+         (values a b len-b res
+                 (subtract-bignum-buffers a len-a b len-b res)))
+        (t
+         (values b a len-a res
+                 (subtract-bignum-buffers b len-b a len-a res)))))
 
 (defun make-gcd-bignum-odd (a len-a)
   (declare (type bignum-type a) (type bignum-index len-a))
   (dotimes (index len-a)
     (declare (type bignum-index index))
     (do ((digit (%bignum-ref a index) (%ashr digit 1))
-	 (increment 0 (1+ increment)))
-	((zerop digit))
-      (declare (type (mod 32) increment))
+         (increment 0 (1+ increment)))
+        ((zerop digit))
+      (declare (type (mod #.sb!vm:n-word-bits) increment))
       (when (oddp digit)
-	(return-from make-gcd-bignum-odd
-		     (bignum-buffer-ashift-right a len-a
-						 (+ (* index digit-size)
-						    increment)))))))
+        (return-from make-gcd-bignum-odd
+                     (bignum-buffer-ashift-right a len-a
+                                                 (+ (* index digit-size)
+                                                    increment)))))))
 
-(defun bignum-factors-of-two (a len-a b len-b)
-  (declare (type bignum-index len-a len-b) (type bignum-type a))
-  (do ((i 0 (1+ i))
-       (end (min len-a len-b)))
-      ((= i end) (error "Unexpected zero bignums?"))
-    (declare (type bignum-index i end))
-    (let ((or-digits (%logior (%bignum-ref a i) (%bignum-ref b i))))
-      (unless (zerop or-digits)
-	(return (do ((j 0 (1+ j))
-		     (or-digits or-digits (%ashr or-digits 1)))
-		    ((oddp or-digits) (+ (* i digit-size) j))
-		  (declare (type (mod 32) j))))))))
 
 ;;;; negation
 
@@ -625,34 +894,30 @@
 
 ;;; This negates bignum-len digits of bignum, storing the resulting digits into
 ;;; result (possibly EQ to bignum) and returning whatever end-carry there is.
-(sb!xc:defmacro bignum-negate-loop (bignum
-				    bignum-len
-				    &optional (result nil resultp))
-  (let ((carry (gensym))
-	(end (gensym))
-	(value (gensym))
-	(last (gensym)))
+(sb!xc:defmacro bignum-negate-loop
+    (bignum bignum-len &optional (result nil resultp))
+  (with-unique-names (carry end value last)
     `(let* (,@(if (not resultp) `(,last))
-	    (,carry
-	     (multiple-value-bind (,value ,carry)
-		 (%add-with-carry (%lognot (%bignum-ref ,bignum 0)) 1 0)
-	       ,(if resultp
-		    `(setf (%bignum-ref ,result 0) ,value)
-		    `(setf ,last ,value))
-	       ,carry))
-	    (i 1)
-	    (,end ,bignum-len))
+            (,carry
+             (multiple-value-bind (,value ,carry)
+                 (%add-with-carry (%lognot (%bignum-ref ,bignum 0)) 1 0)
+               ,(if resultp
+                    `(setf (%bignum-ref ,result 0) ,value)
+                    `(setf ,last ,value))
+               ,carry))
+            (i 1)
+            (,end ,bignum-len))
        (declare (type bit ,carry)
-		(type bignum-index i ,end))
+                (type bignum-index i ,end))
        (loop
-	 (when (= i ,end) (return))
-	 (multiple-value-bind (,value temp)
-	     (%add-with-carry (%lognot (%bignum-ref ,bignum i)) 0 ,carry)
-	   ,(if resultp
-		`(setf (%bignum-ref ,result i) ,value)
-		`(setf ,last ,value))
-	   (setf ,carry temp))
-	 (incf i))
+         (when (= i ,end) (return))
+         (multiple-value-bind (,value temp)
+             (%add-with-carry (%lognot (%bignum-ref ,bignum i)) 0 ,carry)
+           ,(if resultp
+                `(setf (%bignum-ref ,result i) ,value)
+                `(setf ,last ,value))
+           (setf ,carry temp))
+         (incf i))
        ,(if resultp carry `(values ,carry ,last)))))
 
 ) ; EVAL-WHEN
@@ -662,26 +927,32 @@
 (defun negate-bignum (x &optional (fully-normalize t))
   (declare (type bignum-type x))
   (let* ((len-x (%bignum-length x))
-	 (len-res (1+ len-x))
-	 (res (%allocate-bignum len-res)))
+         (len-res (1+ len-x))
+         (res (%allocate-bignum len-res)))
     (declare (type bignum-index len-x len-res)) ;Test len-res for range?
     (let ((carry (bignum-negate-loop x len-x res)))
       (setf (%bignum-ref res len-x)
-	    (%add-with-carry (%lognot (%sign-digit x len-x)) 0 carry)))
+            (%add-with-carry (%lognot (%sign-digit x len-x)) 0 carry)))
     (if fully-normalize
-	(%normalize-bignum res len-res)
-	(%mostly-normalize-bignum res len-res))))
+        (%normalize-bignum res len-res)
+        (%mostly-normalize-bignum res len-res))))
 
 ;;; This assumes bignum is positive; that is, the result of negating it will
 ;;; stay in the provided allocated bignum.
-(defun negate-bignum-in-place (bignum)
-  (bignum-negate-loop bignum (%bignum-length bignum) bignum)
+(defun negate-bignum-buffer-in-place (bignum bignum-len)
+  (bignum-negate-loop bignum bignum-len bignum)
   bignum)
+
+(defun negate-bignum-in-place (bignum)
+  (declare (inline negate-bignum-buffer-in-place))
+  (negate-bignum-buffer-in-place bignum (%bignum-length bignum)))
+
+(defun bignum-abs-buffer (bignum len)
+  (unless (%bignum-0-or-plusp bignum len)
+    (negate-bignum-buffer-in-place bignum len)))
 
 ;;;; shifting
 
-(defconstant all-ones-digit #xFFFFFFFF)
-
 (eval-when (:compile-toplevel :execute)
 
 ;;; This macro is used by BIGNUM-ASHIFT-RIGHT, BIGNUM-BUFFER-ASHIFT-RIGHT, and
@@ -697,26 +968,25 @@
 ;;; digit from high bits of the i'th source digit and the start-pos number of
 ;;; bits from the i+1'th source digit.
 (sb!xc:defmacro shift-right-unaligned (source
-				       start-digit
-				       start-pos
-				       res-len-form
-				       termination
-				       &optional result)
+                                       start-digit
+                                       start-pos
+                                       res-len-form
+                                       termination
+                                       &optional result)
   `(let* ((high-bits-in-first-digit (- digit-size ,start-pos))
-	  (res-len ,res-len-form)
-	  (res-len-1 (1- res-len))
-	  ,@(if result `((,result (%allocate-bignum res-len)))))
+          (res-len ,res-len-form)
+          (res-len-1 (1- res-len))
+          ,@(if result `((,result (%allocate-bignum res-len)))))
      (declare (type bignum-index res-len res-len-1))
-     (do ((i ,start-digit i+1)
-	  (i+1 (1+ ,start-digit) (1+ i+1))
-	  (j 0 (1+ j)))
-	 ,termination
-       (declare (type bignum-index i i+1 j))
+     (do ((i ,start-digit (1+ i))
+          (j 0 (1+ j)))
+         ,termination
+       (declare (type bignum-index i j))
        (setf (%bignum-ref ,(if result result source) j)
-	     (%logior (%digit-logical-shift-right (%bignum-ref ,source i)
-						  ,start-pos)
-		      (%ashl (%bignum-ref ,source i+1)
-			     high-bits-in-first-digit))))))
+             (%logior (%digit-logical-shift-right (%bignum-ref ,source i)
+                                                  ,start-pos)
+                      (%ashl (%bignum-ref ,source (1+ i))
+                             high-bits-in-first-digit))))))
 
 ) ; EVAL-WHEN
 
@@ -730,40 +1000,40 @@
 ;;; locals established by the macro.
 (defun bignum-ashift-right (bignum count)
   (declare (type bignum-type bignum)
-	   (type unsigned-byte count))
+           (type unsigned-byte count))
   (let ((bignum-len (%bignum-length bignum)))
     (declare (type bignum-index bignum-len))
     (cond ((fixnump count)
-	   (multiple-value-bind (digits n-bits) (truncate count digit-size)
-	     (declare (type bignum-index digits))
-	     (cond
-	      ((>= digits bignum-len)
-	       (if (%bignum-0-or-plusp bignum bignum-len) 0 -1))
-	      ((zerop n-bits)
-	       (bignum-ashift-right-digits bignum digits))
-	      (t
-	       (shift-right-unaligned bignum digits n-bits (- bignum-len digits)
-				      ((= j res-len-1)
-				       (setf (%bignum-ref res j)
-					     (%ashr (%bignum-ref bignum i) n-bits))
-				       (%normalize-bignum res res-len))
-				      res)))))
-	  ((> count bignum-len)
-	   0)
-	   ;; Since a FIXNUM should be big enough to address anything in
-	   ;; memory, including arrays of bits, and since arrays of bits
-	   ;; take up about the same space as corresponding fixnums, there
-	   ;; should be no way that we fall through to this case: any shift
-	   ;; right by a bignum should give zero. But let's check anyway:
-	  (t (error "bignum overflow: can't shift right by ~S" count)))))
+           (multiple-value-bind (digits n-bits) (truncate count digit-size)
+             (declare (type bignum-index digits))
+             (cond
+              ((>= digits bignum-len)
+               (if (%bignum-0-or-plusp bignum bignum-len) 0 -1))
+              ((zerop n-bits)
+               (bignum-ashift-right-digits bignum digits))
+              (t
+               (shift-right-unaligned bignum digits n-bits (- bignum-len digits)
+                                      ((= j res-len-1)
+                                       (setf (%bignum-ref res j)
+                                             (%ashr (%bignum-ref bignum i) n-bits))
+                                       (%normalize-bignum res res-len))
+                                      res)))))
+          ((> count bignum-len)
+           (if (%bignum-0-or-plusp bignum bignum-len) 0 -1))
+           ;; Since a FIXNUM should be big enough to address anything in
+           ;; memory, including arrays of bits, and since arrays of bits
+           ;; take up about the same space as corresponding fixnums, there
+           ;; should be no way that we fall through to this case: any shift
+           ;; right by a bignum should give zero. But let's check anyway:
+          (t (error "bignum overflow: can't shift right by ~S" count)))))
 
 (defun bignum-ashift-right-digits (bignum digits)
   (declare (type bignum-type bignum)
-	   (type bignum-index digits))
+           (type bignum-index digits))
   (let* ((res-len (- (%bignum-length bignum) digits))
-	 (res (%allocate-bignum res-len)))
+         (res (%allocate-bignum res-len)))
     (declare (type bignum-index res-len)
-	     (type bignum-type res))
+             (type bignum-type res))
     (bignum-replace res bignum :start2 digits)
     (%normalize-bignum res res-len)))
 
@@ -781,15 +1051,15 @@
     (cond
      ((zerop n-bits)
       (let ((new-end (- bignum-len digits)))
-	(bignum-replace bignum bignum :end1 new-end :start2 digits
-			:end2 bignum-len)
-	(%normalize-bignum-buffer bignum new-end)))
+        (bignum-replace bignum bignum :end1 new-end :start2 digits
+                        :end2 bignum-len)
+        (%normalize-bignum-buffer bignum new-end)))
      (t
       (shift-right-unaligned bignum digits n-bits (- bignum-len digits)
-			     ((= j res-len-1)
-			      (setf (%bignum-ref bignum j)
-				    (%ashr (%bignum-ref bignum i) n-bits))
-			      (%normalize-bignum-buffer bignum res-len)))))))
+                             ((= j res-len-1)
+                              (setf (%bignum-ref bignum j)
+                                    (%ashr (%bignum-ref bignum i) n-bits))
+                              (%normalize-bignum-buffer bignum res-len)))))))
 
 ;;; This handles shifting a bignum buffer to provide fresh bignum data for some
 ;;; internal routines. We know bignum is safe when called with bignum-len.
@@ -799,17 +1069,17 @@
 ;;; branch handles the general case.
 (defun bignum-ashift-left (bignum x &optional bignum-len)
   (declare (type bignum-type bignum)
-	   (type unsigned-byte x)
-	   (type (or null bignum-index) bignum-len))
+           (type unsigned-byte x)
+           (type (or null bignum-index) bignum-len))
   (if (fixnump x)
     (multiple-value-bind (digits n-bits) (truncate x digit-size)
       (let* ((bignum-len (or bignum-len (%bignum-length bignum)))
-	     (res-len (+ digits bignum-len 1)))
-	(when (> res-len maximum-bignum-length)
-	  (error "can't represent result of left shift"))
-	(if (zerop n-bits)
-	  (bignum-ashift-left-digits bignum bignum-len digits)
-	  (bignum-ashift-left-unaligned bignum digits n-bits res-len))))
+             (res-len (+ digits bignum-len 1)))
+        (when (> res-len maximum-bignum-length)
+          (error "can't represent result of left shift"))
+        (if (zerop n-bits)
+          (bignum-ashift-left-digits bignum bignum-len digits)
+          (bignum-ashift-left-unaligned bignum digits n-bits res-len))))
     ;; Left shift by a number too big to be represented as a fixnum
     ;; would exceed our memory capacity, since a fixnum is big enough
     ;; to index any array, including a bit array.
@@ -818,10 +1088,10 @@
 (defun bignum-ashift-left-digits (bignum bignum-len digits)
   (declare (type bignum-index bignum-len digits))
   (let* ((res-len (+ bignum-len digits))
-	 (res (%allocate-bignum res-len)))
+         (res (%allocate-bignum res-len)))
     (declare (type bignum-index res-len))
     (bignum-replace res bignum :start1 digits :end1 res-len :end2 bignum-len
-		    :from-end t)
+                    :from-end t)
     res))
 
