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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 | ||
867e359b CM |
19 | char *strchr(const char *s, int c) |
20 | { | |
21 | int z, g; | |
22 | ||
23 | /* Get an aligned pointer. */ | |
24 | const uintptr_t s_int = (uintptr_t) s; | |
25 | const uint32_t *p = (const uint32_t *)(s_int & -4); | |
26 | ||
27 | /* Create four copies of the byte for which we are looking. */ | |
28 | const uint32_t goal = 0x01010101 * (uint8_t) c; | |
29 | ||
30 | /* Read the first aligned word, but force bytes before the string to | |
31 | * match neither zero nor goal (we make sure the high bit of each | |
32 | * byte is 1, and the low 7 bits are all the opposite of the goal | |
33 | * byte). | |
34 | * | |
35 | * Note that this shift count expression works because we know shift | |
36 | * counts are taken mod 32. | |
37 | */ | |
38 | const uint32_t before_mask = (1 << (s_int << 3)) - 1; | |
39 | uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib(before_mask, 1)); | |
40 | ||
41 | uint32_t zero_matches, goal_matches; | |
42 | while (1) { | |
43 | /* Look for a terminating '\0'. */ | |
44 | zero_matches = __insn_seqb(v, 0); | |
45 | ||
46 | /* Look for the goal byte. */ | |
47 | goal_matches = __insn_seqb(v, goal); | |
48 | ||
49 | if (__builtin_expect(zero_matches | goal_matches, 0)) | |
50 | break; | |
51 | ||
52 | v = *++p; | |
53 | } | |
54 | ||
55 | z = __insn_ctz(zero_matches); | |
56 | g = __insn_ctz(goal_matches); | |
57 | ||
58 | /* If we found c before '\0' we got a match. Note that if c == '\0' | |
59 | * then g == z, and we correctly return the address of the '\0' | |
60 | * rather than NULL. | |
61 | */ | |
62 | return (g <= z) ? ((char *)p) + (g >> 3) : NULL; | |
63 | } | |
64 | EXPORT_SYMBOL(strchr); |