sys/libkern/strstr.c

   1 /*
   2  * Copyright (c) 2014 The DragonFly Project.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  *
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in
  12  *    the documentation and/or other materials provided with the
  13  *    distribution.
  14  * 3. Neither the name of The DragonFly Project nor the names of its
  15  *    contributors may be used to endorse or promote products derived
  16  *    from this software without specific, prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  19  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  21  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  22  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  23  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  24  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  25  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  26  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  27  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  28  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  */
  31
  32 #include <sys/libkern.h>
  33
  34 char *
  35 strstr(const char *s, const char *find)
  36 {
  37         char c, sc;
  38         size_t len;
  39
  40         if ((c = *find++) != 0) {
  41                 len = strlen(find);
  42                 do {
  43                         do {
  44                                 if ((sc = *s++) == 0)
  45                                         return (NULL);
  46                         } while (sc != c);
  47                 } while (strncmp(s, find, len) != 0);
  48                 s--;
  49         }
  50         return (__DECONST(char *, s));
  51 }