1*854023f0SXin LI /* $OpenBSD: timingsafe_memcmp.c,v 1.2 2015/08/31 02:53:57 guenther Exp $ */ 2*854023f0SXin LI /* 3*854023f0SXin LI * Copyright (c) 2014 Google Inc. 4*854023f0SXin LI * 5*854023f0SXin LI * Permission to use, copy, modify, and distribute this software for any 6*854023f0SXin LI * purpose with or without fee is hereby granted, provided that the above 7*854023f0SXin LI * copyright notice and this permission notice appear in all copies. 8*854023f0SXin LI * 9*854023f0SXin LI * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10*854023f0SXin LI * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11*854023f0SXin LI * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12*854023f0SXin LI * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13*854023f0SXin LI * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14*854023f0SXin LI * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15*854023f0SXin LI * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16*854023f0SXin LI */ 17*854023f0SXin LI 18*854023f0SXin LI #include <sys/cdefs.h> 19*854023f0SXin LI __FBSDID("$FreeBSD$"); 20*854023f0SXin LI 21*854023f0SXin LI #include <limits.h> 22*854023f0SXin LI #include <string.h> 23*854023f0SXin LI 24*854023f0SXin LI int __timingsafe_memcmp(const void *, const void *, size_t); 25*854023f0SXin LI 26*854023f0SXin LI int 27*854023f0SXin LI __timingsafe_memcmp(const void *b1, const void *b2, size_t len) 28*854023f0SXin LI { 29*854023f0SXin LI const unsigned char *p1 = b1, *p2 = b2; 30*854023f0SXin LI size_t i; 31*854023f0SXin LI int res = 0, done = 0; 32*854023f0SXin LI 33*854023f0SXin LI for (i = 0; i < len; i++) { 34*854023f0SXin LI /* lt is -1 if p1[i] < p2[i]; else 0. */ 35*854023f0SXin LI int lt = (p1[i] - p2[i]) >> CHAR_BIT; 36*854023f0SXin LI 37*854023f0SXin LI /* gt is -1 if p1[i] > p2[i]; else 0. */ 38*854023f0SXin LI int gt = (p2[i] - p1[i]) >> CHAR_BIT; 39*854023f0SXin LI 40*854023f0SXin LI /* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */ 41*854023f0SXin LI int cmp = lt - gt; 42*854023f0SXin LI 43*854023f0SXin LI /* set res = cmp if !done. */ 44*854023f0SXin LI res |= cmp & ~done; 45*854023f0SXin LI 46*854023f0SXin LI /* set done if p1[i] != p2[i]. */ 47*854023f0SXin LI done |= lt | gt; 48*854023f0SXin LI } 49*854023f0SXin LI 50*854023f0SXin LI return (res); 51*854023f0SXin LI } 52*854023f0SXin LI 53*854023f0SXin LI __weak_reference(__timingsafe_memcmp, timingsafe_memcmp); 54