1 /* 2 * Copyright (C) 2004-2007, 2011, 2012 Internet Systems Consortium, Inc. ("ISC") 3 * Copyright (C) 1999-2001, 2003 Internet Software Consortium. 4 * 5 * Permission to use, copy, modify, and/or distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH 10 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY 11 * AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, 12 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM 13 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE 14 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR 15 * PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 /* $Id$ */ 19 20 /*! \file */ 21 22 #include <config.h> 23 #include <limits.h> 24 #include <isc/string.h> 25 26 /* Making a portable memcmp that has no internal branches and loops always 27 * once for every byte without early-out shortcut has a few challenges. 28 * 29 * Inspired by 'timingsafe_memcmp()' from the BSD system and 30 * https://github.com/libressl-portable/openbsd/blob/master/src/lib/libc/string/timingsafe_memcmp.c 31 * 32 * Sadly, that one is not portable C: It makes assumptions on the representation 33 * of negative integers and assumes sign-preserving right-shift of negative 34 * signed values. This is a rewrite from scratch that should not suffer from 35 * such issues. 36 * 37 * 2015-12-12, J. Perlinger (perlinger-at-ntp-dot-org) 38 */ 39 int 40 isc_tsmemcmp(const void *p1, const void *p2, size_t nb) { 41 const unsigned char *ucp1 = p1; 42 const unsigned char *ucp2 = p2; 43 unsigned int isLT = 0u; 44 unsigned int isGT = 0u; 45 volatile unsigned int mask = (1u << CHAR_BIT); 46 47 for (/*NOP*/; 0 != nb; --nb, ++ucp1, ++ucp2) { 48 isLT |= mask & 49 ((unsigned int)*ucp1 - (unsigned int)*ucp2); 50 isGT |= mask & 51 ((unsigned int)*ucp2 - (unsigned int)*ucp1); 52 mask &= ~(isLT | isGT); 53 } 54 return (int)(isGT >> CHAR_BIT) - (int)(isLT >> CHAR_BIT); 55 } 56