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f18b8dc7d7
Avoid an issue in gcc where some of the vector (aka SIMD) ops will sometimes end up getting wrongly optimized out. We use these instructions in many of the string implementations. If/when we have an upstreamed fix for this problem in gcc we can conditionalize the use of the extended assembly workaround in glibc.
78 lines
2.4 KiB
C
78 lines
2.4 KiB
C
/* Copyright (C) 2011-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
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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 <string.h>
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#include <stdint.h>
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#include "string-endian.h"
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void *
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__memchr (const void *s, int c, size_t n)
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{
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const uint64_t *last_word_ptr;
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const uint64_t *p;
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const char *last_byte_ptr;
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uintptr_t s_int;
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uint64_t goal, before_mask, v, bits;
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char *ret;
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if (__builtin_expect (n == 0, 0))
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{
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/* Don't dereference any memory if the array is empty. */
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return NULL;
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}
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/* Get an aligned pointer. */
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s_int = (uintptr_t) s;
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p = (const uint64_t *) (s_int & -8);
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/* Create eight copies of the byte for which we are looking. */
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goal = copy_byte(c);
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/* Read the first word, but munge it so that bytes before the array
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will not match goal. */
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before_mask = MASK (s_int);
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v = (*p | before_mask) ^ (goal & before_mask);
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/* Compute the address of the last byte. */
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last_byte_ptr = (const char *) s + n - 1;
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/* Handle possible addition overflow. */
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if (__glibc_unlikely ((uintptr_t) last_byte_ptr < (uintptr_t) s))
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last_byte_ptr = (const char *) UINTPTR_MAX;
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/* Compute the address of the word containing the last byte. */
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last_word_ptr = (const uint64_t *) ((uintptr_t) last_byte_ptr & -8);
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while ((bits = v1cmpeq (v, goal)) == 0)
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{
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if (__builtin_expect (p == last_word_ptr, 0))
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{
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/* We already read the last word in the array, so give up. */
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return NULL;
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}
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v = *++p;
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}
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/* We found a match, but it might be in a byte past the end
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of the array. */
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ret = ((char *) p) + (CFZ (bits) >> 3);
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return (ret <= last_byte_ptr) ? ret : NULL;
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}
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weak_alias (__memchr, memchr)
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libc_hidden_builtin_def (memchr)
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