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18aecc2b CM |
1 | /* |
2 | * Copyright 2011 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 | const uint64_t *last_word_ptr; | |
22 | const uint64_t *p; | |
23 | const char *last_byte_ptr; | |
24 | uintptr_t s_int; | |
25 | uint64_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 | ||
33 | /* Get an aligned pointer. */ | |
34 | s_int = (uintptr_t) s; | |
35 | p = (const uint64_t *)(s_int & -8); | |
36 | ||
37 | /* Create eight copies of the byte for which we are looking. */ | |
38 | goal = 0x0101010101010101ULL * (uint8_t) c; | |
39 | ||
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 64. | |
45 | */ | |
46 | before_mask = (1ULL << (s_int << 3)) - 1; | |
47 | v = (*p | before_mask) ^ (goal & before_mask); | |
48 | ||
49 | /* Compute the address of the last byte. */ | |
50 | last_byte_ptr = (const char *)s + n - 1; | |
51 | ||
52 | /* Compute the address of the word containing the last byte. */ | |
53 | last_word_ptr = (const uint64_t *)((uintptr_t) last_byte_ptr & -8); | |
54 | ||
55 | while ((bits = __insn_v1cmpeq(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 | } | |
71 | EXPORT_SYMBOL(memchr); |