From: Stephen Adams <edu/mit/csail/zurich/adams>
Date: Fri, 4 Jul 1997 16:02:18 +0000 (+0000)
Subject: In bignum_remainder, replaced special case for remainder by `1' with a
X-Git-Tag: 20090517-FFI~5087
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=bdb297dc69bbaf6af3ce20c22cf97f0091eb4db4;p=mit-scheme.git

In bignum_remainder, replaced special case for remainder by `1' with a
special case for remainder by small power of two.
---

diff --git a/v7/src/microcode/bignum.c b/v7/src/microcode/bignum.c
index 8a7c70d20..d03fa1505 100644
--- a/v7/src/microcode/bignum.c
+++ b/v7/src/microcode/bignum.c
@@ -1,6 +1,6 @@
 /* -*-C-*-
 
-$Id: bignum.c,v 9.44 1997/04/23 05:40:11 cph Exp $
+$Id: bignum.c,v 9.45 1997/07/04 16:02:18 adams Exp $
 
 Copyright (c) 1989-97 Massachusetts Institute of Technology
 
@@ -426,8 +426,17 @@ DEFUN (bignum_remainder, (numerator, denominator),
 	if ((BIGNUM_LENGTH (denominator)) == 1)
 	  {
 	    bignum_digit_type digit = (BIGNUM_REF (denominator, 0));
-	    if (digit == 1)
-	      return (BIGNUM_ZERO ());
+	    if ((digit & (digit-1)) == 0) /* i.e. digit = 2^k, including 1 */
+	      {
+		bignum_digit_type unsigned_remainder;
+		if (BIGNUM_LENGTH (numerator) == 0)
+		  return (BIGNUM_ZERO ());
+		unsigned_remainder = (digit-1) & (BIGNUM_REF (numerator, 0));
+		if (unsigned_remainder == 0)
+		  return (BIGNUM_ZERO ());
+		return (bignum_digit_to_bignum
+			(unsigned_remainder, BIGNUM_NEGATIVE_P (numerator)));
+	      }
 	    if (digit < BIGNUM_RADIX_ROOT)
 	      return
 		(bignum_remainder_unsigned_small_denominator