 ;;; BIGNUM-TRUNCATE uses this to store into a bignum buffer by supplying res.
@@ -834,29 +1104,28 @@
 ;;; first non-zero result digit, digits. We also grab some left over high
 ;;; bits from the last digit of bignum.
 (defun bignum-ashift-left-unaligned (bignum digits n-bits res-len
-				     &optional (res nil resp))
+                                     &optional (res nil resp))
   (declare (type bignum-index digits res-len)
-	   (type (mod #.digit-size) n-bits))
+           (type (mod #.digit-size) n-bits))
   (let* ((remaining-bits (- digit-size n-bits))
-	 (res-len-1 (1- res-len))
-	 (res (or res (%allocate-bignum res-len))))
+         (res-len-1 (1- res-len))
+         (res (or res (%allocate-bignum res-len))))
     (declare (type bignum-index res-len res-len-1))
-    (do ((i 0 i+1)
-	 (i+1 1 (1+ i+1))
-	 (j (1+ digits) (1+ j)))
-	((= j res-len-1)
-	 (setf (%bignum-ref res digits)
-	       (%ashl (%bignum-ref bignum 0) n-bits))
-	 (setf (%bignum-ref res j)
-	       (%ashr (%bignum-ref bignum i) remaining-bits))
-	 (if resp
-	     (%normalize-bignum-buffer res res-len)
-	     (%normalize-bignum res res-len)))
-      (declare (type bignum-index i i+1 j))
+    (do ((i 0 (1+ i))
+         (j (1+ digits) (1+ j)))
+        ((= j res-len-1)
+         (setf (%bignum-ref res digits)
+               (%ashl (%bignum-ref bignum 0) n-bits))
+         (setf (%bignum-ref res j)
+               (%ashr (%bignum-ref bignum i) remaining-bits))
+         (if resp
+             (%normalize-bignum-buffer res res-len)
+             (%normalize-bignum res res-len)))
+      (declare (type bignum-index i j))
       (setf (%bignum-ref res j)
-	    (%logior (%digit-logical-shift-right (%bignum-ref bignum i)
-						 remaining-bits)
-		     (%ashl (%bignum-ref bignum i+1) n-bits))))))
+            (%logior (%digit-logical-shift-right (%bignum-ref bignum i)
+                                                 remaining-bits)
+                     (%ashl (%bignum-ref bignum (1+ i)) n-bits))))))
 
 ;;;; relational operators
 
@@ -871,27 +1140,27 @@
 (defun bignum-compare (a b)
   (declare (type bignum-type a b))
   (let* ((len-a (%bignum-length a))
-	 (len-b (%bignum-length b))
-	 (a-plusp (%bignum-0-or-plusp a len-a))
-	 (b-plusp (%bignum-0-or-plusp b len-b)))
+         (len-b (%bignum-length b))
+         (a-plusp (%bignum-0-or-plusp a len-a))
+         (b-plusp (%bignum-0-or-plusp b len-b)))
     (declare (type bignum-index len-a len-b))
     (cond ((not (eq a-plusp b-plusp))
-	   (if a-plusp 1 -1))
-	  ((= len-a len-b)
-	   (do ((i (1- len-a) (1- i)))
-	       (())
-	     (declare (type bignum-index i))
-	     (let ((a-digit (%bignum-ref a i))
-		   (b-digit (%bignum-ref b i)))
-	       (declare (type bignum-element-type a-digit b-digit))
-	       (when (%digit-greater a-digit b-digit)
-		 (return 1))
-	       (when (%digit-greater b-digit a-digit)
-		 (return -1)))
-	     (when (zerop i) (return 0))))
-	  ((> len-a len-b)
-	   (if a-plusp 1 -1))
-	  (t (if a-plusp -1 1)))))
+           (if a-plusp 1 -1))
+          ((= len-a len-b)
+           (do ((i (1- len-a) (1- i)))
+               (())
+             (declare (type bignum-index i))
+             (let ((a-digit (%bignum-ref a i))
+                   (b-digit (%bignum-ref b i)))
+               (declare (type bignum-element-type a-digit b-digit))
+               (when (%digit-greater a-digit b-digit)
+                 (return 1))
+               (when (%digit-greater b-digit a-digit)
+                 (return -1)))
+             (when (zerop i) (return 0))))
+          ((> len-a len-b)
+           (if a-plusp 1 -1))
+          (t (if a-plusp -1 1)))))
 
 ;;;; float conversion
 
@@ -901,27 +1170,28 @@
   (declare (fixnum exp))
   (declare (optimize #-sb-xc-host (sb!ext:inhibit-warnings 3)))
   (let ((res (dpb exp
-		  sb!vm:single-float-exponent-byte
-		  (logandc2 (sb!ext:truly-the (unsigned-byte 31)
-					      (%bignum-ref bits 1))
-			    sb!vm:single-float-hidden-bit))))
+                  sb!vm:single-float-exponent-byte
+                  (logandc2 (logand #xffffffff
+                                    (%bignum-ref bits 1))
+                            sb!vm:single-float-hidden-bit))))
     (make-single-float
      (if plusp
-	 res
-	 (logior res (ash -1 sb!vm:float-sign-shift))))))
+         res
+         (logior res (ash -1 sb!vm:float-sign-shift))))))
 (defun double-float-from-bits (bits exp plusp)
   (declare (fixnum exp))
   (declare (optimize #-sb-xc-host (sb!ext:inhibit-warnings 3)))
   (let ((hi (dpb exp
-		 sb!vm:double-float-exponent-byte
-		 (logandc2 (sb!ext:truly-the (unsigned-byte 31)
-					     (%bignum-ref bits 2))
-			   sb!vm:double-float-hidden-bit))))
-    (make-double-float
-     (if plusp
-	 hi
-	 (logior hi (ash -1 sb!vm:float-sign-shift)))
-     (%bignum-ref bits 1))))
+                 sb!vm:double-float-exponent-byte
+                 (logandc2 (ecase sb!vm::n-word-bits
+                             (32 (%bignum-ref bits 2))
+                             (64 (ash (%bignum-ref bits 1) -32)))
+                           sb!vm:double-float-hidden-bit)))
+        (lo (logand #xffffffff (%bignum-ref bits 1))))
+    (make-double-float (if plusp
+                           hi
+                           (logior hi (ash -1 sb!vm:float-sign-shift)))
+                       lo)))
 #!+(and long-float x86)
 (defun long-float-from-bits (bits exp plusp)
   (declare (fixnum exp))
@@ -937,113 +1207,117 @@
 ;;; approximation.
 (defun bignum-to-float (bignum format)
   (let* ((plusp (bignum-plus-p bignum))
-	 (x (if plusp bignum (negate-bignum bignum)))
-	 (len (bignum-integer-length x))
-	 (digits (float-format-digits format))
-	 (keep (+ digits digit-size))
-	 (shift (- keep len))
-	 (shifted (if (minusp shift)
-		      (bignum-ashift-right x (- shift))
-		      (bignum-ashift-left x shift)))
-	 (low (%bignum-ref shifted 0))
-	 (round-bit (ash 1 (1- digit-size))))
+         (x (if plusp bignum (negate-bignum bignum)))
+         (len (bignum-integer-length x))
+         (digits (float-format-digits format))
+         (keep (+ digits digit-size))
+         (shift (- keep len))
+         (shifted (if (minusp shift)
+                      (bignum-ashift-right x (- shift))
+                      (bignum-ashift-left x shift)))
+         (low (%bignum-ref shifted 0))
+         (round-bit (ash 1 (1- digit-size))))
     (declare (type bignum-index len digits keep) (fixnum shift))
     (labels ((round-up ()
-	       (let ((rounded (add-bignums shifted round-bit)))
-		 (if (> (integer-length rounded) keep)
-		     (float-from-bits (bignum-ashift-right rounded 1)
-				      (1+ len))
-		     (float-from-bits rounded len))))
-	     (float-from-bits (bits len)
-	       (declare (type bignum-index len))
-	       (ecase format
-		 (single-float
-		  (single-float-from-bits
-		   bits
-		   (check-exponent len sb!vm:single-float-bias
-				   sb!vm:single-float-normal-exponent-max)
-		   plusp))
-		 (double-float
-		  (double-float-from-bits
-		   bits
-		   (check-exponent len sb!vm:double-float-bias
-				   sb!vm:double-float-normal-exponent-max)
-		   plusp))
-		 #!+long-float
-		 (long-float
-		  (long-float-from-bits
-		   bits
-		   (check-exponent len sb!vm:long-float-bias
-				   sb!vm:long-float-normal-exponent-max)
-		   plusp))))
-	     (check-exponent (exp bias max)
-	       (declare (type bignum-index len))
-	       (let ((exp (+ exp bias)))
-		 (when (> exp max)
-		   ;; Why a SIMPLE-TYPE-ERROR? Well, this is mainly
-		   ;; called by COERCE, which requires an error of
-		   ;; TYPE-ERROR if the conversion can't happen
-		   ;; (except in certain circumstances when we are
-		   ;; coercing to a FUNCTION) -- CSR, 2002-09-18
-		   (error 'simple-type-error
-			  :format-control "Too large to be represented as a ~S:~%  ~S"
-			  :format-arguments (list format x)
-			  :expected-type format
-			  :datum x))
-		 exp)))
+               (let ((rounded (add-bignums shifted round-bit)))
+                 (if (> (integer-length rounded) keep)
+                     (float-from-bits (bignum-ashift-right rounded 1)
+                                      (1+ len))
+                     (float-from-bits rounded len))))
+             (float-from-bits (bits len)
+               (declare (type bignum-index len))
+               (ecase format
+                 (single-float
+                  (single-float-from-bits
+                   bits
+                   (check-exponent len sb!vm:single-float-bias
+                                   sb!vm:single-float-normal-exponent-max)
+                   plusp))
+                 (double-float
+                  (double-float-from-bits
+                   bits
+                   (check-exponent len sb!vm:double-float-bias
+                                   sb!vm:double-float-normal-exponent-max)
+                   plusp))
+                 #!+long-float
+                 (long-float
+                  (long-float-from-bits
+                   bits
+                   (check-exponent len sb!vm:long-float-bias
+                                   sb!vm:long-float-normal-exponent-max)
+                   plusp))))
+             (check-exponent (exp bias max)
+               (declare (type bignum-index len))
+               (let ((exp (+ exp bias)))
+                 (when (> exp max)
+                   ;; Why a SIMPLE-TYPE-ERROR? Well, this is mainly
+                   ;; called by COERCE, which requires an error of
+                   ;; TYPE-ERROR if the conversion can't happen
+                   ;; (except in certain circumstances when we are
+                   ;; coercing to a FUNCTION) -- CSR, 2002-09-18
+                   (error 'simple-type-error
+                          :format-control "Too large to be represented as a ~S:~%  ~S"
+                          :format-arguments (list format x)
+                          :expected-type format
+                          :datum x))
+                 exp)))
 
     (cond
      ;; Round down if round bit is 0.
-     ((zerop (logand round-bit low))
+     ((not (logtest round-bit low))
       (float-from-bits shifted len))
      ;; If only round bit is set, then round to even.
      ((and (= low round-bit)
-	   (dotimes (i (- (%bignum-length x) (ceiling keep digit-size))
-		       t)
-	     (unless (zerop (%bignum-ref x i)) (return nil))))
+           (dotimes (i (- (%bignum-length x) (ceiling keep digit-size))
+                       t)
+             (unless (zerop (%bignum-ref x i)) (return nil))))
       (let ((next (%bignum-ref shifted 1)))
-	(if (oddp next)
-	    (round-up)
-	    (float-from-bits shifted len))))
+        (if (oddp next)
+            (round-up)
+            (float-from-bits shifted len))))
      ;; Otherwise, round up.
      (t
       (round-up))))))
 
 ;;;; integer length and logbitp/logcount
 
-(defun bignum-integer-length (bignum)
+(defun bignum-buffer-integer-length (bignum len)
   (declare (type bignum-type bignum))
-  (let* ((len (%bignum-length bignum))
-	 (len-1 (1- len))
-	 (digit (%bignum-ref bignum len-1)))
+  (let* ((len-1 (1- len))
+         (digit (%bignum-ref bignum len-1)))
     (declare (type bignum-index len len-1)
-	     (type bignum-element-type digit))
+             (type bignum-element-type digit))
     (+ (integer-length (%fixnum-digit-with-correct-sign digit))
        (* len-1 digit-size))))
 
