/* $NetBSD: tsmemcmp.c,v 1.3 2020/05/25 20:47:20 christos Exp $ */ /* * Copyright (C) 2004-2007, 2011, 2012 Internet Systems Consortium, Inc. ("ISC") * Copyright (C) 1999-2001, 2003 Internet Software Consortium. * * Permission to use, copy, modify, and/or distribute this software for any * purpose with or without fee is hereby granted, provided that the above * copyright notice and this permission notice appear in all copies. * * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY * AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR * PERFORMANCE OF THIS SOFTWARE. */ /* Id */ /*! \file */ #include <config.h> #include <limits.h> #include <isc/string.h> /* Making a portable memcmp that has no internal branches and loops always * once for every byte without early-out shortcut has a few challenges. * * Inspired by 'timingsafe_memcmp()' from the BSD system and * https://github.com/libressl-portable/openbsd/blob/master/src/lib/libc/string/timingsafe_memcmp.c * * Sadly, that one is not portable C: It makes assumptions on the representation * of negative integers and assumes sign-preserving right-shift of negative * signed values. This is a rewrite from scratch that should not suffer from * such issues. * * 2015-12-12, J. Perlinger (perlinger-at-ntp-dot-org) */ int isc_tsmemcmp(const void *p1, const void *p2, size_t nb) { const unsigned char *ucp1 = p1; const unsigned char *ucp2 = p2; unsigned int isLT = 0u; unsigned int isGT = 0u; volatile unsigned int mask = (1u << CHAR_BIT); for (/*NOP*/; 0 != nb; --nb, ++ucp1, ++ucp2) { isLT |= mask & ((unsigned int)*ucp1 - (unsigned int)*ucp2); isGT |= mask & ((unsigned int)*ucp2 - (unsigned int)*ucp1); mask &= ~(isLT | isGT); } return (int)(isGT >> CHAR_BIT) - (int)(isLT >> CHAR_BIT); } |