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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.
68 lines
2.2 KiB
C
68 lines
2.2 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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#undef strchr
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char *
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strchr (const char *s, int c)
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{
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int z, g;
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/* Get an aligned pointer. */
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const uintptr_t s_int = (uintptr_t) s;
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const uint64_t *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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const uint64_t goal = copy_byte(c);
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/* Read the first aligned word, but force bytes before the string to
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match neither zero nor goal (we make sure the high bit of each byte
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is 1, and the low 7 bits are all the opposite of the goal byte). */
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const uint64_t before_mask = MASK (s_int);
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uint64_t v = (*p | before_mask) ^ (goal & v1shrui (before_mask, 1));
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uint64_t zero_matches, goal_matches;
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while (1)
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{
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/* Look for a terminating '\0'. */
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zero_matches = v1cmpeqi (v, 0);
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/* Look for the goal byte. */
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goal_matches = v1cmpeq (v, goal);
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if (__builtin_expect ((zero_matches | goal_matches) != 0, 0))
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break;
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v = *++p;
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}
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z = CFZ (zero_matches);
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g = CFZ (goal_matches);
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/* If we found c before '\0' we got a match. Note that if c == '\0'
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then g == z, and we correctly return the address of the '\0'
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rather than NULL. */
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return (g <= z) ? ((char *) p) + (g >> 3) : NULL;
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}
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weak_alias (strchr, index)
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libc_hidden_builtin_def (strchr)
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