1 | /* Scan memory for a character. Generic version |
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 <libc-pointer-arith.h> |
20 | #include <string-fzb.h> |
21 | #include <string-fzc.h> |
22 | #include <string-fzi.h> |
23 | #include <string-shift.h> |
24 | #include <string.h> |
25 | |
26 | #undef memchr |
27 | |
28 | #ifdef MEMCHR |
29 | # define __memchr MEMCHR |
30 | #endif |
31 | |
32 | static __always_inline const char * |
33 | sadd (uintptr_t x, uintptr_t y) |
34 | { |
35 | return (const char *)(y > UINTPTR_MAX - x ? UINTPTR_MAX : x + y); |
36 | } |
37 | |
38 | /* Search no more than N bytes of S for C. */ |
39 | void * |
40 | __memchr (void const *s, int c_in, size_t n) |
41 | { |
42 | if (__glibc_unlikely (n == 0)) |
43 | return NULL; |
44 | |
45 | /* Read the first word, but munge it so that bytes before the array |
46 | will not match goal. */ |
47 | const op_t *word_ptr = PTR_ALIGN_DOWN (s, sizeof (op_t)); |
48 | uintptr_t s_int = (uintptr_t) s; |
49 | |
50 | op_t word = *word_ptr; |
51 | op_t repeated_c = repeat_bytes (c_in); |
52 | /* Compute the address of the last byte taking in consideration possible |
53 | overflow. */ |
54 | const char *lbyte = sadd (x: s_int, y: n - 1); |
55 | /* And also the address of the word containing the last byte. */ |
56 | const op_t *lword = (const op_t *) PTR_ALIGN_DOWN (lbyte, sizeof (op_t)); |
57 | |
58 | find_t mask = shift_find (word: find_eq_all (x1: word, x2: repeated_c), s: s_int); |
59 | if (mask != 0) |
60 | { |
61 | char *ret = (char *) s + index_first (c: mask); |
62 | return (ret <= lbyte) ? ret : NULL; |
63 | } |
64 | if (word_ptr == lword) |
65 | return NULL; |
66 | |
67 | word = *++word_ptr; |
68 | while (word_ptr != lword) |
69 | { |
70 | if (has_eq (x1: word, x2: repeated_c)) |
71 | return (char *) word_ptr + index_first_eq (x1: word, x2: repeated_c); |
72 | word = *++word_ptr; |
73 | } |
74 | |
75 | if (has_eq (x1: word, x2: repeated_c)) |
76 | { |
77 | /* We found a match, but it might be in a byte past the end of the |
78 | array. */ |
79 | char *ret = (char *) word_ptr + index_first_eq (x1: word, x2: repeated_c); |
80 | if (ret <= lbyte) |
81 | return ret; |
82 | } |
83 | return NULL; |
84 | } |
85 | #ifndef MEMCHR |
86 | weak_alias (__memchr, memchr) |
87 | libc_hidden_builtin_def (memchr) |
88 | #endif |
89 | |