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74 lines
2.7 KiB
C
74 lines
2.7 KiB
C
/* Copyright (C) 2011-2015 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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char *
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strrchr (const char *s, int c)
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{
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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 uint32_t *p = (const uint32_t *) (s_int & -4);
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/* Create four copies of the byte for which we are looking. */
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const uint32_t goal = 0x01010101 * (uint8_t) 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
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byte is 1, and the low 7 bits are all the opposite of the goal
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byte). Note that this shift count expression works because we
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know shift counts are taken mod 32. */
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const uint32_t before_mask = (1 << (s_int << 3)) - 1;
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uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib (before_mask, 1));
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const char *found = NULL;
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uint32_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 = __insn_seqb (v, 0);
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/* Look for the goal byte. */
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goal_matches = __insn_seqb (v, goal);
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/* If we found the goal, record the last offset. */
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if (__builtin_expect (goal_matches != 0, 0))
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{
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if (__builtin_expect (zero_matches != 0, 0))
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{
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/* Clear any goal after the first zero. */
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int first_nul = __insn_ctz (zero_matches);
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/* The number of top bits we need to clear is
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32 - (first_nul + 8). */
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int shift_amt = (24 - first_nul);
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goal_matches <<= shift_amt;
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goal_matches >>= shift_amt;
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}
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if (__builtin_expect (goal_matches != 0, 1))
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found = ((char *) p) + 3 - (__insn_clz (goal_matches) >> 3);
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}
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if (__builtin_expect (zero_matches != 0, 0))
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return (char *) found;
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v = *++p;
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}
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}
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weak_alias (strrchr, rindex)
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libc_hidden_builtin_def (strrchr)
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