+(defun bignum-integer-length (bignum)
+  (declare (type bignum-type bignum))
+  (bignum-buffer-integer-length bignum (%bignum-length bignum)))
+
 (defun bignum-logbitp (index bignum)
   (declare (type bignum-type bignum))
   (let ((len (%bignum-length bignum)))
     (declare (type bignum-index len))
     (multiple-value-bind (word-index bit-index)
-	(floor index digit-size)
+        (floor index digit-size)
       (if (>= word-index len)
-	  (not (bignum-plus-p bignum))
-	  (not (zerop (logand (%bignum-ref bignum word-index)
-			      (ash 1 bit-index))))))))
+          (not (bignum-plus-p bignum))
+          (logbitp bit-index (%bignum-ref bignum word-index))))))
 
 (defun bignum-logcount (bignum)
   (declare (type bignum-type bignum))
-  (let* ((length (%bignum-length bignum))
-	 (plusp (%bignum-0-or-plusp bignum length))
-	 (result 0))
+  (let ((length (%bignum-length bignum))
+        (result 0))
     (declare (type bignum-index length)
-	     (fixnum result))
+             (fixnum result))
     (do ((index 0 (1+ index)))
-	((= index length) result)
+        ((= index length)
+         (if (%bignum-0-or-plusp bignum length)
+             result
+             (- (* length digit-size) result)))
       (let ((digit (%bignum-ref bignum index)))
-	(declare (type bignum-element-type digit))
-	(incf result (logcount (if plusp digit (%lognot digit))))))))
+        (declare (type bignum-element-type digit))
+        (incf result (logcount digit))))))
 
 ;;;; logical operations
 
@@ -1052,7 +1326,7 @@
 (defun bignum-logical-not (a)
   (declare (type bignum-type a))
   (let* ((len (%bignum-length a))
-	 (res (%allocate-bignum len)))
+         (res (%allocate-bignum len)))
     (declare (type bignum-index len))
     (dotimes (i len res)
       (declare (type bignum-index i))
@@ -1063,19 +1337,19 @@
 (defun bignum-logical-and (a b)
   (declare (type bignum-type a b))
   (let* ((len-a (%bignum-length a))
-	 (len-b (%bignum-length b))
-	 (a-plusp (%bignum-0-or-plusp a len-a))
-	 (b-plusp (%bignum-0-or-plusp b len-b)))
+         (len-b (%bignum-length b))
+         (a-plusp (%bignum-0-or-plusp a len-a))
+         (b-plusp (%bignum-0-or-plusp b len-b)))
     (declare (type bignum-index len-a len-b))
     (cond
      ((< len-a len-b)
       (if a-plusp
-	  (logand-shorter-positive a len-a b (%allocate-bignum len-a))
-	  (logand-shorter-negative a len-a b len-b (%allocate-bignum len-b))))
+          (logand-shorter-positive a len-a b (%allocate-bignum len-a))
+          (logand-shorter-negative a len-a b len-b (%allocate-bignum len-b))))
      ((< len-b len-a)
       (if b-plusp
-	  (logand-shorter-positive b len-b a (%allocate-bignum len-b))
-	  (logand-shorter-negative b len-b a len-a (%allocate-bignum len-a))))
+          (logand-shorter-positive b len-b a (%allocate-bignum len-b))
+          (logand-shorter-negative b len-b a len-a (%allocate-bignum len-a))))
      (t (logand-shorter-positive a len-a b (%allocate-bignum len-a))))))
 
 ;;; This takes a shorter bignum, a and len-a, that is positive. Because this
@@ -1083,11 +1357,11 @@
 ;;; sign bits will mask the other bits out of b. The result is len-a big.
 (defun logand-shorter-positive (a len-a b res)
   (declare (type bignum-type a b res)
-	   (type bignum-index len-a))
+           (type bignum-index len-a))
   (dotimes (i len-a)
     (declare (type bignum-index i))
     (setf (%bignum-ref res i)
-	  (%logand (%bignum-ref a i) (%bignum-ref b i))))
+          (%logand (%bignum-ref a i) (%bignum-ref b i))))
   (%normalize-bignum res len-a))
 
 ;;; This takes a shorter bignum, a and len-a, that is negative. Because this
@@ -1095,11 +1369,11 @@
 ;;; bits will include any bits from b. The result is len-b big.
 (defun logand-shorter-negative (a len-a b len-b res)
   (declare (type bignum-type a b res)
-	   (type bignum-index len-a len-b))
+           (type bignum-index len-a len-b))
   (dotimes (i len-a)
     (declare (type bignum-index i))
     (setf (%bignum-ref res i)
-	  (%logand (%bignum-ref a i) (%bignum-ref b i))))
+          (%logand (%bignum-ref a i) (%bignum-ref b i))))
   (do ((i len-a (1+ i)))
       ((= i len-b))
     (declare (type bignum-index i))
@@ -1111,19 +1385,19 @@
 (defun bignum-logical-ior (a b)
   (declare (type bignum-type a b))
   (let* ((len-a (%bignum-length a))
-	 (len-b (%bignum-length b))
-	 (a-plusp (%bignum-0-or-plusp a len-a))
-	 (b-plusp (%bignum-0-or-plusp b len-b)))
+         (len-b (%bignum-length b))
+         (a-plusp (%bignum-0-or-plusp a len-a))
+         (b-plusp (%bignum-0-or-plusp b len-b)))
     (declare (type bignum-index len-a len-b))
     (cond
      ((< len-a len-b)
       (if a-plusp
-	  (logior-shorter-positive a len-a b len-b (%allocate-bignum len-b))
-	  (logior-shorter-negative a len-a b len-b (%allocate-bignum len-b))))
+          (logior-shorter-positive a len-a b len-b (%allocate-bignum len-b))
+          (logior-shorter-negative a len-a b len-b (%allocate-bignum len-b))))
      ((< len-b len-a)
       (if b-plusp
-	  (logior-shorter-positive b len-b a len-a (%allocate-bignum len-a))
-	  (logior-shorter-negative b len-b a len-a (%allocate-bignum len-a))))
+          (logior-shorter-positive b len-b a len-a (%allocate-bignum len-a))
+          (logior-shorter-negative b len-b a len-a (%allocate-bignum len-a))))
      (t (logior-shorter-positive a len-a b len-b (%allocate-bignum len-a))))))
 
 ;;; This takes a shorter bignum, a and len-a, that is positive. Because this
@@ -1132,11 +1406,11 @@
 ;;; is len-b long.
 (defun logior-shorter-positive (a len-a b len-b res)
   (declare (type bignum-type a b res)
-	   (type bignum-index len-a len-b))
+           (type bignum-index len-a len-b))
   (dotimes (i len-a)
     (declare (type bignum-index i))
     (setf (%bignum-ref res i)
-	  (%logior (%bignum-ref a i) (%bignum-ref b i))))
+          (%logior (%bignum-ref a i) (%bignum-ref b i))))
   (do ((i len-a (1+ i)))
       ((= i len-b))
     (declare (type bignum-index i))
@@ -1148,11 +1422,11 @@
 ;;; bits will include any bits from b. The result is len-b long.
 (defun logior-shorter-negative (a len-a b len-b res)
   (declare (type bignum-type a b res)
-	   (type bignum-index len-a len-b))
+           (type bignum-index len-a len-b))
   (dotimes (i len-a)
     (declare (type bignum-index i))
     (setf (%bignum-ref res i)
-	  (%logior (%bignum-ref a i) (%bignum-ref b i))))
+          (%logior (%bignum-ref a i) (%bignum-ref b i))))
   (do ((i len-a (1+ i))
        (sign (%sign-digit a len-a)))
       ((= i len-b))
@@ -1165,21 +1439,21 @@
 (defun bignum-logical-xor (a b)
   (declare (type bignum-type a b))
   (let ((len-a (%bignum-length a))
-	(len-b (%bignum-length b)))
+        (len-b (%bignum-length b)))
     (declare (type bignum-index len-a len-b))
     (if (< len-a len-b)
-	(bignum-logical-xor-aux a len-a b len-b (%allocate-bignum len-b))
-	(bignum-logical-xor-aux b len-b a len-a (%allocate-bignum len-a)))))
+        (bignum-logical-xor-aux a len-a b len-b (%allocate-bignum len-b))
+        (bignum-logical-xor-aux b len-b a len-a (%allocate-bignum len-a)))))
 
 ;;; This takes the shorter of two bignums in a and len-a. Res is len-b
 ;;; long. Do the XOR.
 (defun bignum-logical-xor-aux (a len-a b len-b res)
   (declare (type bignum-type a b res)
-	   (type bignum-index len-a len-b))
+           (type bignum-index len-a len-b))
   (dotimes (i len-a)
     (declare (type bignum-index i))
     (setf (%bignum-ref res i)
-	  (%logxor (%bignum-ref a i) (%bignum-ref b i))))
+          (%logxor (%bignum-ref a i) (%bignum-ref b i))))
   (do ((i len-a (1+ i))
        (sign (%sign-digit a len-a)))
       ((= i len-b))
@@ -1187,463 +1461,9 @@
     (setf (%bignum-ref res i) (%logxor sign (%bignum-ref b i))))
   (%normalize-bignum res len-b))
 
