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 #undef strchr
20
strchr(const char * s,int c)21 char *strchr(const char *s, int c)
22 {
23 int z, g;
24
25 /* Get an aligned pointer. */
26 const uintptr_t s_int = (uintptr_t) s;
27 const uint64_t *p = (const uint64_t *)(s_int & -8);
28
29 /* Create eight copies of the byte for which we are looking. */
30 const uint64_t goal = 0x0101010101010101ULL * (uint8_t) c;
31
32 /* Read the first aligned word, but force bytes before the string to
33 * match neither zero nor goal (we make sure the high bit of each
34 * byte is 1, and the low 7 bits are all the opposite of the goal
35 * byte).
36 *
37 * Note that this shift count expression works because we know shift
38 * counts are taken mod 64.
39 */
40 const uint64_t before_mask = (1ULL << (s_int << 3)) - 1;
41 uint64_t v = (*p | before_mask) ^
42 (goal & __insn_v1shrsi(before_mask, 1));
43
44 uint64_t zero_matches, goal_matches;
45 while (1) {
46 /* Look for a terminating '\0'. */
47 zero_matches = __insn_v1cmpeqi(v, 0);
48
49 /* Look for the goal byte. */
50 goal_matches = __insn_v1cmpeq(v, goal);
51
52 if (__builtin_expect((zero_matches | goal_matches) != 0, 0))
53 break;
54
55 v = *++p;
56 }
57
58 z = __insn_ctz(zero_matches);
59 g = __insn_ctz(goal_matches);
60
61 /* If we found c before '\0' we got a match. Note that if c == '\0'
62 * then g == z, and we correctly return the address of the '\0'
63 * rather than NULL.
64 */
65 return (g <= z) ? ((char *)p) + (g >> 3) : NULL;
66 }
67 EXPORT_SYMBOL(strchr);
68