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867e359b CM |
1 | /* |
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 | ||
19 | void *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 | } | |
68 | EXPORT_SYMBOL(memchr); |