-;;;; LDB (load byte)
-
-#|
-FOR NOW WE DON'T USE LDB OR DPB. WE USE SHIFTS AND MASKS IN NUMBERS.LISP WHICH
-IS LESS EFFICIENT BUT EASIER TO MAINTAIN. BILL SAYS THIS CODE CERTAINLY WORKS!
-
-(defconstant maximum-fixnum-bits #!+ibm-rt-pc 27 #!-ibm-rt-pc 30)
-
-(defun bignum-load-byte (byte bignum)
-  (declare (type bignum-type bignum))
-  (let ((byte-len (byte-size byte))
-	(byte-pos (byte-position byte)))
-    (if (< byte-len maximum-fixnum-bits)
-	(bignum-ldb-fixnum-res bignum byte-len byte-pos)
-	(bignum-ldb-bignum-res bignum byte-len byte-pos))))
-
-;;; This returns a fixnum result of loading a byte from a bignum. In order, we
-;;; check for the following conditions:
-;;;    Insufficient bignum digits to start loading a byte --
-;;;       Return 0 or byte-len 1's depending on sign of bignum.
-;;;    One bignum digit containing the whole byte spec --
-;;;       Grab 'em, shift 'em, and mask out what we don't want.
-;;;    Insufficient bignum digits to cover crossing a digit boundary --
-;;;       Grab the available bits in the last digit, and or in whatever
-;;;       virtual sign bits we need to return a full byte spec.
-;;;    Else (we cross a digit boundary with all bits available) --
-;;;       Make a couple masks, grab what we want, shift it around, and
-;;;       LOGIOR it all together.
-;;; Because (< maximum-fixnum-bits digit-size) and
-;;;	 (< byte-len maximum-fixnum-bits),
-;;; we only cross one digit boundary if any.
-(defun bignum-ldb-fixnum-res (bignum byte-len byte-pos)
-  (multiple-value-bind (skipped-digits pos) (truncate byte-pos digit-size)
-    (let ((bignum-len (%bignum-length bignum))
-	  (s-digits+1 (1+ skipped-digits)))
-      (declare (type bignum-index bignum-len s-digits+1))
-      (if (>= skipped-digits bignum-len)
-	  (if (%bignum-0-or-plusp bignum bignum-len)
-	      0
-	      (%make-ones byte-len))
-	  (let ((end (+ pos byte-len)))
-	    (cond ((<= end digit-size)
-		   (logand (ash (%bignum-ref bignum skipped-digits) (- pos))
-			   ;; Must LOGAND after shift here.
-			   (%make-ones byte-len)))
-		  ((>= s-digits+1 bignum-len)
-		   (let* ((available-bits (- digit-size pos))
-			  (res (logand (ash (%bignum-ref bignum skipped-digits)
-					    (- pos))
-				       ;; LOGAND should be unnecessary here
-				       ;; with a logical right shift or a
-				       ;; correct unsigned-byte-32 one.
-				       (%make-ones available-bits))))
-		     (if (%bignum-0-or-plusp bignum bignum-len)
-			 res
-			 (logior (%ashl (%make-ones (- end digit-size))
-					available-bits)
-				 res))))
-		  (t
-		   (let* ((high-bits-in-first-digit (- digit-size pos))
-			  (high-mask (%make-ones high-bits-in-first-digit))
-			  (low-bits-in-next-digit (- end digit-size))
-			  (low-mask (%make-ones low-bits-in-next-digit)))
-		     (declare (type bignum-element-type high-mask low-mask))
-		     (logior (%ashl (logand (%bignum-ref bignum s-digits+1)
-					    low-mask)
-				    high-bits-in-first-digit)
-			     (logand (ash (%bignum-ref bignum skipped-digits)
-					  (- pos))
-				     ;; LOGAND should be unnecessary here with
-				     ;; a logical right shift or a correct
-				     ;; unsigned-byte-32 one.
-				     high-mask))))))))))
-
-;;; This returns a bignum result of loading a byte from a bignum. In order, we
-;;; check for the following conditions:
-;;;    Insufficient bignum digits to start loading a byte --
-;;;    Byte-pos starting on a digit boundary --
-;;;    Byte spec contained in one bignum digit --
-;;;       Grab the bits we want and stick them in a single digit result.
-;;;       Since we know byte-pos is non-zero here, we know our single digit
-;;;       will have a zero high sign bit.
-;;;    Else (unaligned multiple digits) --
-;;;       This is like doing a shift right combined with either masking
-;;;       out unwanted high bits from bignum or filling in virtual sign
-;;;       bits if bignum had insufficient bits. We use SHIFT-RIGHT-ALIGNED
-;;;       and reference lots of local variables this macro establishes.
-(defun bignum-ldb-bignum-res (bignum byte-len byte-pos)
-  (multiple-value-bind (skipped-digits pos) (truncate byte-pos digit-size)
-    (let ((bignum-len (%bignum-length bignum)))
-      (declare (type bignum-index bignum-len))
-      (cond
-       ((>= skipped-digits bignum-len)
-	(make-bignum-virtual-ldb-bits bignum bignum-len byte-len))
-       ((zerop pos)
-	(make-aligned-ldb-bignum bignum bignum-len byte-len skipped-digits))
-       ((< (+ pos byte-len) digit-size)
-	(let ((res (%allocate-bignum 1)))
-	  (setf (%bignum-ref res 0)
-		(logand (%ashr (%bignum-ref bignum skipped-digits) pos)
-			(%make-ones byte-len)))
-	  res))
-       (t
-	(make-unaligned-ldb-bignum bignum bignum-len
-				   byte-len skipped-digits pos))))))
-
-;;; This returns bits from bignum that don't physically exist. These are
-;;; all zero or one depending on the sign of the bignum.
-(defun make-bignum-virtual-ldb-bits (bignum bignum-len byte-len)
-  (if (%bignum-0-or-plusp bignum bignum-len)
-      0
-      (multiple-value-bind (res-len-1 extra) (truncate byte-len digit-size)
-	(declare (type bignum-index res-len-1))
-	(let* ((res-len (1+ res-len-1))
-	       (res (%allocate-bignum res-len)))
-	  (declare (type bignum-index res-len))
-	  (do ((j 0 (1+ j)))
-	      ((= j res-len-1)
-	       (setf (%bignum-ref res j) (%make-ones extra))
-	       (%normalize-bignum res res-len))
-	    (declare (type bignum-index j))
-	    (setf (%bignum-ref res j) all-ones-digit))))))
-
-;;; Since we are picking up aligned digits, we just copy the whole digits
-;;; we want and fill in extra bits. We might have a byte-len that extends
-;;; off the end of the bignum, so we may have to fill in extra 1's if the
-;;; bignum is negative.
-(defun make-aligned-ldb-bignum (bignum bignum-len byte-len skipped-digits)
-  (multiple-value-bind (res-len-1 extra) (truncate byte-len digit-size)
-    (declare (type bignum-index res-len-1))
-    (let* ((res-len (1+ res-len-1))
-	   (res (%allocate-bignum res-len)))
-      (declare (type bignum-index res-len))
-      (do ((i skipped-digits (1+ i))
-	   (j 0 (1+ j)))
-	  ((or (= j res-len-1) (= i bignum-len))
-	   (cond ((< i bignum-len)
-		  (setf (%bignum-ref res j)
-			(logand (%bignum-ref bignum i)
-				(the bignum-element-type (%make-ones extra)))))
-		 ((%bignum-0-or-plusp bignum bignum-len))
-		 (t
-		  (do ((j j (1+ j)))
-		      ((= j res-len-1)
-		       (setf (%bignum-ref res j) (%make-ones extra)))
-		    (setf (%bignum-ref res j) all-ones-digit))))
-	   (%normalize-bignum res res-len))
-      (declare (type bignum-index i j))
-      (setf (%bignum-ref res j) (%bignum-ref bignum i))))))
-
-;;; This grabs unaligned bignum bits from bignum assuming byte-len causes at
-;;; least one digit boundary crossing. We use SHIFT-RIGHT-UNALIGNED referencing
-;;; lots of local variables established by it.
-(defun make-unaligned-ldb-bignum (bignum
-				  bignum-len
-				  byte-len
-				  skipped-digits
-				  pos)
-  (multiple-value-bind (res-len-1 extra) (truncate byte-len digit-size)
-    (shift-right-unaligned
-     bignum skipped-digits pos (1+ res-len-1)
-     ((or (= j res-len-1) (= i+1 bignum-len))
-      (cond ((= j res-len-1)
-	     (cond
-	      ((< extra high-bits-in-first-digit)
-	       (setf (%bignum-ref res j)
-		     (logand (ash (%bignum-ref bignum i) minus-start-pos)
-			     ;; Must LOGAND after shift here.
-			     (%make-ones extra))))
-	      (t
-	       (setf (%bignum-ref res j)
-		     (logand (ash (%bignum-ref bignum i) minus-start-pos)
-			     ;; LOGAND should be unnecessary here with a logical
-			     ;; right shift or a correct unsigned-byte-32 one.
-			     high-mask))
-	       (when (%bignum-0-or-plusp bignum bignum-len)
-		 (setf (%bignum-ref res j)
-		       (logior (%bignum-ref res j)
-			       (%ashl (%make-ones
-				       (- extra high-bits-in-first-digit))
-				      high-bits-in-first-digit)))))))
-	    (t
-	     (setf (%bignum-ref res j)
-		   (logand (ash (%bignum-ref bignum i) minus-start-pos)
-			   ;; LOGAND should be unnecessary here with a logical
-			   ;; right shift or a correct unsigned-byte-32 one.
-			   high-mask))
-	     (unless (%bignum-0-or-plusp bignum bignum-len)
-	       ;; Fill in upper half of this result digit with 1's.
-	       (setf (%bignum-ref res j)
-		     (logior (%bignum-ref res j)
-			     (%ashl low-mask high-bits-in-first-digit)))
-	       ;; Fill in any extra 1's we need to be byte-len long.
-	       (do ((j (1+ j) (1+ j)))
-		   ((>= j res-len-1)
-		    (setf (%bignum-ref res j) (%make-ones extra)))
-		 (setf (%bignum-ref res j) all-ones-digit)))))
-      (%normalize-bignum res res-len))
-     res)))
-
-;;;; DPB (deposit byte)
-
-(defun bignum-deposit-byte (new-byte byte-spec bignum)
-  (declare (type bignum-type bignum))
-  (let* ((byte-len (byte-size byte-spec))
-	 (byte-pos (byte-position byte-spec))
-	 (bignum-len (%bignum-length bignum))
-	 (bignum-plusp (%bignum-0-or-plusp bignum bignum-len))
-	 (byte-end (+ byte-pos byte-len))
-	 (res-len (1+ (max (ceiling byte-end digit-size) bignum-len)))
-	 (res (%allocate-bignum res-len)))
-    (declare (type bignum-index bignum-len res-len))
-    ;; Fill in an extra sign digit in case we set what would otherwise be the
-    ;; last digit's last bit. Normalize at the end in case this was
-    ;; unnecessary.
-    (unless bignum-plusp
-      (setf (%bignum-ref res (1- res-len)) all-ones-digit))
-    (multiple-value-bind (end-digit end-bits) (truncate byte-end digit-size)
-      (declare (type bignum-index end-digit))
-      ;; Fill in bits from bignum up to byte-pos.
-      (multiple-value-bind (pos-digit pos-bits) (truncate byte-pos digit-size)
-	(declare (type bignum-index pos-digit))
-	(do ((i 0 (1+ i))
-	     (end (min pos-digit bignum-len)))
-	    ((= i end)
-	     (cond ((< i bignum-len)
-		    (unless (zerop pos-bits)
-		      (setf (%bignum-ref res i)
-			    (logand (%bignum-ref bignum i)
-				    (%make-ones pos-bits)))))
-		   (bignum-plusp)
-		   (t
-		    (do ((i i (1+ i)))
-			((= i pos-digit)
-			 (unless (zerop pos-bits)
-			   (setf (%bignum-ref res i) (%make-ones pos-bits))))
-		      (setf (%bignum-ref res i) all-ones-digit)))))
-	  (setf (%bignum-ref res i) (%bignum-ref bignum i)))
-	;; Fill in bits from new-byte.
-	(if (typep new-byte 'fixnum)
-	    (deposit-fixnum-bits new-byte byte-len pos-digit pos-bits
-				 end-digit end-bits res)
-	    (deposit-bignum-bits new-byte byte-len pos-digit pos-bits
-				 end-digit end-bits res)))
-      ;; Fill in remaining bits from bignum after byte-spec.
-      (when (< end-digit bignum-len)
-	(setf (%bignum-ref res end-digit)
-	      (logior (logand (%bignum-ref bignum end-digit)
-			      (%ashl (%make-ones (- digit-size end-bits))
-				     end-bits))
-		      ;; DEPOSIT-FIXNUM-BITS and DEPOSIT-BIGNUM-BITS only store
-		      ;; bits from new-byte into res's end-digit element, so
-		      ;; we don't need to mask out unwanted high bits.
-		      (%bignum-ref res end-digit)))
-	(do ((i (1+ end-digit) (1+ i)))
-	    ((= i bignum-len))
-	  (setf (%bignum-ref res i) (%bignum-ref bignum i)))))
-    (%normalize-bignum res res-len)))
-
-;;; This starts at result's pos-digit skipping pos-bits, and it stores bits
-;;; from new-byte, a fixnum, into result. It effectively stores byte-len
-;;; number of bits, but never stores past end-digit and end-bits in result.
-;;; The first branch fires when all the bits we want from new-byte are present;
-;;; if byte-len crosses from the current result digit into the next, the last
-;;; argument to DEPOSIT-FIXNUM-DIGIT is a mask for those bits. The second
-;;; branch handles the need to grab more bits than the fixnum new-byte has, but
-;;; new-byte is positive; therefore, any virtual bits are zero. The mask for
-;;; bits that don't fit in the current result digit is simply the remaining
-;;; bits in the bignum digit containing new-byte; we don't care if we store
-;;; some extra in the next result digit since they will be zeros. The last
-;;; branch handles the need to grab more bits than the fixnum new-byte has, but
-;;; new-byte is negative; therefore, any virtual bits must be explicitly filled
-;;; in as ones. We call DEPOSIT-FIXNUM-DIGIT to grab what bits actually exist
-;;; and to fill in the current result digit.
-(defun deposit-fixnum-bits (new-byte byte-len pos-digit pos-bits
-			    end-digit end-bits result)
-  (declare (type bignum-index pos-digit end-digit))
-  (let ((other-bits (- digit-size pos-bits))
-	(new-byte-digit (%fixnum-to-digit new-byte)))
-    (declare (type bignum-element-type new-byte-digit))
-    (cond ((< byte-len maximum-fixnum-bits)
-	   (deposit-fixnum-digit new-byte-digit byte-len pos-digit pos-bits
-				 other-bits result
-				 (- byte-len other-bits)))
-	  ((or (plusp new-byte) (zerop new-byte))
-	   (deposit-fixnum-digit new-byte-digit byte-len pos-digit pos-bits
-				 other-bits result pos-bits))
-	  (t
-	   (multiple-value-bind (digit bits)
-	       (deposit-fixnum-digit new-byte-digit byte-len pos-digit pos-bits
-				     other-bits result
-				     (if (< (- byte-len other-bits) digit-size)
-					 (- byte-len other-bits)
-					 digit-size))
-	     (declare (type bignum-index digit))
-	     (cond ((< digit end-digit)
-		    (setf (%bignum-ref result digit)
-			  (logior (%bignum-ref result digit)
-				  (%ashl (%make-ones (- digit-size bits)) bits)))
-		    (do ((i (1+ digit) (1+ i)))
-			((= i end-digit)
-			 (setf (%bignum-ref result i) (%make-ones end-bits)))
-		      (setf (%bignum-ref result i) all-ones-digit)))
-		   ((> digit end-digit))
-		   ((< bits end-bits)
-		    (setf (%bignum-ref result digit)
-			  (logior (%bignum-ref result digit)
-				  (%ashl (%make-ones (- end-bits bits))
-					 bits))))))))))
-
-;;; This fills in the current result digit from new-byte-digit. The first case
-;;; handles everything we want fitting in the current digit, and other-bits is
-;;; the number of bits remaining to be filled in result's current digit. This
-;;; number is digit-size minus pos-bits. The second branch handles filling in
-;;; result's current digit, and it shoves the unused bits of new-byte-digit
-;;; into the next result digit. This is correct regardless of new-byte-digit's
-;;; sign. It returns the new current result digit and how many bits already
-;;; filled in the result digit.
-(defun deposit-fixnum-digit (new-byte-digit byte-len pos-digit pos-bits
-			     other-bits result next-digit-bits-needed)
-  (declare (type bignum-index pos-digit)
-	   (type bignum-element-type new-byte-digit next-digit-mask))
-  (cond ((<= byte-len other-bits)
-	 ;; Bits from new-byte fit in the current result digit.
-	 (setf (%bignum-ref result pos-digit)
-	       (logior (%bignum-ref result pos-digit)
-		       (%ashl (logand new-byte-digit (%make-ones byte-len))
-			      pos-bits)))
-	 (if (= byte-len other-bits)
-	     (values (1+ pos-digit) 0)
-	     (values pos-digit (+ byte-len pos-bits))))
-	(t
-	 ;; Some of new-byte's bits go in current result digit.
-	 (setf (%bignum-ref result pos-digit)
-	       (logior (%bignum-ref result pos-digit)
-		       (%ashl (logand new-byte-digit (%make-ones other-bits))
-			      pos-bits)))
-	 (let ((pos-digit+1 (1+ pos-digit)))
-	   ;; The rest of new-byte's bits go in the next result digit.
-	   (setf (%bignum-ref result pos-digit+1)
-		 (logand (ash new-byte-digit (- other-bits))
-			 ;; Must LOGAND after shift here.
-			 (%make-ones next-digit-bits-needed)))
-	   (if (= next-digit-bits-needed digit-size)
-	       (values (1+ pos-digit+1) 0)
-	       (values pos-digit+1 next-digit-bits-needed))))))
-
-;;; This starts at result's pos-digit skipping pos-bits, and it stores bits
-;;; from new-byte, a bignum, into result. It effectively stores byte-len
-;;; number of bits, but never stores past end-digit and end-bits in result.
-;;; When handling a starting bit unaligned with a digit boundary, we check
-;;; in the second branch for the byte spec fitting into the pos-digit element
-;;; after after pos-bits; DEPOSIT-UNALIGNED-BIGNUM-BITS expects at least one
-;;; digit boundary crossing.
-(defun deposit-bignum-bits (bignum-byte byte-len pos-digit pos-bits
-			    end-digit end-bits result)
-  (declare (type bignum-index pos-digit end-digit))
-  (cond ((zerop pos-bits)
-	 (deposit-aligned-bignum-bits bignum-byte pos-digit end-digit end-bits
-				      result))
-	((or (= end-digit pos-digit)
-	     (and (= end-digit (1+ pos-digit))
-		  (zerop end-bits)))
-	 (setf (%bignum-ref result pos-digit)
-	       (logior (%bignum-ref result pos-digit)
-		       (%ashl (logand (%bignum-ref bignum-byte 0)
-				      (%make-ones byte-len))
-			      pos-bits))))
-	(t (deposit-unaligned-bignum-bits bignum-byte pos-digit pos-bits
-					  end-digit end-bits result))))
-
-;;; This deposits bits from bignum-byte into result starting at pos-digit and
-;;; the zero'th bit. It effectively only stores bits to end-bits in the
-;;; end-digit element of result. The loop termination code takes care of
-;;; picking up the last digit's bits or filling in virtual negative sign bits.
-(defun deposit-aligned-bignum-bits (bignum-byte pos-digit end-digit end-bits
-				    result)
-  (declare (type bignum-index pos-digit end-digit))
-  (let* ((bignum-len (%bignum-length bignum-byte))
-	 (bignum-plusp (%bignum-0-or-plusp bignum-byte bignum-len)))
-    (declare (type bignum-index bignum-len))
-    (do ((i 0 (1+ i ))
-	 (j pos-digit (1+ j)))
-	((or (= j end-digit) (= i bignum-len))
-	 (cond ((= j end-digit)
-		(cond ((< i bignum-len)
-		       (setf (%bignum-ref result j)
-			     (logand (%bignum-ref bignum-byte i)
-				     (%make-ones end-bits))))
-		      (bignum-plusp)
-		      (t
-		       (setf (%bignum-ref result j) (%make-ones end-bits)))))
-	       (bignum-plusp)
-	       (t
-		(do ((j j (1+ j)))
-		    ((= j end-digit)
-		     (setf (%bignum-ref result j) (%make-ones end-bits)))
-		  (setf (%bignum-ref result j) all-ones-digit)))))
-      (setf (%bignum-ref result j) (%bignum-ref bignum-byte i)))))
-
-;;; This assumes at least one digit crossing.
-(defun deposit-unaligned-bignum-bits (bignum-byte pos-digit pos-bits
-				      end-digit end-bits result)
-  (declare (type bignum-index pos-digit end-digit))
-  (let* ((bignum-len (%bignum-length bignum-byte))
-	 (bignum-plusp (%bignum-0-or-plusp bignum-byte bignum-len))
-	 (low-mask (%make-ones pos-bits))
-	 (bits-past-pos-bits (- digit-size pos-bits))
-	 (high-mask (%make-ones bits-past-pos-bits))
-	 (minus-high-bits (- bits-past-pos-bits)))
-    (declare (type bignum-element-type low-mask high-mask)
-	     (type bignum-index bignum-len))
-    (do ((i 0 (1+ i))
-	 (j pos-digit j+1)
-	 (j+1 (1+ pos-digit) (1+ j+1)))
-	((or (= j end-digit) (= i bignum-len))
-	 (cond
-	  ((= j end-digit)
-	   (setf (%bignum-ref result j)
-		 (cond
-		  ((>= pos-bits end-bits)
-		   (logand (%bignum-ref result j) (%make-ones end-bits)))
-		  ((< i bignum-len)
-		   (logior (%bignum-ref result j)
-			   (%ashl (logand (%bignum-ref bignum-byte i)
-					  (%make-ones (- end-bits pos-bits)))
-				  pos-bits)))
-		  (bignum-plusp
-		   (logand (%bignum-ref result j)
-			   ;; 0's between pos-bits and end-bits positions.
-			   (logior (%ashl (%make-ones (- digit-size end-bits))
-					  end-bits)
-				   low-mask)))
-		  (t (logior (%bignum-ref result j)
-			     (%ashl (%make-ones (- end-bits pos-bits))
-				    pos-bits))))))
-	  (bignum-plusp)
-	  (t
-	   (setf (%bignum-ref result j)
-		 (%ashl (%make-ones bits-past-pos-bits) pos-bits))
-	   (do ((j j+1 (1+ j)))
-	       ((= j end-digit)
-		(setf (%bignum-ref result j) (%make-ones end-bits)))
-	     (declare (type bignum-index j))
-	     (setf (%bignum-ref result j) all-ones-digit)))))
-      (declare (type bignum-index i j j+1))
-      (let ((digit (%bignum-ref bignum-byte i)))
-	(declare (type bignum-element-type digit))
-	(setf (%bignum-ref result j)
-	      (logior (%bignum-ref result j)
-		      (%ashl (logand digit high-mask) pos-bits)))
-	(setf (%bignum-ref result j+1)
-	      (logand (ash digit minus-high-bits)
-		      ;; LOGAND should be unnecessary here with a logical right
-		      ;; shift or a correct unsigned-byte-32 one.
-		      low-mask))))))
-|#
+;;;; There used to be a bunch of code to implement "efficient" versions of LDB
+;;;; and DPB here.  But it apparently was never used, so it's been deleted.
+;;;;   --njf, 2007-02-04
 
