Fcalva/cyclone
1
0
Fork 0
mirror of https://github.com/justinethier/cyclone.git synced 2025-05-24 20:45:06 +02:00
Code Issues Projects Releases Packages Wiki Activity Actions

Issue #276 - Improve overflow detection for multiplication

Browse source
This commit is contained in:
Justin Ethier 2018-09-10 13:29:30 -04:00
parent b2326b89f4
commit b41971e187
1 changed files with 5 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
runtime.c
View file

@ -3050,17 +3050,14 @@ static int Cyc_checked_sub(int x, int y, int *result)
return ((((*result ^ x) & ~(*result ^ y)) >> 30) != 0); return ((((*result ^ x) & ~(*result ^ y)) >> 30) != 0);
} }
// Code from http://stackoverflow.com/q/1815367/101258
static int Cyc_checked_mul(int x, int y, int *result) static int Cyc_checked_mul(int x, int y, int *result)
{ {
// *result = x * y; // Avoid undefined behavior by detecting overflow prior to multiplication
// return (*result != 0 && (*result)/x != y) || // Overflow // Based on code from Hacker's Delight and CHICKEN scheme
// (*result > CYC_FIXNUM_MAX) ||
// (*result < CYC_FIXNUM_MIN);
uint xu, yu, c; uint xu, yu, c;
c = 1UL<<31UL; c = (1UL<<30UL) - 1;
xu = x < 0 ? -1 : x; xu = x < 0 ? -x : x;
yu = y < 0 ? -1 : y; yu = y < 0 ? -y : y;
if (yu != 0 && xu > (c / yu)) return 1; // Overflow if (yu != 0 && xu > (c / yu)) return 1; // Overflow