From f76b3ad534efbe5ea42319c584e504910752bc9c Mon Sep 17 00:00:00 2001
From: Linas Vepstas <linas@linas.org>
Date: Sun, 4 Jul 2004 03:56:40 +0000
Subject: [PATCH] fix yet another intermediate-math overflow bug. comparing two
 numbers gave incorrect results because intermediate calculation overflowed

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@10153 57a11ea4-9604-0410-9ed3-97b8803252fd
---
 src/engine/gnc-numeric.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/src/engine/gnc-numeric.c b/src/engine/gnc-numeric.c
index 19e4f65e0e..fb73c57d77 100644
--- a/src/engine/gnc-numeric.c
+++ b/src/engine/gnc-numeric.c
@@ -216,24 +216,36 @@ gnc_numeric_positive_p(gnc_numeric a)
  ********************************************************************/
 
 int
-gnc_numeric_compare(gnc_numeric a, gnc_numeric b) {
-  gint64 ab, ba;
+gnc_numeric_compare(gnc_numeric a, gnc_numeric b) 
+{
+  gint64 aa, bb;
 
-  if(gnc_numeric_check(a) || gnc_numeric_check(b)) {
+  if(gnc_numeric_check(a) || gnc_numeric_check(b)) 
+  {
     return 0;
   }
-  ab = a.num * b.denom;
-  ba = b.num * a.denom;
 
-  if(ab == ba) {
-    return 0;
-  }
-  else if(ab > ba) {
-    return 1;
-  }
-  else {
+  if (a.denom == b.denom)
+  {
+    if(a.num == b.num) return 0;
+    if(a.num > b.num) return 1;
     return -1;
   }
+
+  if  ((a.denom > 0) && (b.denom > 0))
+  {
+    /* Avoid overflows using 128-bit intermediate math */
+    qofint128 l = mult128 (a.num, b.denom);
+    qofint128 r = mult128 (b.num, a.denom);
+    return cmp128 (l,r);
+  }
+
+  aa = a.num * a.denom;
+  bb = b.num * b.denom;
+
+  if(aa == bb) return 0;
+  if(aa > bb) return 1;
+  return -1;
 }