blob: 6235283b4859e031b22d5a168ef611fc0b4368c8 [file] [log] [blame]
Chris Metcalf867e3592010-05-28 23:09:12 -04001/*
2 * Copyright 2010 Tilera Corporation. All Rights Reserved.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation, version 2.
7 *
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11 * NON INFRINGEMENT. See the GNU General Public License for
12 * more details.
13 */
14
15#include <linux/types.h>
16#include <linux/string.h>
17#include <linux/module.h>
18
19void *memchr(const void *s, int c, size_t n)
20{
21 /* Get an aligned pointer. */
22 const uintptr_t s_int = (uintptr_t) s;
23 const uint32_t *p = (const uint32_t *)(s_int & -4);
24
25 /* Create four copies of the byte for which we are looking. */
26 const uint32_t goal = 0x01010101 * (uint8_t) c;
27
28 /* Read the first word, but munge it so that bytes before the array
29 * will not match goal.
30 *
31 * Note that this shift count expression works because we know
32 * shift counts are taken mod 32.
33 */
34 const uint32_t before_mask = (1 << (s_int << 3)) - 1;
35 uint32_t v = (*p | before_mask) ^ (goal & before_mask);
36
37 /* Compute the address of the last byte. */
38 const char *const last_byte_ptr = (const char *)s + n - 1;
39
40 /* Compute the address of the word containing the last byte. */
41 const uint32_t *const last_word_ptr =
42 (const uint32_t *)((uintptr_t) last_byte_ptr & -4);
43
44 uint32_t bits;
45 char *ret;
46
47 if (__builtin_expect(n == 0, 0)) {
48 /* Don't dereference any memory if the array is empty. */
49 return NULL;
50 }
51
52 while ((bits = __insn_seqb(v, goal)) == 0) {
53 if (__builtin_expect(p == last_word_ptr, 0)) {
54 /* We already read the last word in the array,
55 * so give up.
56 */
57 return NULL;
58 }
59 v = *++p;
60 }
61
62 /* We found a match, but it might be in a byte past the end
63 * of the array.
64 */
65 ret = ((char *)p) + (__insn_ctz(bits) >> 3);
66 return (ret <= last_byte_ptr) ? ret : NULL;
67}
68EXPORT_SYMBOL(memchr);