1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
|
/* Copyright (C) 2011-2014 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, see
<http://www.gnu.org/licenses/>. */
#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)
|
