1304106Sdelphij/* $OpenBSD: timingsafe_memcmp.c,v 1.2 2015/08/31 02:53:57 guenther Exp $ */ 2304106Sdelphij/* 3304106Sdelphij * Copyright (c) 2014 Google Inc. 4304106Sdelphij * 5304106Sdelphij * Permission to use, copy, modify, and distribute this software for any 6304106Sdelphij * purpose with or without fee is hereby granted, provided that the above 7304106Sdelphij * copyright notice and this permission notice appear in all copies. 8304106Sdelphij * 9304106Sdelphij * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10304106Sdelphij * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11304106Sdelphij * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12304106Sdelphij * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13304106Sdelphij * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14304106Sdelphij * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15304106Sdelphij * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16304106Sdelphij */ 17304106Sdelphij 18304106Sdelphij#include <sys/cdefs.h> 19304106Sdelphij__FBSDID("$FreeBSD: stable/11/lib/libc/string/timingsafe_memcmp.c 319292 2017-05-31 06:47:56Z delphij $"); 20304106Sdelphij 21304106Sdelphij#include <limits.h> 22304106Sdelphij#include <string.h> 23304106Sdelphij 24304106Sdelphijint __timingsafe_memcmp(const void *, const void *, size_t); 25304106Sdelphij 26304106Sdelphijint 27304106Sdelphij__timingsafe_memcmp(const void *b1, const void *b2, size_t len) 28304106Sdelphij{ 29304106Sdelphij const unsigned char *p1 = b1, *p2 = b2; 30304106Sdelphij size_t i; 31304106Sdelphij int res = 0, done = 0; 32304106Sdelphij 33304106Sdelphij for (i = 0; i < len; i++) { 34304106Sdelphij /* lt is -1 if p1[i] < p2[i]; else 0. */ 35304106Sdelphij int lt = (p1[i] - p2[i]) >> CHAR_BIT; 36304106Sdelphij 37304106Sdelphij /* gt is -1 if p1[i] > p2[i]; else 0. */ 38304106Sdelphij int gt = (p2[i] - p1[i]) >> CHAR_BIT; 39304106Sdelphij 40304106Sdelphij /* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */ 41304106Sdelphij int cmp = lt - gt; 42304106Sdelphij 43304106Sdelphij /* set res = cmp if !done. */ 44304106Sdelphij res |= cmp & ~done; 45304106Sdelphij 46304106Sdelphij /* set done if p1[i] != p2[i]. */ 47304106Sdelphij done |= lt | gt; 48304106Sdelphij } 49304106Sdelphij 50304106Sdelphij return (res); 51304106Sdelphij} 52304106Sdelphij 53304106Sdelphij__weak_reference(__timingsafe_memcmp, timingsafe_memcmp); 54