1/* Copyright (C) 1991-2022 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18#include <string.h>
19#include <memcopy.h>
20
21#undef strncmp
22
23#ifndef STRNCMP
24#define STRNCMP strncmp
25#endif
26
27/* Compare no more than N characters of S1 and S2,
28 returning less than, equal to or greater than zero
29 if S1 is lexicographically less than, equal to or
30 greater than S2. */
31int
32STRNCMP (const char *s1, const char *s2, size_t n)
33{
34 unsigned char c1 = '\0';
35 unsigned char c2 = '\0';
36
37 if (n >= 4)
38 {
39 size_t n4 = n >> 2;
40 do
41 {
42 c1 = (unsigned char) *s1++;
43 c2 = (unsigned char) *s2++;
44 if (c1 == '\0' || c1 != c2)
45 return c1 - c2;
46 c1 = (unsigned char) *s1++;
47 c2 = (unsigned char) *s2++;
48 if (c1 == '\0' || c1 != c2)
49 return c1 - c2;
50 c1 = (unsigned char) *s1++;
51 c2 = (unsigned char) *s2++;
52 if (c1 == '\0' || c1 != c2)
53 return c1 - c2;
54 c1 = (unsigned char) *s1++;
55 c2 = (unsigned char) *s2++;
56 if (c1 == '\0' || c1 != c2)
57 return c1 - c2;
58 } while (--n4 > 0);
59 n &= 3;
60 }
61
62 while (n > 0)
63 {
64 c1 = (unsigned char) *s1++;
65 c2 = (unsigned char) *s2++;
66 if (c1 == '\0' || c1 != c2)
67 return c1 - c2;
68 n--;
69 }
70
71 return c1 - c2;
72}
73
74libc_hidden_builtin_def (STRNCMP)
75

source code of glibc/string/strncmp.c