 ;;;; TRUNCATE
 
@@ -1677,15 +1497,15 @@ IS LESS EFFICIENT BUT EASIER TO MAINTAIN. BILL SAYS THIS CODE CERTAINLY WORKS!
 ;;; j = last digit of y.
 ;;;
 ;;; compute guess.
-;;; if x[i] = y[j] then g = #xFFFFFFFF
+;;; if x[i] = y[j] then g = (1- (ash 1 digit-size))
 ;;; else g = x[i]x[i-1]/y[j].
 ;;;
 ;;; check guess.
 ;;; %UNSIGNED-MULTIPLY returns b and c defined below.
 ;;;    a = x[i-1] - (logand (* g y[j]) #xFFFFFFFF).
 ;;;       Use %UNSIGNED-MULTIPLY taking low-order result.
-;;;    b = (logand (ash (* g y[j-1]) -32) #xFFFFFFFF).
-;;;    c = (logand (* g y[j-1]) #xFFFFFFFF).
+;;;    b = (logand (ash (* g y[j-1]) (- digit-size)) (1- (ash 1 digit-size))).
+;;;    c = (logand (* g y[j-1]) (1- (ash 1 digit-size))).
 ;;; if a < b, okay.
 ;;; if a > b, guess is too high
 ;;;    g = g - 1; go back to "check guess".
@@ -1717,517 +1537,336 @@ IS LESS EFFICIENT BUT EASIER TO MAINTAIN. BILL SAYS THIS CODE CERTAINLY WORKS!
 ;;;
 ;;; Normalize quotient and remainder. Cons result if necessary.
 
