From b2326b89f4553fc7355e742b6da8aa14d726ee4e Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Sun, 9 Sep 2018 18:42:35 -0400
Subject: [PATCH] Issue #276 - Possible fix

Do not perform multiplication until we are sure the operation will not over/under flow.
---
 runtime.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/runtime.c b/runtime.c
index d43aab0b..ae98b2ac 100644
--- a/runtime.c
+++ b/runtime.c
@@ -3053,9 +3053,20 @@ static int Cyc_checked_sub(int x, int y, int *result)
 // Code from http://stackoverflow.com/q/1815367/101258
 static int Cyc_checked_mul(int x, int y, int *result)
 {
+//  *result = x * y;
+//  return (*result != 0 && (*result)/x != y) || // Overflow
+//         (*result > CYC_FIXNUM_MAX) ||
+//         (*result < CYC_FIXNUM_MIN);
+  uint xu, yu, c;
+  c = 1UL<<31UL;
+  xu = x < 0 ? -1 : x;
+  yu = y < 0 ? -1 : y;
+
+  if (yu != 0 && xu > (c / yu)) return 1; // Overflow
+
   *result = x * y;
-  return (*result != 0 && (*result)/x != y) || // Overflow
-         (*result > CYC_FIXNUM_MAX) ||
+
+  return (*result > CYC_FIXNUM_MAX) ||
          (*result < CYC_FIXNUM_MIN);
 }