string/strncmp.c

   1 /* Copyright (C) 1991-2020 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.  */
  31 int
  32 STRNCMP (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
  74 libc_hidden_builtin_def (STRNCMP)