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81 lines
2.4 KiB
C
81 lines
2.4 KiB
C
/* memrchr -- find the last occurrence of a byte in a memory block
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Copyright (C) 1991-2025 Free Software Foundation, Inc.
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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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<https://www.gnu.org/licenses/>. */
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#include <string-fzb.h>
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#include <string-fzc.h>
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#include <string-fzi.h>
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#include <string-shift.h>
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#include <string.h>
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#include <libc-pointer-arith.h>
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#undef __memrchr
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#undef memrchr
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#ifdef MEMRCHR
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# define __memrchr MEMRCHR
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#endif
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void *
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__memrchr (const void *s, int c_in, size_t n)
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{
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if (__glibc_unlikely (n == 0))
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return NULL;
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const op_t *word_ptr = (const op_t *) PTR_ALIGN_UP (s + n, sizeof (op_t));
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uintptr_t s_int = (uintptr_t) s + n;
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op_t word = *--word_ptr;
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op_t repeated_c = repeat_bytes (c_in);
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/* Compute the address of the word containing the initial byte. */
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const op_t *sword = (const op_t *) PTR_ALIGN_DOWN (s, sizeof (op_t));
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/* If the end of buffer is not op_t aligned, mask off the undesirable bits
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before find the last byte position. */
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find_t mask = shift_find_last (find_eq_all (word, repeated_c), s_int);
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if (mask != 0)
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{
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char *ret = (char *) word_ptr + index_last (mask);
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return ret >= (char *) s ? ret : NULL;
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}
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if (word_ptr == sword)
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return NULL;
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word = *--word_ptr;
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while (word_ptr != sword)
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{
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if (has_eq (word, repeated_c))
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return (char *) word_ptr + index_last_eq (word, repeated_c);
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word = *--word_ptr;
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}
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if (has_eq (word, repeated_c))
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{
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/* We found a match, but it might be in a byte past the end of the
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array. */
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char *ret = (char *) word_ptr + index_last_eq (word, repeated_c);
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if (ret >= (char *) s)
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return ret;
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}
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return NULL;
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}
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#ifndef MEMRCHR
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libc_hidden_def (__memrchr)
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weak_alias (__memrchr, memrchr)
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#endif
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