sysdeps/generic/strncmp.c

   1 /* Copyright (C) 1991, 1996 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 Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    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    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <string.h>
  20 #include <memcopy.h>
  21
  22 /* Compare no more than N characters of S1 and S2,
  23    returning less than, equal to or greater than zero
  24    if S1 is lexicographically less than, equal to or
  25    greater than S2.  */
  26 int
  27 strncmp (s1, s2, n)
  28      const char *s1;
  29      const char *s2;
  30      size_t n;
  31 {
  32   unsigned reg_char c1 = '\0';
  33   unsigned reg_char c2 = '\0';
  34
  35   if (n >= 4)
  36     {
  37       size_t n4 = n >> 2;
  38       do
  39         {
  40           c1 = (unsigned char) *s1++;
  41           c2 = (unsigned char) *s2++;
  42           if (c1 == '\0' || c1 != c2)
  43             return c1 - c2;
  44           c1 = (unsigned char) *s1++;
  45           c2 = (unsigned char) *s2++;
  46           if (c1 == '\0' || c1 != c2)
  47             return c1 - c2;
  48           c1 = (unsigned char) *s1++;
  49           c2 = (unsigned char) *s2++;
  50           if (c1 == '\0' || c1 != c2)
  51             return c1 - c2;
  52           c1 = (unsigned char) *s1++;
  53           c2 = (unsigned char) *s2++;
  54           if (c1 == '\0' || c1 != c2)
  55             return c1 - c2;
  56         } while (--n4 > 0);
  57       n &= 3;
  58     }
  59
  60   while (n > 0)
  61     {
  62       c1 = (unsigned char) *s1++;
  63       c2 = (unsigned char) *s2++;
  64       if (c1 == '\0' || c1 != c2)
  65         return c1 - c2;
  66       n--;
  67     }
  68
  69   return c1 - c2;
  70 }