mirror of
git://sourceware.org/git/glibc.git
synced 2024-12-27 04:41:02 +08:00
74 lines
2.4 KiB
C
74 lines
2.4 KiB
C
/* Copyright (C) 2011 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
|
|
|
|
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, write to the Free
|
|
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
|
|
02111-1307 USA. */
|
|
|
|
#include <string.h>
|
|
#include <stdint.h>
|
|
|
|
void *
|
|
__memchr (const void *s, int c, size_t n)
|
|
{
|
|
const uint32_t *last_word_ptr;
|
|
const uint32_t *p;
|
|
const char *last_byte_ptr;
|
|
uintptr_t s_int;
|
|
uint32_t goal, before_mask, v, bits;
|
|
char *ret;
|
|
|
|
if (__builtin_expect (n == 0, 0))
|
|
{
|
|
/* Don't dereference any memory if the array is empty. */
|
|
return NULL;
|
|
}
|
|
|
|
/* Get an aligned pointer. */
|
|
s_int = (uintptr_t) s;
|
|
p = (const uint32_t *) (s_int & -4);
|
|
|
|
/* Create four copies of the byte for which we are looking. */
|
|
goal = 0x01010101 * (uint8_t) c;
|
|
|
|
/* Read the first word, but munge it so that bytes before the array
|
|
will not match goal. Note that this shift count expression works
|
|
because we know shift counts are taken mod 32. */
|
|
before_mask = (1 << (s_int << 3)) - 1;
|
|
v = (*p | before_mask) ^ (goal & before_mask);
|
|
|
|
/* Compute the address of the last byte. */
|
|
last_byte_ptr = (const char *) s + n - 1;
|
|
|
|
/* Compute the address of the word containing the last byte. */
|
|
last_word_ptr = (const uint32_t *) ((uintptr_t) last_byte_ptr & -4);
|
|
|
|
while ((bits = __insn_seqb (v, goal)) == 0)
|
|
{
|
|
if (__builtin_expect (p == last_word_ptr, 0))
|
|
{
|
|
/* We already read the last word in the array, so give up. */
|
|
return NULL;
|
|
}
|
|
v = *++p;
|
|
}
|
|
|
|
/* We found a match, but it might be in a byte past the end of the array. */
|
|
ret = ((char *) p) + (__insn_ctz (bits) >> 3);
|
|
return (ret <= last_byte_ptr) ? ret : NULL;
|
|
}
|
|
weak_alias (__memchr, memchr)
|
|
libc_hidden_builtin_def (memchr)
|