-;;; These are used by BIGNUM-TRUNCATE and friends in the general case.
-(defvar *truncate-x*)
-(defvar *truncate-y*)
-
-;;; Divide X by Y returning the quotient and remainder. In the
-;;; general case, we shift Y to set up for the algorithm, and we use
-;;; two buffers to save consing intermediate values. X gets
-;;; destructively modified to become the remainder, and we have to
-;;; shift it to account for the initial Y shift. After we multiple
-;;; bind q and r, we first fix up the signs and then return the
-;;; normalized results.
+
+;;; This used to be split into multiple functions, which shared state
+;;; in special variables *TRUNCATE-X* and *TRUNCATE-Y*. Having so many
+;;; special variable accesses in tight inner loops was having a large
+;;; effect on performance, so the helper functions have now been
+;;; refactored into local functions and the special variables into
+;;; lexicals.  There was also a lot of boxing and unboxing of
+;;; (UNSIGNED-BYTE 32)'s going on, which this refactoring
+;;; eliminated. This improves the performance on some CL-BENCH tests
+;;; by up to 50%, which is probably signigicant enough to justify the
+;;; reduction in readability that was introduced. --JES, 2004-08-07
 (defun bignum-truncate (x y)
   (declare (type bignum-type x y))
-  (let* ((x-plusp (%bignum-0-or-plusp x (%bignum-length x)))
-	 (y-plusp (%bignum-0-or-plusp y (%bignum-length y)))
-	 (x (if x-plusp x (negate-bignum x nil)))
-	 (y (if y-plusp y (negate-bignum y nil)))
-	 (len-x (%bignum-length x))
-	 (len-y (%bignum-length y)))
-    (multiple-value-bind (q r)
-	(cond ((< len-y 2)
-	       (bignum-truncate-single-digit x len-x y))
-	      ((plusp (bignum-compare y x))
-	       (let ((res (%allocate-bignum len-x)))
-		 (dotimes (i len-x)
-		   (setf (%bignum-ref res i) (%bignum-ref x i)))
-		 (values 0 res)))
-	      (t
-	       (let ((len-x+1 (1+ len-x)))
-		 (with-bignum-buffers ((*truncate-x* len-x+1)
-				       (*truncate-y* (1+ len-y)))
-		   (let ((y-shift (shift-y-for-truncate y)))
-		     (shift-and-store-truncate-buffers x len-x y len-y y-shift)
-		     (values (return-quotient-leaving-remainder len-x+1 len-y)
-			     ;; Now that RETURN-QUOTIENT-LEAVING-REMAINDER
-			     ;; has executed, we just tidy up the remainder
-			     ;; (in *TRUNCATE-X*) and return it.
-			     (cond
-			      ((zerop y-shift)
-			       (let ((res (%allocate-bignum len-y)))
-				 (declare (type bignum-type res))
-				 (bignum-replace res *truncate-x* :end2 len-y)
-				 (%normalize-bignum res len-y)))
-			      (t
-			       (shift-right-unaligned
-				*truncate-x* 0 y-shift len-y
-				((= j res-len-1)
-				 (setf (%bignum-ref res j)
-				       (%ashr (%bignum-ref *truncate-x* i)
-					      y-shift))
-				 (%normalize-bignum res res-len))
-				res)))))))))
-      (let ((quotient (cond ((eq x-plusp y-plusp) q)
-			    ((typep q 'fixnum) (the fixnum (- q)))
-			    (t (negate-bignum-in-place q))))
-	    (rem (cond (x-plusp r)
-		       ((typep r 'fixnum) (the fixnum (- r)))
-		       (t (negate-bignum-in-place r)))))
-	(values (if (typep quotient 'fixnum)
-		    quotient
-		    (%normalize-bignum quotient (%bignum-length quotient)))
-		(if (typep rem 'fixnum)
-		    rem
-		    (%normalize-bignum rem (%bignum-length rem))))))))
-
-;;; Divide X by Y when Y is a single bignum digit. BIGNUM-TRUNCATE
-;;; fixes up the quotient and remainder with respect to sign and
-;;; normalization.
-;;;
-;;; We don't have to worry about shifting Y to make its most
-;;; significant digit sufficiently large for %FLOOR to return 32-bit
-;;; quantities for the q-digit and r-digit. If Y is a single digit
-;;; bignum, it is already large enough for %FLOOR. That is, it has
-;;; some bits on pretty high in the digit.
-(defun bignum-truncate-single-digit (x len-x y)
-  (declare (type bignum-index len-x))
-  (let ((q (%allocate-bignum len-x))
-	(r 0)
-	(y (%bignum-ref y 0)))
-    (declare (type bignum-element-type r y))
-    (do ((i (1- len-x) (1- i)))
-	((minusp i))
-      (multiple-value-bind (q-digit r-digit) (%floor r (%bignum-ref x i) y)
-	(declare (type bignum-element-type q-digit r-digit))
-	(setf (%bignum-ref q i) q-digit)
-	(setf r r-digit)))
-    (let ((rem (%allocate-bignum 1)))
-      (setf (%bignum-ref rem 0) r)
-      (values q rem))))
-
-;;; a helper function for BIGNUM-TRUNCATE
-;;;
-;;; Divide *TRUNCATE-X* by *TRUNCATE-Y*, returning the quotient
-;;; and destructively modifying *TRUNCATE-X* so that it holds
-;;; the remainder.
-;;;
-;;; LEN-X and LEN-Y tell us how much of the buffers we care about.
-;;;
-;;; *TRUNCATE-X* definitely has at least three digits, and it has one
-;;; more than *TRUNCATE-Y*. This keeps i, i-1, i-2, and low-x-digit
-;;; happy. Thanks to SHIFT-AND-STORE-TRUNCATE-BUFFERS.
-(defun return-quotient-leaving-remainder (len-x len-y)
-  (declare (type bignum-index len-x len-y))
-  (let* ((len-q (- len-x len-y))
-	 ;; Add one for extra sign digit in case high bit is on.
-	 (q (%allocate-bignum (1+ len-q)))
-	 (k (1- len-q))
-	 (y1 (%bignum-ref *truncate-y* (1- len-y)))
-	 (y2 (%bignum-ref *truncate-y* (- len-y 2)))
-	 (i (1- len-x))
-	 (i-1 (1- i))
-	 (i-2 (1- i-1))
-	 (low-x-digit (- i len-y)))
-    (declare (type bignum-index len-q k i i-1 i-2 low-x-digit)
-	     (type bignum-element-type y1 y2))
-    (loop
-      (setf (%bignum-ref q k)
-	    (try-bignum-truncate-guess
-	     ;; This modifies *TRUNCATE-X*. Must access elements each pass.
-	     (bignum-truncate-guess y1 y2
-				    (%bignum-ref *truncate-x* i)
-				    (%bignum-ref *truncate-x* i-1)
-				    (%bignum-ref *truncate-x* i-2))
-	     len-y low-x-digit))
-      (cond ((zerop k) (return))
-	    (t (decf k)
-	       (decf low-x-digit)
-	       (shiftf i i-1 i-2 (1- i-2)))))
-    q))
-
-;;; This takes a digit guess, multiplies it by *TRUNCATE-Y* for a
-;;; result one greater in length than LEN-Y, and subtracts this result
-;;; from *TRUNCATE-X*. LOW-X-DIGIT is the first digit of X to start
-;;; the subtraction, and we know X is long enough to subtract a LEN-Y
-;;; plus one length bignum from it. Next we check the result of the
-;;; subtraction, and if the high digit in X became negative, then our
-;;; guess was one too big. In this case, return one less than GUESS
-;;; passed in, and add one value of Y back into X to account for
-;;; subtracting one too many. Knuth shows that the guess is wrong on
-;;; the order of 3/b, where b is the base (2 to the digit-size power)
-;;; -- pretty rarely.
-(defun try-bignum-truncate-guess (guess len-y low-x-digit)
-  (declare (type bignum-index low-x-digit len-y)
-	   (type bignum-element-type guess))
-  (let ((carry-digit 0)
-	(borrow 1)
-	(i low-x-digit))
-    (declare (type bignum-element-type carry-digit)
-	     (type bignum-index i)
-	     (fixnum borrow))
-    ;; Multiply guess and divisor, subtracting from dividend simultaneously.
-    (dotimes (j len-y)
-      (multiple-value-bind (high-digit low-digit)
-	  (%multiply-and-add guess
-			     (%bignum-ref *truncate-y* j)
-			     carry-digit)
-	(declare (type bignum-element-type high-digit low-digit))
-	(setf carry-digit high-digit)
-	(multiple-value-bind (x temp-borrow)
-	    (%subtract-with-borrow (%bignum-ref *truncate-x* i)
-				   low-digit
-				   borrow)
-	  (declare (type bignum-element-type x)
-		   (fixnum temp-borrow))
-	  (setf (%bignum-ref *truncate-x* i) x)
-	  (setf borrow temp-borrow)))
-      (incf i))
-    (setf (%bignum-ref *truncate-x* i)
-	  (%subtract-with-borrow (%bignum-ref *truncate-x* i)
-				 carry-digit borrow))
-    ;; See whether guess is off by one, adding one Y back in if necessary.
-    (cond ((%digit-0-or-plusp (%bignum-ref *truncate-x* i))
-	   guess)
-	  (t
-	   ;; If subtraction has negative result, add one divisor value back
-	   ;; in. The guess was one too large in magnitude.
-	   (let ((i low-x-digit)
-		 (carry 0))
-	     (dotimes (j len-y)
-	       (multiple-value-bind (v k)
-		   (%add-with-carry (%bignum-ref *truncate-y* j)
-				    (%bignum-ref *truncate-x* i)
-				    carry)
-		 (declare (type bignum-element-type v))
-		 (setf (%bignum-ref *truncate-x* i) v)
-		 (setf carry k))
-	       (incf i))
-	     (setf (%bignum-ref *truncate-x* i)
-		   (%add-with-carry (%bignum-ref *truncate-x* i) 0 carry)))
-	   (%subtract-with-borrow guess 1 1)))))
-
-;;; This returns a guess for the next division step. Y1 is the highest y
-;;; digit, and y2 is the second to highest y digit. The x... variables are
-;;; the three highest x digits for the next division step.
-;;;
-;;; From Knuth, our guess is either all ones or x-i and x-i-1 divided by y1,
-;;; depending on whether x-i and y1 are the same. We test this guess by
-;;; determining whether guess*y2 is greater than the three high digits of x
-;;; minus guess*y1 shifted left one digit:
-;;;    ------------------------------
-;;;   |    x-i    |   x-i-1  | x-i-2 |
-;;;    ------------------------------
-;;;    ------------------------------
-;;; - | g*y1 high | g*y1 low |   0   |
-;;;    ------------------------------
-;;;		...		  <   guess*y2     ???
-;;; If guess*y2 is greater, then we decrement our guess by one and try again.
-;;; This returns a guess that is either correct or one too large.
-(defun bignum-truncate-guess (y1 y2 x-i x-i-1 x-i-2)
-  (declare (type bignum-element-type y1 y2 x-i x-i-1 x-i-2))
-  (let ((guess (if (%digit-compare x-i y1)
-		   all-ones-digit
-		   (%floor x-i x-i-1 y1))))
-    (declare (type bignum-element-type guess))
-    (loop
-      (multiple-value-bind (high-guess*y1 low-guess*y1) (%multiply guess y1)
-	(declare (type bignum-element-type low-guess*y1 high-guess*y1))
-	(multiple-value-bind (high-guess*y2 low-guess*y2)
-	    (%multiply guess y2)
-	  (declare (type bignum-element-type high-guess*y2 low-guess*y2))
-	  (multiple-value-bind (middle-digit borrow)
-	      (%subtract-with-borrow x-i-1 low-guess*y1 1)
-	    (declare (type bignum-element-type middle-digit)
-		     (fixnum borrow))
-	    ;; Supplying borrow of 1 means there was no borrow, and we know
-	    ;; x-i-2 minus 0 requires no borrow.
-	    (let ((high-digit (%subtract-with-borrow x-i high-guess*y1 borrow)))
-	      (declare (type bignum-element-type high-digit))
-	      (if (and (%digit-compare high-digit 0)
-		       (or (%digit-greater high-guess*y2 middle-digit)
-			   (and (%digit-compare middle-digit high-guess*y2)
-				(%digit-greater low-guess*y2 x-i-2))))
-		  (setf guess (%subtract-with-borrow guess 1 1))
-		  (return guess)))))))))
-
-;;; This returns the amount to shift y to place a one in the second highest
-;;; bit. Y must be positive. If the last digit of y is zero, then y has a
-;;; one in the previous digit's sign bit, so we know it will take one less
-;;; than digit-size to get a one where we want. Otherwise, we count how many
-;;; right shifts it takes to get zero; subtracting this value from digit-size
-;;; tells us how many high zeros there are which is one more than the shift
-;;; amount sought.
-;;;
-;;; Note: This is exactly the same as one less than the integer-length of the
-;;; last digit subtracted from the digit-size.
-;;;
-;;; We shift y to make it sufficiently large that doing the 64-bit by 32-bit
-;;; %FLOOR calls ensures the quotient and remainder fit in 32-bits.
-(defun shift-y-for-truncate (y)
-  (let* ((len (%bignum-length y))
-	 (last (%bignum-ref y (1- len))))
-    (declare (type bignum-index len)
-	     (type bignum-element-type last))
-    (- digit-size (integer-length last) 1)))
-
-;;; Stores two bignums into the truncation bignum buffers, shifting them on the
-;;; way in. This assumes x and y are positive and at least two in length, and
-;;; it assumes *truncate-x* and *truncate-y* are one digit longer than x and y.
-(defun shift-and-store-truncate-buffers (x len-x y len-y shift)
-  (declare (type bignum-index len-x len-y)
-	   (type (integer 0 (#.digit-size)) shift))
-  (cond ((zerop shift)
-	 (bignum-replace *truncate-x* x :end1 len-x)
-	 (bignum-replace *truncate-y* y :end1 len-y))
-	(t
-	 (bignum-ashift-left-unaligned x 0 shift (1+ len-x) *truncate-x*)
-	 (bignum-ashift-left-unaligned y 0 shift (1+ len-y) *truncate-y*))))
+  (let (truncate-x truncate-y)
+    (labels
+        ;;; Divide X by Y when Y is a single bignum digit. BIGNUM-TRUNCATE
+        ;;; fixes up the quotient and remainder with respect to sign and
+        ;;; normalization.
+        ;;;
+        ;;; We don't have to worry about shifting Y to make its most
+        ;;; significant digit sufficiently large for %BIGFLOOR to return
+        ;;; digit-size quantities for the q-digit and r-digit. If Y is
+        ;;; a single digit bignum, it is already large enough for
+        ;;; %BIGFLOOR. That is, it has some bits on pretty high in the
+        ;;; digit.
+        ((bignum-truncate-single-digit (x len-x y)
+           (declare (type bignum-index len-x))
+           (let ((y (%bignum-ref y 0)))
+             (declare (type bignum-element-type y))
+             (if (not (logtest y (1- y)))
+                 ;; Y is a power of two.
+                 ;; SHIFT-RIGHT-UNALIGNED won't do the right thing
+                 ;; with a shift count of 0 or -1, so special case this.
+                 (cond ((= y 0)
+                        (error 'division-by-zero))
+                       ((= y 1)
+                        ;; We could probably get away with (VALUES X 0)
+                        ;; here, but it's not clear that some of the
+                        ;; normalization logic further down would avoid
+                        ;; mutilating X.  Just go ahead and cons, consing's
+                        ;; cheap.
+                        (values (copy-bignum x len-x) 0))
+                       (t
+                        (let ((n-bits (1- (integer-length y))))
+                          (values
+                           (shift-right-unaligned x 0 n-bits len-x
+                                                  ((= j res-len-1)
+                                                   (setf (%bignum-ref res j)
+                                                         (%ashr (%bignum-ref x i) n-bits))
+                                                   res)
+                                                  res)
+                           (logand (%bignum-ref x 0) (1- y))))))
+                 (do ((i (1- len-x) (1- i))
+                      (q (%allocate-bignum len-x))
+                      (r 0))
+                     ((minusp i)
+                      (let ((rem (%allocate-bignum 1)))
+                        (setf (%bignum-ref rem 0) r)
+                        (values q rem)))
+                   (declare (type bignum-element-type r))
+                   (multiple-value-bind (q-digit r-digit)
+                       (%bigfloor r (%bignum-ref x i) y)
+                     (declare (type bignum-element-type q-digit r-digit))
+                     (setf (%bignum-ref q i) q-digit)
+                     (setf r r-digit))))))
+        ;;; This returns a guess for the next division step. Y1 is the
+        ;;; highest y digit, and y2 is the second to highest y
+        ;;; digit. The x... variables are the three highest x digits
+        ;;; for the next division step.
+        ;;;
+        ;;; From Knuth, our guess is either all ones or x-i and x-i-1
+        ;;; divided by y1, depending on whether x-i and y1 are the
+        ;;; same. We test this guess by determining whether guess*y2
+        ;;; is greater than the three high digits of x minus guess*y1
+        ;;; shifted left one digit:
+        ;;;    ------------------------------
+        ;;;   |    x-i    |   x-i-1  | x-i-2 |
+        ;;;    ------------------------------
+        ;;;    ------------------------------
+        ;;; - | g*y1 high | g*y1 low |   0   |
+        ;;;    ------------------------------
+        ;;;             ...               <   guess*y2     ???
+        ;;; If guess*y2 is greater, then we decrement our guess by one
+        ;;; and try again.  This returns a guess that is either
+        ;;; correct or one too large.
+         (bignum-truncate-guess (y1 y2 x-i x-i-1 x-i-2)
+           (declare (type bignum-element-type y1 y2 x-i x-i-1 x-i-2))
+           (let ((guess (if (%digit-compare x-i y1)
+                            all-ones-digit
+                            (%bigfloor x-i x-i-1 y1))))
+             (declare (type bignum-element-type guess))
+             (loop
+                 (multiple-value-bind (high-guess*y1 low-guess*y1)
+                     (%multiply guess y1)
+                   (declare (type bignum-element-type low-guess*y1
+                                  high-guess*y1))
+                   (multiple-value-bind (high-guess*y2 low-guess*y2)
+                       (%multiply guess y2)
+                     (declare (type bignum-element-type high-guess*y2
+                                    low-guess*y2))
+                     (multiple-value-bind (middle-digit borrow)
+                         (%subtract-with-borrow x-i-1 low-guess*y1 1)
+                       (declare (type bignum-element-type middle-digit)
+                                (fixnum borrow))
+                       ;; Supplying borrow of 1 means there was no
+                       ;; borrow, and we know x-i-2 minus 0 requires
+                       ;; no borrow.
+                       (let ((high-digit (%subtract-with-borrow x-i
+                                                                high-guess*y1
+                                                                borrow)))
+                         (declare (type bignum-element-type high-digit))
+                         (if (and (%digit-compare high-digit 0)
+                                  (or (%digit-greater high-guess*y2
+                                                      middle-digit)
+                                      (and (%digit-compare middle-digit
+                                                           high-guess*y2)
+                                           (%digit-greater low-guess*y2
+                                                           x-i-2))))
+                             (setf guess (%subtract-with-borrow guess 1 1))
+                             (return guess)))))))))
+        ;;; Divide TRUNCATE-X by TRUNCATE-Y, returning the quotient
+        ;;; and destructively modifying TRUNCATE-X so that it holds
+        ;;; the remainder.
+        ;;;
+        ;;; LEN-X and LEN-Y tell us how much of the buffers we care about.
+        ;;;
+        ;;; TRUNCATE-X definitely has at least three digits, and it has one
+        ;;; more than TRUNCATE-Y. This keeps i, i-1, i-2, and low-x-digit
+        ;;; happy. Thanks to SHIFT-AND-STORE-TRUNCATE-BUFFERS.
+         (return-quotient-leaving-remainder (len-x len-y)
+           (declare (type bignum-index len-x len-y))
+           (let* ((len-q (- len-x len-y))
+                  ;; Add one for extra sign digit in case high bit is on.
+                  (q (%allocate-bignum (1+ len-q)))
+                  (k (1- len-q))
+                  (y1 (%bignum-ref truncate-y (1- len-y)))
+                  (y2 (%bignum-ref truncate-y (- len-y 2)))
+                  (i (1- len-x))
+                  (i-1 (1- i))
+                  (i-2 (1- i-1))
+                  (low-x-digit (- i len-y)))
+             (declare (type bignum-index len-q k i i-1 i-2 low-x-digit)
+                      (type bignum-element-type y1 y2))
+             (loop
+                 (setf (%bignum-ref q k)
+                       (try-bignum-truncate-guess
+                        ;; This modifies TRUNCATE-X. Must access
+                        ;; elements each pass.
+                        (bignum-truncate-guess y1 y2
+                                               (%bignum-ref truncate-x i)
+                                               (%bignum-ref truncate-x i-1)
+                                               (%bignum-ref truncate-x i-2))
+                        len-y low-x-digit))
+                 (cond ((zerop k) (return))
+                       (t (decf k)
+                          (decf low-x-digit)
+                          (shiftf i i-1 i-2 (1- i-2)))))
+             q))
+        ;;; This takes a digit guess, multiplies it by TRUNCATE-Y for a
+        ;;; result one greater in length than LEN-Y, and subtracts this result
+        ;;; from TRUNCATE-X. LOW-X-DIGIT is the first digit of X to start
+        ;;; the subtraction, and we know X is long enough to subtract a LEN-Y
+        ;;; plus one length bignum from it. Next we check the result of the
+        ;;; subtraction, and if the high digit in X became negative, then our
+        ;;; guess was one too big. In this case, return one less than GUESS
+        ;;; passed in, and add one value of Y back into X to account for
+        ;;; subtracting one too many. Knuth shows that the guess is wrong on
+        ;;; the order of 3/b, where b is the base (2 to the digit-size power)
+        ;;; -- pretty rarely.
+         (try-bignum-truncate-guess (guess len-y low-x-digit)
+           (declare (type bignum-index low-x-digit len-y)
+                    (type bignum-element-type guess))
+           (let ((carry-digit 0)
+                 (borrow 1)
+                 (i low-x-digit))
+             (declare (type bignum-element-type carry-digit)
+                      (type bignum-index i)
+                      (fixnum borrow))
+             ;; Multiply guess and divisor, subtracting from dividend
+             ;; simultaneously.
+             (dotimes (j len-y)
+               (multiple-value-bind (high-digit low-digit)
+                   (%multiply-and-add guess
+                                      (%bignum-ref truncate-y j)
+                                      carry-digit)
+                 (declare (type bignum-element-type high-digit low-digit))
+                 (setf carry-digit high-digit)
+                 (multiple-value-bind (x temp-borrow)
+                     (%subtract-with-borrow (%bignum-ref truncate-x i)
+                                            low-digit
+                                            borrow)
+                   (declare (type bignum-element-type x)
+                            (fixnum temp-borrow))
+                   (setf (%bignum-ref truncate-x i) x)
+                   (setf borrow temp-borrow)))
+               (incf i))
+             (setf (%bignum-ref truncate-x i)
+                   (%subtract-with-borrow (%bignum-ref truncate-x i)
+                                          carry-digit borrow))
+             ;; See whether guess is off by one, adding one
+             ;; Y back in if necessary.
+             (cond ((%digit-0-or-plusp (%bignum-ref truncate-x i))
+                    guess)
+                   (t
+                    ;; If subtraction has negative result, add one
+                    ;; divisor value back in. The guess was one too
+                    ;; large in magnitude.
+                    (let ((i low-x-digit)
+                          (carry 0))
+                      (dotimes (j len-y)
+                        (multiple-value-bind (v k)
+                            (%add-with-carry (%bignum-ref truncate-y j)
+                                             (%bignum-ref truncate-x i)
+                                             carry)
+                          (declare (type bignum-element-type v))
+                          (setf (%bignum-ref truncate-x i) v)
+                          (setf carry k))
+                        (incf i))
+                      (setf (%bignum-ref truncate-x i)
+                            (%add-with-carry (%bignum-ref truncate-x i)
+                                             0 carry)))
+                    (%subtract-with-borrow guess 1 1)))))
+        ;;; This returns the amount to shift y to place a one in the
+        ;;; second highest bit. Y must be positive. If the last digit
+        ;;; of y is zero, then y has a one in the previous digit's
+        ;;; sign bit, so we know it will take one less than digit-size
+        ;;; to get a one where we want. Otherwise, we count how many
+        ;;; right shifts it takes to get zero; subtracting this value
+        ;;; from digit-size tells us how many high zeros there are
+        ;;; which is one more than the shift amount sought.
+        ;;;
+        ;;; Note: This is exactly the same as one less than the
+        ;;; integer-length of the last digit subtracted from the
+        ;;; digit-size.
+        ;;;
+        ;;; We shift y to make it sufficiently large that doing the
+        ;;; 2*digit-size by digit-size %BIGFLOOR calls ensures the quotient and
+        ;;; remainder fit in digit-size.
+         (shift-y-for-truncate (y)
+           (let* ((len (%bignum-length y))
+                  (last (%bignum-ref y (1- len))))
+             (declare (type bignum-index len)
+                      (type bignum-element-type last))
+             (- digit-size (integer-length last) 1)))
+         ;;; Stores two bignums into the truncation bignum buffers,
+         ;;; shifting them on the way in. This assumes x and y are
+         ;;; positive and at least two in length, and it assumes
+         ;;; truncate-x and truncate-y are one digit longer than x and
+         ;;; y.
+         (shift-and-store-truncate-buffers (x len-x y len-y shift)
+           (declare (type bignum-index len-x len-y)
+                    (type (integer 0 (#.digit-size)) shift))
+           (cond ((zerop shift)
+                  (bignum-replace truncate-x x :end1 len-x)
+                  (bignum-replace truncate-y y :end1 len-y))
+                 (t
+                  (bignum-ashift-left-unaligned x 0 shift (1+ len-x)
+                                                truncate-x)
+                  (bignum-ashift-left-unaligned y 0 shift (1+ len-y)
+                                                truncate-y))))) ;; LABELS
+      ;;; Divide X by Y returning the quotient and remainder. In the
+      ;;; general case, we shift Y to set up for the algorithm, and we
+      ;;; use two buffers to save consing intermediate values. X gets
+      ;;; destructively modified to become the remainder, and we have
+      ;;; to shift it to account for the initial Y shift. After we
+      ;;; multiple bind q and r, we first fix up the signs and then
+      ;;; return the normalized results.
+      (let* ((x-plusp (%bignum-0-or-plusp x (%bignum-length x)))
+             (y-plusp (%bignum-0-or-plusp y (%bignum-length y)))
+             (x (if x-plusp x (negate-bignum x nil)))
+             (y (if y-plusp y (negate-bignum y nil)))
+             (len-x (%bignum-length x))
+             (len-y (%bignum-length y)))
+        (multiple-value-bind (q r)
+            (cond ((< len-y 2)
+                   (bignum-truncate-single-digit x len-x y))
+                  ((plusp (bignum-compare y x))
+                   (let ((res (%allocate-bignum len-x)))
+                     (dotimes (i len-x)
+                       (setf (%bignum-ref res i) (%bignum-ref x i)))
+                     (values 0 res)))
+                  (t
+                   (let ((len-x+1 (1+ len-x)))
+                     (setf truncate-x (%allocate-bignum len-x+1))
+                     (setf truncate-y (%allocate-bignum (1+ len-y)))
+                     (let ((y-shift (shift-y-for-truncate y)))
+                       (shift-and-store-truncate-buffers x len-x y
+                                                         len-y y-shift)
+                       (values (return-quotient-leaving-remainder len-x+1
+                                                                  len-y)
+                               ;; Now that RETURN-QUOTIENT-LEAVING-REMAINDER
+                               ;; has executed, we just tidy up the remainder
+                               ;; (in TRUNCATE-X) and return it.
+                               (cond
+                                 ((zerop y-shift)
+                                  (let ((res (%allocate-bignum len-y)))
+                                    (declare (type bignum-type res))
+                                    (bignum-replace res truncate-x :end2 len-y)
+                                    (%normalize-bignum res len-y)))
+                                 (t
+                                  (shift-right-unaligned
+                                   truncate-x 0 y-shift len-y
+                                   ((= j res-len-1)
+                                    (setf (%bignum-ref res j)
+                                          (%ashr (%bignum-ref truncate-x i)
+                                                 y-shift))
+                                    (%normalize-bignum res res-len))
+                                   res))))))))
+          (let ((quotient (cond ((eq x-plusp y-plusp) q)
+                                ((typep q 'fixnum) (the fixnum (- q)))
+                                (t (negate-bignum-in-place q))))
+                (rem (cond (x-plusp r)
+                           ((typep r 'fixnum) (the fixnum (- r)))
+                           (t (negate-bignum-in-place r)))))
+            (values (if (typep quotient 'fixnum)
+                        quotient
+                        (%normalize-bignum quotient (%bignum-length quotient)))
+                    (if (typep rem 'fixnum)
+                        rem
+                        (%normalize-bignum rem (%bignum-length rem))))))))))
+
 
