sysdeps/generic/strncmp.c

   1 /* Copyright (C) 1991 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
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <string.h>
  21 #include <memcopy.h>
  22
  23 /* Compare no more than N characters of S1 and S2,
  24    returning less than, equal to or greater than zero
  25    if S1 is lexiographically less than, equal to or
  26    greater than S2.  */
  27 int
  28 DEFUN(strncmp, (s1, s2, n),
  29       CONST char *s1 AND CONST char *s2 AND size_t n)
  30 {
  31   unsigned reg_char c1 = '\0';
  32   unsigned reg_char c2 = '\0';
  33
  34   if (n >= 4)
  35     {
  36       size_t n4 = n >> 2;
  37       do
  38         {
  39           c1 = (unsigned char) *s1++;
  40           c2 = (unsigned char) *s2++;
  41           if (c1 == '\0' || c1 != c2)
  42             return c1 - c2;
  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         } while (--n4 > 0);
  56       n &= 3;
  57     }
  58
  59   while (n > 0)
  60     {
  61       c1 = (unsigned char) *s1++;
  62       c2 = (unsigned char) *s2++;
  63       if (c1 == '\0' || c1 != c2)
  64         return c1 - c2;
  65       n--;
  66     }
  67
  68   return c1 - c2;
  69 }