1 | /* memrchr -- find the last occurrence of a byte in a memory block |
2 | Copyright (C) 1991-2024 Free Software Foundation, Inc. |
3 | This file is part of the GNU C Library. |
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 |
16 | License along with the GNU C Library; if not, see |
17 | <https://www.gnu.org/licenses/>. */ |
18 | |
19 | #include <string-fzb.h> |
20 | #include <string-fzc.h> |
21 | #include <string-fzi.h> |
22 | #include <string-shift.h> |
23 | #include <string.h> |
24 | #include <libc-pointer-arith.h> |
25 | |
26 | #undef __memrchr |
27 | #undef memrchr |
28 | |
29 | #ifdef MEMRCHR |
30 | # define __memrchr MEMRCHR |
31 | #endif |
32 | |
33 | void * |
34 | __memrchr (const void *s, int c_in, size_t n) |
35 | { |
36 | if (__glibc_unlikely (n == 0)) |
37 | return NULL; |
38 | |
39 | const op_t *word_ptr = (const op_t *) PTR_ALIGN_UP (s + n, sizeof (op_t)); |
40 | uintptr_t s_int = (uintptr_t) s + n; |
41 | |
42 | op_t word = *--word_ptr; |
43 | op_t repeated_c = repeat_bytes (c_in); |
44 | |
45 | /* Compute the address of the word containing the initial byte. */ |
46 | const op_t *sword = (const op_t *) PTR_ALIGN_DOWN (s, sizeof (op_t)); |
47 | |
48 | /* If the end of buffer is not op_t aligned, mask off the undesirable bits |
49 | before find the last byte position. */ |
50 | find_t mask = shift_find_last (word: find_eq_all (x1: word, x2: repeated_c), s: s_int); |
51 | if (mask != 0) |
52 | { |
53 | char *ret = (char *) word_ptr + index_last (c: mask); |
54 | return ret >= (char *) s ? ret : NULL; |
55 | } |
56 | if (word_ptr == sword) |
57 | return NULL; |
58 | word = *--word_ptr; |
59 | |
60 | while (word_ptr != sword) |
61 | { |
62 | if (has_eq (x1: word, x2: repeated_c)) |
63 | return (char *) word_ptr + index_last_eq (x1: word, x2: repeated_c); |
64 | word = *--word_ptr; |
65 | } |
66 | |
67 | if (has_eq (x1: word, x2: repeated_c)) |
68 | { |
69 | /* We found a match, but it might be in a byte past the end of the |
70 | array. */ |
71 | char *ret = (char *) word_ptr + index_last_eq (x1: word, x2: repeated_c); |
72 | if (ret >= (char *) s) |
73 | return ret; |
74 | } |
75 | return NULL; |
76 | } |
77 | #ifndef MEMRCHR |
78 | libc_hidden_def (__memrchr) |
79 | weak_alias (__memrchr, memrchr) |
80 | #endif |
81 | |