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Diffstat (limited to 'contrib/ntp/lib/isc/tsmemcmp.c')
-rw-r--r-- | contrib/ntp/lib/isc/tsmemcmp.c | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/contrib/ntp/lib/isc/tsmemcmp.c b/contrib/ntp/lib/isc/tsmemcmp.c new file mode 100644 index 0000000..e6af42e --- /dev/null +++ b/contrib/ntp/lib/isc/tsmemcmp.c @@ -0,0 +1,55 @@ +/* + * 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); +} |