common/lib/libc/string/strncmp.c

   1 /*      $NetBSD: strncmp.c,v 1.2 2007/06/04 18:19:27 christos Exp $     */
   2
   3 /*
   4  * Copyright (c) 1989, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  */
  31
  32 #include <sys/cdefs.h>
  33 #if defined(LIBC_SCCS) && !defined(lint)
  34 #if 0
  35 static char sccsid[] = "@(#)strncmp.c   8.1 (Berkeley) 6/4/93";
  36 #else
  37 __RCSID("$NetBSD: strncmp.c,v 1.2 2007/06/04 18:19:27 christos Exp $");
  38 #endif
  39 #endif /* LIBC_SCCS and not lint */
  40
  41 #if !defined(_KERNEL) && !defined(_STANDALONE)
  42 #include <assert.h>
  43 #include <string.h>
  44 #else
  45 #include <lib/libkern/libkern.h>
  46 #endif
  47
  48 int
  49 strncmp(const char *s1, const char *s2, size_t n)
  50 {
  51
  52         _DIAGASSERT(s1 != NULL);
  53         _DIAGASSERT(s2 != NULL);
  54
  55         if (n == 0)
  56                 return (0);
  57         do {
  58                 if (*s1 != *s2++)
  59                         return (*(const unsigned char *)s1 -
  60                             *(const unsigned char *)--s2);
  61                 if (*s1++ == 0)
  62                         break;
  63         } while (--n != 0);
  64         return (0);
  65 }