-;;;; %FLOOR primitive for BIGNUM-TRUNCATE
-
-;;; When a machine leaves out a 64-bit by 32-bit divide instruction (that is,
-;;; two bignum-digits divided by one), we have to roll our own (the hard way).
-;;; Basically, we treat the operation as four 16-bit digits divided by two
-;;; 16-bit digits. This means we have duplicated most of the code above to do
-;;; this nearly general 16-bit digit bignum divide, but we've unrolled loops
-;;; and made use of other properties of this specific divide situation.
-
-;;;; %FLOOR for machines with a 32x32 divider.
-
-#!-sb-fluid
-(declaim (inline 32x16-subtract-with-borrow 32x16-add-with-carry
-		 32x16-divide 32x16-multiply 32x16-multiply-split))
-
-#!+32x16-divide
-(defconstant 32x16-base-1 #xFFFF)
-
-;;; This is similar to %SUBTRACT-WITH-BORROW. It returns a 16-bit difference
-;;; and a borrow. Returning a 1 for the borrow means there was no borrow, and
-;;; 0 means there was one.
-#!+32x16-divide
-(defun 32x16-subtract-with-borrow (a b borrow)
-  (declare (type (unsigned-byte 16) a b)
-	   (type (integer 0 1) borrow))
-  (let ((diff (+ (- a b) borrow 32x16-base-1)))
-    (declare (type (unsigned-byte 17) diff))
-    (values (logand diff #xFFFF)
-	    (ash diff -16))))
-
-;;; This adds a and b, 16-bit quantities, with the carry k. It returns a
-;;; 16-bit sum and a second value, 0 or 1, indicating whether there was a
-;;; carry.
-#!+32x16-divide
-(defun 32x16-add-with-carry (a b k)
-  (declare (type (unsigned-byte 16) a b)
-	   (type (integer 0 1) k))
-  (let ((res (the fixnum (+ a b k))))
-    (declare (type (unsigned-byte 17) res))
-    (if (zerop (the fixnum (logand #x10000 res)))
-	(values res 0)
-	(values (the (unsigned-byte 16) (logand #xFFFF res))
-		1))))
-
-;;; This is probably a 32-bit by 32-bit divide instruction.
-#!+32x16-divide
-(defun 32x16-divide (a b c)
-  (declare (type (unsigned-byte 16) a b c))
-  (floor (the bignum-element-type
-	      (logior (the bignum-element-type (ash a 16))
-		      b))
-	 c))
-
-;;; This basically exists since we know the answer won't overflow
-;;; bignum-element-type. It's probably just a basic multiply instruction, but
-;;; it can't cons an intermediate bignum. The result goes in a non-descriptor
-;;; register.
-#!+32x16-divide
-(defun 32x16-multiply (a b)
-  (declare (type (unsigned-byte 16) a b))
-  (the bignum-element-type (* a b)))
-
-;;; This multiplies a and b, 16-bit quantities, and returns the result as two
-;;; 16-bit quantities, high and low.
-#!+32x16-divide
-(defun 32x16-multiply-split (a b)
-  (let ((res (32x16-multiply a b)))
-    (declare (the bignum-element-type res))
-    (values (the (unsigned-byte 16) (logand #xFFFF (ash res -16)))
-	    (the (unsigned-byte 16) (logand #xFFFF res)))))
-
-;;; The %FLOOR below uses this buffer the same way BIGNUM-TRUNCATE uses
-;;; *truncate-x*. There's no y buffer since we pass around the two 16-bit
-;;; digits and use them slightly differently than the general truncation
-;;; algorithm above.
-#!+32x16-divide
-(defvar *32x16-truncate-x* (make-array 4 :element-type '(unsigned-byte 16)
-				       :initial-element 0))
-
-;;; This does the same thing as the %FLOOR above, but it does it at Lisp level
-;;; when there is no 64x32-bit divide instruction on the machine.
-;;;
-;;; It implements the higher level tactics of BIGNUM-TRUNCATE, but it makes use
-;;; of special situation provided, four 16-bit digits divided by two 16-bit
-;;; digits.
-#!+32x16-divide
-(defun %floor (a b c)
-  (declare (type bignum-element-type a b c))
-  ;; Setup *32x16-truncate-x* buffer from a and b.
-  (setf (aref *32x16-truncate-x* 0)
-	(the (unsigned-byte 16) (logand #xFFFF b)))
-  (setf (aref *32x16-truncate-x* 1)
-	(the (unsigned-byte 16)
-	     (logand #xFFFF
-		     (the (unsigned-byte 16) (ash b -16)))))
-  (setf (aref *32x16-truncate-x* 2)
-	(the (unsigned-byte 16) (logand #xFFFF a)))
-  (setf (aref *32x16-truncate-x* 3)
-	(the (unsigned-byte 16)
-	     (logand #xFFFF
-		     (the (unsigned-byte 16) (ash a -16)))))
-  ;; From DO-TRUNCATE, but unroll the loop.
-  (let* ((y1 (logand #xFFFF (ash c -16)))
-	 (y2 (logand #xFFFF c))
-	 (q (the bignum-element-type
-		 (ash (32x16-try-bignum-truncate-guess
-		       (32x16-truncate-guess y1 y2
-					     (aref *32x16-truncate-x* 3)
-					     (aref *32x16-truncate-x* 2)
-					     (aref *32x16-truncate-x* 1))
-		       y1 y2 1)
-		      16))))
-    (declare (type bignum-element-type q)
-	     (type (unsigned-byte 16) y1 y2))
-    (values (the bignum-element-type
-		 (logior q
-			 (the (unsigned-byte 16)
-			      (32x16-try-bignum-truncate-guess
-			       (32x16-truncate-guess
-				y1 y2
-				(aref *32x16-truncate-x* 2)
-				(aref *32x16-truncate-x* 1)
-				(aref *32x16-truncate-x* 0))
-			       y1 y2 0))))
-	    (the bignum-element-type
-		 (logior (the bignum-element-type
-			      (ash (aref *32x16-truncate-x* 1) 16))
-			 (the (unsigned-byte 16)
-			      (aref *32x16-truncate-x* 0)))))))
-
-;;; This is similar to TRY-BIGNUM-TRUNCATE-GUESS, but this unrolls the two
-;;; loops. This also substitutes for %DIGIT-0-OR-PLUSP the equivalent
-;;; expression without any embellishment or pretense of abstraction. The first
-;;; loop is unrolled, but we've put the body of the loop into the function
-;;; 32X16-TRY-GUESS-ONE-RESULT-DIGIT.
-#!+32x16-divide
-(defun 32x16-try-bignum-truncate-guess (guess y-high y-low low-x-digit)
-  (declare (type bignum-index low-x-digit)
-	   (type (unsigned-byte 16) guess y-high y-low))
-  (let ((high-x-digit (+ 2 low-x-digit)))
-    ;; Multiply guess and divisor, subtracting from dividend simultaneously.
-    (multiple-value-bind (guess*y-hold carry borrow)
-	(32x16-try-guess-one-result-digit guess y-low 0 0 1 low-x-digit)
-      (declare (type (unsigned-byte 16) guess*y-hold)
-	       (fixnum carry borrow))
-      (multiple-value-bind (guess*y-hold carry borrow)
-	  (32x16-try-guess-one-result-digit guess y-high guess*y-hold
-					    carry borrow (1+ low-x-digit))
-	(declare (type (unsigned-byte 16) guess*y-hold)
-		 (fixnum borrow)
-		 (ignore carry))
-	(setf (aref *32x16-truncate-x* high-x-digit)
-	      (32x16-subtract-with-borrow (aref *32x16-truncate-x* high-x-digit)
-					  guess*y-hold borrow))))
-    ;; See whether guess is off by one, adding one Y back in if necessary.
-    (cond ((zerop (logand #x8000 (aref *32x16-truncate-x* high-x-digit)))
-	   ;; The subtraction result is zero or positive.
-	   guess)
-	  (t
-	   ;; If subtraction has negative result, add one divisor value back
-	   ;; in. The guess was one too large in magnitude.
-	   (multiple-value-bind (v carry)
-	       (32x16-add-with-carry y-low
-				     (aref *32x16-truncate-x* low-x-digit)
-				     0)
-	     (declare (type (unsigned-byte 16) v))
-	     (setf (aref *32x16-truncate-x* low-x-digit) v)
-	     (multiple-value-bind (v carry)
-		 (32x16-add-with-carry y-high
-				       (aref *32x16-truncate-x*
-					     (1+ low-x-digit))
-				       carry)
-	       (setf (aref *32x16-truncate-x* (1+ low-x-digit)) v)
-	       (setf (aref *32x16-truncate-x* high-x-digit)
-		     (32x16-add-with-carry (aref *32x16-truncate-x* high-x-digit)
-					   carry 0))))
-	   (if (zerop (logand #x8000 guess))
-	       (1- guess)
-	       (1+ guess))))))
-
-;;; This is similar to the body of the loop in TRY-BIGNUM-TRUNCATE-GUESS that
-;;; multiplies the guess by y and subtracts the result from x simultaneously.
-;;; This returns the digit remembered as part of the multiplication, the carry
-;;; from additions done on behalf of the multiplication, and the borrow from
-;;; doing the subtraction.
-#!+32x16-divide
-(defun 32x16-try-guess-one-result-digit (guess y-digit guess*y-hold
-					 carry borrow x-index)
-  (multiple-value-bind (high-digit low-digit)
-      (32x16-multiply-split guess y-digit)
-    (declare (type (unsigned-byte 16) high-digit low-digit))
-    (multiple-value-bind (low-digit temp-carry)
-	(32x16-add-with-carry low-digit guess*y-hold carry)
-      (declare (type (unsigned-byte 16) low-digit))
-      (multiple-value-bind (high-digit temp-carry)
-	  (32x16-add-with-carry high-digit temp-carry 0)
-	(declare (type (unsigned-byte 16) high-digit))
-	(multiple-value-bind (x temp-borrow)
-	    (32x16-subtract-with-borrow (aref *32x16-truncate-x* x-index)
-					low-digit borrow)
-	  (declare (type (unsigned-byte 16) x))
-	  (setf (aref *32x16-truncate-x* x-index) x)
-	  (values high-digit temp-carry temp-borrow))))))
-
-;;; This is similar to BIGNUM-TRUNCATE-GUESS, but instead of computing the
-;;; guess exactly as described in the its comments (digit by digit), this
-;;; massages the 16-bit quantities into 32-bit quantities and performs the
-#!+32x16-divide
-(defun 32x16-truncate-guess (y1 y2 x-i x-i-1 x-i-2)
-  (declare (type (unsigned-byte 16) y1 y2 x-i x-i-1 x-i-2))
-  (let ((guess (if (= x-i y1)
-		   #xFFFF
-		   (32x16-divide x-i x-i-1 y1))))
-    (declare (type (unsigned-byte 16) guess))
-    (loop
-      (let* ((guess*y1 (the bignum-element-type
-			    (ash (logand #xFFFF
-					 (the bignum-element-type
-					      (32x16-multiply guess y1)))
-				 16)))
-	     (x-y (%subtract-with-borrow
-		   (the bignum-element-type
-			(logior (the bignum-element-type
-				     (ash x-i-1 16))
-				x-i-2))
-		   guess*y1
-		   1))
-	     (guess*y2 (the bignum-element-type (%multiply guess y2))))
-	(declare (type bignum-element-type guess*y1 x-y guess*y2))
-	(if (%digit-greater guess*y2 x-y)
-	    (decf guess)
-	    (return guess))))))
+;;;; There used to be a pile of code for implementing division for bignum digits
+;;;; for machines that don't have a 2*digit-size by digit-size divide instruction.
+;;;; This happens to be most machines, but all the SBCL ports seem to be content
+;;;; to implement SB-BIGNUM:%BIGFLOOR as a VOP rather than using the code here.
+;;;; So it's been deleted.  --njf, 2007-02-04
 
