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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{
Chris Metcalf3edabee2010-11-24 13:57:42 -050021 const uint32_t *last_word_ptr;
22 const uint32_t *p;
23 const char *last_byte_ptr;
24 uintptr_t s_int;
25 uint32_t goal, before_mask, v, bits;
26 char *ret;
27
28 if (__builtin_expect(n == 0, 0)) {
29 /* Don't dereference any memory if the array is empty. */
30 return NULL;
31 }
32
Chris Metcalf867e3592010-05-28 23:09:12 -040033 /* Get an aligned pointer. */
Chris Metcalf3edabee2010-11-24 13:57:42 -050034 s_int = (uintptr_t) s;
35 p = (const uint32_t *)(s_int & -4);
Chris Metcalf867e3592010-05-28 23:09:12 -040036
37 /* Create four copies of the byte for which we are looking. */
Chris Metcalf3edabee2010-11-24 13:57:42 -050038 goal = 0x01010101 * (uint8_t) c;
Chris Metcalf867e3592010-05-28 23:09:12 -040039
40 /* Read the first word, but munge it so that bytes before the array
41 * will not match goal.
42 *
43 * Note that this shift count expression works because we know
44 * shift counts are taken mod 32.
45 */
Chris Metcalf3edabee2010-11-24 13:57:42 -050046 before_mask = (1 << (s_int << 3)) - 1;
47 v = (*p | before_mask) ^ (goal & before_mask);
Chris Metcalf867e3592010-05-28 23:09:12 -040048
49 /* Compute the address of the last byte. */
Chris Metcalf3edabee2010-11-24 13:57:42 -050050 last_byte_ptr = (const char *)s + n - 1;
Chris Metcalf867e3592010-05-28 23:09:12 -040051
52 /* Compute the address of the word containing the last byte. */
Chris Metcalf3edabee2010-11-24 13:57:42 -050053 last_word_ptr = (const uint32_t *)((uintptr_t) last_byte_ptr & -4);
Chris Metcalf867e3592010-05-28 23:09:12 -040054
55 while ((bits = __insn_seqb(v, goal)) == 0) {
56 if (__builtin_expect(p == last_word_ptr, 0)) {
57 /* We already read the last word in the array,
58 * so give up.
59 */
60 return NULL;
61 }
62 v = *++p;
63 }
64
65 /* We found a match, but it might be in a byte past the end
66 * of the array.
67 */
68 ret = ((char *)p) + (__insn_ctz(bits) >> 3);
69 return (ret <= last_byte_ptr) ? ret : NULL;
70}
71EXPORT_SYMBOL(memchr);