string/strncmp.c

   1 /* Copyright (C) 1991, 1996, 1997, 2003 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <string.h>
  20 #include <memcopy.h>
  21
  22 #undef strncmp
  23
  24 #ifndef STRNCMP
  25 #define STRNCMP strncmp
  26 #endif
  27
  28 /* Compare no more than N characters of S1 and S2,
  29    returning less than, equal to or greater than zero
  30    if S1 is lexicographically less than, equal to or
  31    greater than S2.  */
  32 int
  33 STRNCMP (const char *s1, const char *s2, size_t n)
  34 {
  35   unsigned reg_char c1 = '\0';
  36   unsigned reg_char c2 = '\0';
  37
  38   if (n >= 4)
  39     {
  40       size_t n4 = n >> 2;
  41       do
  42         {
  43           c1 = (unsigned char) *s1++;
  44           c2 = (unsigned char) *s2++;
  45           if (c1 == '\0' || c1 != c2)
  46             return c1 - c2;
  47           c1 = (unsigned char) *s1++;
  48           c2 = (unsigned char) *s2++;
  49           if (c1 == '\0' || c1 != c2)
  50             return c1 - c2;
  51           c1 = (unsigned char) *s1++;
  52           c2 = (unsigned char) *s2++;
  53           if (c1 == '\0' || c1 != c2)
  54             return c1 - c2;
  55           c1 = (unsigned char) *s1++;
  56           c2 = (unsigned char) *s2++;
  57           if (c1 == '\0' || c1 != c2)
  58             return c1 - c2;
  59         } while (--n4 > 0);
  60       n &= 3;
  61     }
  62
  63   while (n > 0)
  64     {
  65       c1 = (unsigned char) *s1++;
  66       c2 = (unsigned char) *s2++;
  67       if (c1 == '\0' || c1 != c2)
  68         return c1 - c2;
  69       n--;
  70     }
  71
  72   return c1 - c2;
  73 }
  74
  75 libc_hidden_builtin_def (STRNCMP)