X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;ds=sidebyside;f=src%2Fcode%2Firrat.lisp;h=fe1362035d61e32344b06b5a8bbc572f9ed2b23b;hb=860543cc7ba0266e41e1d41ac9b6a208f3795f1a;hp=9acba103f76b4602672720b01397e4428319364b;hpb=dae7439918b773ae820d741445c0e8f5bbcee7cb;p=sbcl.git

diff --git a/src/code/irrat.lisp b/src/code/irrat.lisp
index 9acba10..fe13620 100644
--- a/src/code/irrat.lisp
+++ b/src/code/irrat.lisp
@@ -14,8 +14,9 @@
 
 ;;;; miscellaneous constants, utility functions, and macros
 
-(defconstant pi 3.14159265358979323846264338327950288419716939937511L0)
-;(defconstant e 2.71828182845904523536028747135266249775724709369996L0)
+(defconstant pi
+  #!+long-float 3.14159265358979323846264338327950288419716939937511l0
+  #!-long-float 3.14159265358979323846264338327950288419716939937511d0)
 
 ;;; Make these INLINE, since the call to C is at least as compact as a
 ;;; Lisp call, and saves number consing to boot.
@@ -269,18 +270,54 @@
 	     (* base power)
 	     (exp (* power (log base)))))))))
 
+;;; FIXME: Maybe rename this so that it's clearer that it only works
+;;; on integers?
+(defun log2 (x)
+  (declare (type integer x))
+  ;; CMUCL comment:
+  ;;
+  ;;   Write x = 2^n*f where 1/2 < f <= 1.  Then log2(x) = n +
+  ;;   log2(f).  So we grab the top few bits of x and scale that
+  ;;   appropriately, take the log of it and add it to n.
+  ;;
+  ;; Motivated by an attempt to get LOG to work better on bignums.
+  (let ((n (integer-length x)))
+    (if (< n sb!vm:double-float-digits)
+	(log (coerce x 'double-float) 2.0d0)
+	(let ((f (ldb (byte sb!vm:double-float-digits
+			    (- n sb!vm:double-float-digits))
+		      x)))
+	  (+ n (log (scale-float (coerce f 'double-float)
+				 (- sb!vm:double-float-digits))
+		    2.0d0))))))
+
 (defun log (number &optional (base nil base-p))
   #!+sb-doc
   "Return the logarithm of NUMBER in the base BASE, which defaults to e."
   (if base-p
-      (if (zerop base)
-	  base				; ANSI spec
-	  (/ (log number) (log base)))
+      (cond
+	((zerop base) base) ; ANSI spec
+	((and (typep number '(integer (0) *))
+	      (typep base '(integer (0) *)))
+	 (coerce (/ (log2 number) (log2 base)) 'single-float))
+	(t (/ (log number) (log base))))
       (number-dispatch ((number number))
-	(((foreach fixnum bignum ratio))
+	(((foreach fixnum bignum))
+	 (if (minusp number)
+	     (complex (log (- number)) (coerce pi 'single-float))
+	     (coerce (/ (log2 number) (log (exp 1.0d0) 2.0d0)) 'single-float)))
+	((ratio)
 	 (if (minusp number)
 	     (complex (log (- number)) (coerce pi 'single-float))
-	     (coerce (%log (coerce number 'double-float)) 'single-float)))
+	     (let ((numerator (numerator number))
+		   (denominator (denominator number)))
+	       (if (= (integer-length numerator)
+		      (integer-length denominator))
+		   (coerce (%log1p (coerce (- number 1) 'double-float))
+			   'single-float)
+		   (coerce (/ (- (log2 numerator) (log2 denominator))
+			      (log (exp 1.0d0) 2.0d0))
+			   'single-float)))))
 	(((foreach single-float double-float))
 	 ;; Is (log -0) -infinity (libm.a) or -infinity + i*pi (Kahan)?
 	 ;; Since this doesn't seem to be an implementation issue
@@ -867,13 +904,18 @@
       ;; space 0 to get maybe-inline functions inlined
       (declare (optimize (speed 3) (space 0)))
     (cond ((> (abs x)
-	      #-(or linux hpux) #.(/ (asinh most-positive-double-float) 4d0)
-	      ;; This is more accurate under linux.
-	      #+(or linux hpux) #.(/ (+ (log 2.0d0)
-					(log most-positive-double-float))
-				     4d0))
-              (coerce-to-complex-type (float-sign x)
-                                      (float-sign y) z))
+	      ;; FIXME: this form is hideously broken wrt
+	      ;; cross-compilation portability.  Much else in this
+	      ;; file is too, of course, sometimes hidden by
+	      ;; constant-folding, but this one in particular clearly
+	      ;; depends on host and target
+	      ;; MOST-POSITIVE-DOUBLE-FLOATs being equal.  -- CSR,
+	      ;; 2003-04-20
+	      #.(/ (+ (log 2.0d0)
+		      (log most-positive-double-float))
+		   4d0))
+	   (coerce-to-complex-type (float-sign x)
+				   (float-sign y) z))
 	  (t
 	   (let* ((tv (%tan y))
 		  (beta (+ 1.0d0 (* tv tv)))