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
strchr(const char * s,int c)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);
65