forked from osmocom/wireshark
![Peter Wu](/assets/img/avatar_default.png)
When ASAN is enabled, a false buffer overflow warning is raised. It is a false positive since everything starting at '\0' will get ignored by the PCMPISTRI instruction (see Intel(r) SSE4 Programming Reference, 5.3.1.5 "Valid/Invalid Override of Comparisons", and 5.3.1.2 "Aggregrate Operation", case "Equal any"). Concerns about reading past the end of the page turns out to be false, there always seem to be a valid page after the current one (for static and heap memory at least). It is an non-issue since strlen also does not have issues with this. Rather than fully disabling SSE 4.2 and using the fallback implementation for ASAN-enabled builds, read the set of characters from 'a' into the mask without a 128-bit read and then still use SSE 4.2 for the actual query. Bug: 10214 Change-Id: Ie4a526e60b43bfc08dd1d821556766f14a49be4d Reviewed-on: https://code.wireshark.org/review/2618 Reviewed-by: Peter Wu <peter@lekensteyn.nl> Reviewed-by: Evan Huus <eapache@gmail.com>
232 lines
6.9 KiB
C
232 lines
6.9 KiB
C
/* strcspn with SSE4.2 intrinsics
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Copyright (C) 2009-2014 Free Software Foundation, Inc.
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Contributed by Intel Corporation.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include "config.h"
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#ifdef HAVE_SSE4_2
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#include <glib.h>
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#ifdef WIN32
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#include <tmmintrin.h>
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#include <stdint.h>
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#endif
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#include <nmmintrin.h>
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#include <string.h>
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#include "ws_mempbrk.h"
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/* __has_feature(address_sanitizer) is used later for Clang, this is for
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* compatibility with other compilers (such as GCC and MSVC) */
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#ifndef __has_feature
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# define __has_feature(x) 0
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#endif
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#define cast_128aligned__m128i(p) ((const __m128i *) (const void *) (p))
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/* Helper for variable shifts of SSE registers.
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Copyright (C) 2010 Free Software Foundation, Inc.
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*/
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static const int8_t ___m128i_shift_right[31] =
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{
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
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-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
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};
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static inline __m128i
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__m128i_shift_right (__m128i value, unsigned long int offset)
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{
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/* _mm_loadu_si128() works with unaligned data, cast safe */
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return _mm_shuffle_epi8 (value,
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_mm_loadu_si128 (cast_128aligned__m128i(___m128i_shift_right + offset)));
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}
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/* We use 0x2:
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_SIDD_SBYTE_OPS
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| _SIDD_CMP_EQUAL_ANY
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| _SIDD_POSITIVE_POLARITY
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| _SIDD_LEAST_SIGNIFICANT
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on pcmpistri to compare xmm/mem128
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0 1 2 3 4 5 6 7 8 9 A B C D E F
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X X X X X X X X X X X X X X X X
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against xmm
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0 1 2 3 4 5 6 7 8 9 A B C D E F
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A A A A A A A A A A A A A A A A
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to find out if the first 16byte data element has any byte A and
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the offset of the first byte. There are 3 cases:
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1. The first 16byte data element has the byte A at the offset X.
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2. The first 16byte data element has EOS and doesn't have the byte A.
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3. The first 16byte data element is valid and doesn't have the byte A.
