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/* memrchr -- find the last occurrence of a byte in a memory block
Copyright (C) 1991-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <string-fzb.h>
#include <string-fzc.h>
#include <string-fzi.h>
#include <string-shift.h>
#include <string.h>
#include <libc-pointer-arith.h>
#undef __memrchr
#undef memrchr
#ifdef MEMRCHR
# define __memrchr MEMRCHR
#endif
void *
__memrchr (const void *s, int c_in, size_t n)
{
if (__glibc_unlikely (n == 0))
return NULL;
const op_t *word_ptr = (const op_t *) PTR_ALIGN_UP (s + n, sizeof (op_t));
uintptr_t s_int = (uintptr_t) s + n;
op_t word = *--word_ptr;
op_t repeated_c = repeat_bytes (c_in);
/* Compute the address of the word containing the initial byte. */
const op_t *sword = (const op_t *) PTR_ALIGN_DOWN (s, sizeof (op_t));
/* If the end of buffer is not op_t aligned, mask off the undesirable bits
before find the last byte position. */
find_t mask = shift_find_last (find_eq_all (word, repeated_c), s_int);
if (mask != 0)
{
char *ret = (char *) word_ptr + index_last (mask);
return ret >= (char *) s ? ret : NULL;
}
if (word_ptr == sword)
return NULL;
word = *--word_ptr;
while (word_ptr != sword)
{
if (has_eq (word, repeated_c))
return (char *) word_ptr + index_last_eq (word, repeated_c);
word = *--word_ptr;
}
if (has_eq (word, repeated_c))
{
/* We found a match, but it might be in a byte past the end of the
array. */
char *ret = (char *) word_ptr + index_last_eq (word, repeated_c);
if (ret >= (char *) s)
return ret;
}
return NULL;
}
#ifndef MEMRCHR
libc_hidden_def (__memrchr)
weak_alias (__memrchr, memrchr)
#endif
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