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
32static __always_inline const char *
33sadd (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. */
39void *
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
86weak_alias (__memchr, memchr)
87libc_hidden_builtin_def (memchr)
88#endif
89

source code of glibc/string/memchr.c