 ;;;; general utilities
 
-;;; Allocate a single word bignum that holds fixnum. This is useful when
-;;; we are trying to mix fixnum and bignum operands.
-#!-sb-fluid (declaim (inline make-small-bignum))
-(defun make-small-bignum (fixnum)
-  (let ((res (%allocate-bignum 1)))
-    (setf (%bignum-ref res 0) (%fixnum-to-digit fixnum))
-    res))
-
 ;;; Internal in-place operations use this to fixup remaining digits in the
 ;;; incoming data, such as in-place shifting. This is basically the same as
 ;;; the first form in %NORMALIZE-BIGNUM, but we return the length of the buffer
@@ -2235,16 +1874,16 @@ IS LESS EFFICIENT BUT EASIER TO MAINTAIN. BILL SAYS THIS CODE CERTAINLY WORKS!
 #!-sb-fluid (declaim (sb!ext:maybe-inline %normalize-bignum-buffer))
 (defun %normalize-bignum-buffer (result len)
   (declare (type bignum-type result)
-	   (type bignum-index len))
+           (type bignum-index len))
   (unless (= len 1)
     (do ((next-digit (%bignum-ref result (- len 2))
-		     (%bignum-ref result (- len 2)))
-	 (sign-digit (%bignum-ref result (1- len)) next-digit))
-	((not (zerop (logxor sign-digit (%ashr next-digit (1- digit-size))))))
-	(decf len)
-	(setf (%bignum-ref result len) 0)	
-	(when (= len 1)
-	      (return))))
+                     (%bignum-ref result (- len 2)))
+         (sign-digit (%bignum-ref result (1- len)) next-digit))
+        ((not (zerop (logxor sign-digit (%ashr next-digit (1- digit-size))))))
+        (decf len)
+        (setf (%bignum-ref result len) 0)
+        (when (= len 1)
+              (return))))
   len)
 
 ;;; This drops the last digit if it is unnecessary sign information. It repeats
@@ -2256,26 +1895,27 @@ IS LESS EFFICIENT BUT EASIER TO MAINTAIN. BILL SAYS THIS CODE CERTAINLY WORKS!
 ;;; we do have a fixnum, shift it over for the two low-tag bits.
 (defun %normalize-bignum (result len)
   (declare (type bignum-type result)
-	   (type bignum-index len)
-	   (inline %normalize-bignum-buffer))
+           (type bignum-index len)
+           (inline %normalize-bignum-buffer))
   (let ((newlen (%normalize-bignum-buffer result len)))
     (declare (type bignum-index newlen))
     (unless (= newlen len)
       (%bignum-set-length result newlen))
     (if (= newlen 1)
-	(let ((digit (%bignum-ref result 0)))
-	  (if (= (%ashr digit 29) (%ashr digit (1- digit-size)))
-	      (%fixnum-digit-with-correct-sign digit)
-	      result))
-	result)))
+        (let ((digit (%bignum-ref result 0)))
+          (if (= (%ashr digit sb!vm:n-positive-fixnum-bits)
+                 (%ashr digit (1- digit-size)))
+              (%fixnum-digit-with-correct-sign digit)
+              result))
+        result)))
 
 ;;; This drops the last digit if it is unnecessary sign information. It
 ;;; repeats this as needed, possibly ending with a fixnum magnitude but never
 ;;; returning a fixnum.
 (defun %mostly-normalize-bignum (result len)
   (declare (type bignum-type result)
-	   (type bignum-index len)
-	   (inline %normalize-bignum-buffer))
+           (type bignum-index len)
+           (inline %normalize-bignum-buffer))
   (let ((newlen (%normalize-bignum-buffer result len)))
     (declare (type bignum-index newlen))
     (unless (= newlen len)
@@ -2291,8 +1931,8 @@ IS LESS EFFICIENT BUT EASIER TO MAINTAIN. BILL SAYS THIS CODE CERTAINLY WORKS!
     (dotimes (i (%bignum-length x))
       (declare (type index i))
       (let ((xi (%bignum-ref x i)))
-	(mixf result
-	      (logand most-positive-fixnum
-		      xi
-		      (ash xi -7)))))
+        (mixf result
+              (logand most-positive-fixnum
+                      (logxor xi
+                              (ash xi -7))))))
     result))