From: Chris Hanson <org/chris-hanson/cph>
Date: Wed, 10 Jul 1991 20:06:18 +0000 (+0000)
Subject: Handle (/ 0 X) specially to guarantee that result is exact zero even
X-Git-Tag: 20090517-FFI~10472
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=c3633079a9e13fde56b4d1d0dc4908feca41bb78;p=mit-scheme.git

Handle (/ 0 X) specially to guarantee that result is exact zero even
when X is inexact.
---

diff --git a/v7/src/runtime/arith.scm b/v7/src/runtime/arith.scm
index 3e13496d1..0913afefe 100644
--- a/v7/src/runtime/arith.scm
+++ b/v7/src/runtime/arith.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/arith.scm,v 1.20 1991/05/06 18:08:24 jinx Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/runtime/arith.scm,v 1.21 1991/07/10 20:06:18 cph Exp $
 
 Copyright (c) 1989-91 Massachusetts Institute of Technology
 
@@ -789,7 +789,6 @@ MIT in each case. |#
 		    (,rat:op X Y)))))))
   (define-standard-binary real:+ flo:+ (copy rat:+))
   (define-standard-binary real:- flo:- (copy rat:-))
-  (define-standard-binary real:/ flo:/ (copy rat:/))
   (define-standard-binary real:rationalize
     flo:rationalize
     rat:rationalize)
@@ -847,6 +846,11 @@ MIT in each case. |#
 	((rat:zero? x) x)
 	((flonum? y) (flo:* (rat:->flonum x) y))
 	(else ((copy rat:*) x y))))
+
+(define (real:/ x y)
+  (cond ((flonum? x) (flo:/ x (if (flonum? y) y (rat:->flonum y))))
+	((flonum? y) (if (rat:zero? x) x (flo:/ (rat:->flonum x) y)))
+	(else ((copy rat:/) x y))))
 
 (define (real:even? n)
   ((copy int:even?)