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Here is the table of ECX, CFlag, ZFlag and SFlag for 2 cases:
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1 X 1 0/1 0
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2 16 0 1 0
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3 16 0 0 0
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We exit from the loop for cases 1 and 2 with jbe which branches
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when either CFlag or ZFlag is 1. If CFlag == 1, ECX has the offset
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X for case 1. */
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const char *
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_ws_mempbrk_sse42(const char *s, size_t slen, const char *a)
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{
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const char *aligned;
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__m128i mask;
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int offset;
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#if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
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{
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/* As 'a' is not guarantueed to have a size of at least 16 bytes, and is not
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* aligned, _mm_load_si128() cannot be used when ASAN is enabled. That
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* triggers a buffer overflow which is harmless as 'a' is guaranteed to be
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* '\0' terminated, and the PCMISTRI instruction always ignored everything
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* starting from EOS ('\0'). A false positive indeed. */
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size_t length;
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length = strlen(a);
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/* Don't use SSE4.2 if the length of A > 16. */
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if (length > 16)
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return _ws_mempbrk(s, slen, a);
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mask = _mm_setzero_si128();
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memcpy(&mask, a, length);
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}
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#else /* else if ASAN is disabled */
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offset = (int) ((size_t) a & 15);
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aligned = (const char *) ((size_t) a & -16L);
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if (offset != 0)
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{
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int length;
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/* Load masks. */
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/* cast safe - _mm_load_si128() it's 16B aligned */
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mask = __m128i_shift_right(_mm_load_si128 (cast_128aligned__m128i(aligned)), offset);
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/* Find where the NULL terminator is. */
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length = _mm_cmpistri (mask, mask, 0x3a);
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if (length == 16 - offset)
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{
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/* There is no NULL terminator. */
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__m128i mask1 = _mm_load_si128 (cast_128aligned__m128i(aligned + 16));
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int idx = _mm_cmpistri (mask1, mask1, 0x3a);
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length += idx;
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/* Don't use SSE4.2 if the length of A > 16. */
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if (length > 16)
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return _ws_mempbrk(s, slen, a);
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if (idx != 0)
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{
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/* Combine mask0 and mask1. We could play games with
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palignr, but frankly this data should be in L1 now
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so do the merge via an unaligned load. */
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mask = _mm_loadu_si128 (cast_128aligned__m128i(a));
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}
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}
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}
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else
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{
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int length;
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/* A is aligned. (cast safe) */
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mask = _mm_load_si128 (cast_128aligned__m128i(a));
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/* Find where the NULL terminator is. */
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length = _mm_cmpistri (mask, mask, 0x3a);
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if (length == 16)
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{
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/* There is no NULL terminator. Don't use SSE4.2 if the length
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of A > 16. */
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if (a[16] != 0)
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return _ws_mempbrk(s, slen, a);
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}
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}
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#endif /* ASAN disabled */
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offset = (int) ((size_t) s & 15);
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aligned = (const char *) ((size_t) s & -16L);
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if (offset != 0)
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{
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/* Check partial string. cast safe it's 16B aligned */
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__m128i value = __m128i_shift_right (_mm_load_si128 (cast_128aligned__m128i(aligned)), offset);
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int length = _mm_cmpistri (mask, value, 0x2);
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/* No need to check ZFlag since ZFlag is always 1. */
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int cflag = _mm_cmpistrc (mask, value, 0x2);
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int idx = _mm_cmpistri (value, value, 0x3a);
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if (cflag)
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return s + length;
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/* Find where the NULL terminator is. */
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if (idx < 16 - offset)
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{
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/* fond NUL @ 'idx', need to switch to slower mempbrk */
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return _ws_mempbrk(s + idx + 1, slen - idx - 1, a); /* slen is bigger than 16 & idx < 16 so no undeflow here */
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}
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aligned += 16;
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slen -= (16 - offset);
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}
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else
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aligned = s;
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while (slen >= 16)
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{
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__m128i value = _mm_load_si128 (cast_128aligned__m128i(aligned));
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int idx = _mm_cmpistri (mask, value, 0x2);
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int cflag = _mm_cmpistrc (mask, value, 0x2);
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int zflag = _mm_cmpistrz (mask, value, 0x2);
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if (cflag)
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return aligned + idx;
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if (zflag)
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{
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/* found NUL, need to switch to slower mempbrk */
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return _ws_mempbrk(aligned, slen, a);
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}
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aligned += 16;
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slen -= 16;
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}
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/* XXX, use mempbrk_slow here? */
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return _ws_mempbrk(aligned, slen, a);
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}
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#endif /* HAVE_SSE4_2 */
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/*
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* Editor modelines
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*
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* Local Variables:
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* c-basic-offset: 2
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* tab-width: 8
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* indent-tabs-mode: nil
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* End:
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*
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* ex: set shiftwidth=2 tabstop=8 expandtab:
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* :indentSize=2:tabSize=8:noTabs=true:
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*/
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