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