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bfff8b1b | 1 | /* Copyright (C) 2011-2017 Free Software Foundation, Inc. |
63d143a2 CM |
2 | This file is part of the GNU C Library. |
3 | Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011. | |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
ab84e3ff PE |
16 | License along with the GNU C Library. If not, see |
17 | <http://www.gnu.org/licenses/>. */ | |
63d143a2 CM |
18 | |
19 | #include <string.h> | |
20 | #include <stdint.h> | |
21 | ||
22 | char * | |
23 | strrchr (const char *s, int c) | |
24 | { | |
25 | /* Get an aligned pointer. */ | |
26 | const uintptr_t s_int = (uintptr_t) s; | |
27 | const uint32_t *p = (const uint32_t *) (s_int & -4); | |
28 | ||
29 | /* Create four copies of the byte for which we are looking. */ | |
30 | const uint32_t goal = 0x01010101 * (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). Note that this shift count expression works because we | |
36 | know shift counts are taken mod 32. */ | |
37 | const uint32_t before_mask = (1 << (s_int << 3)) - 1; | |
38 | uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib (before_mask, 1)); | |
39 | const char *found = NULL; | |
40 | uint32_t zero_matches, goal_matches; | |
41 | while (1) | |
42 | { | |
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 we found the goal, record the last offset. */ | |
50 | if (__builtin_expect (goal_matches != 0, 0)) | |
51 | { | |
52 | if (__builtin_expect (zero_matches != 0, 0)) | |
53 | { | |
54 | /* Clear any goal after the first zero. */ | |
55 | int first_nul = __insn_ctz (zero_matches); | |
56 | /* The number of top bits we need to clear is | |
57 | 32 - (first_nul + 8). */ | |
58 | int shift_amt = (24 - first_nul); | |
59 | goal_matches <<= shift_amt; | |
60 | goal_matches >>= shift_amt; | |
61 | } | |
62 | if (__builtin_expect (goal_matches != 0, 1)) | |
63 | found = ((char *) p) + 3 - (__insn_clz (goal_matches) >> 3); | |
64 | } | |
65 | ||
66 | if (__builtin_expect (zero_matches != 0, 0)) | |
67 | return (char *) found; | |
68 | ||
69 | v = *++p; | |
70 | } | |
71 | } | |
72 | weak_alias (strrchr, rindex) | |
73 | libc_hidden_builtin_def (strrchr) |