source: vendor/bash/3.1-p17/lib/sh/strstr.c

/* Copyright (C) 1994, 1999 Free Software Foundation, Inc.
This file is part of the GNU C Library.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/*
 * My personal strstr() implementation that beats most other algorithms.
 * Until someone tells me otherwise, I assume that this is the
 * fastest implementation of strstr() in C.
 * I deliberately chose not to comment it.  You should have at least
 * as much fun trying to understand it, as I had to write it :-).
 *
 * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#if defined _LIBC || defined HAVE_STRING_H
# include <string.h>
#endif
#include <sys/types.h>

typedef unsigned chartype;

#undef strstr

char *
strstr (const char *phaystack, const char *pneedle)
{
  register const unsigned char *haystack, *needle;
  register chartype b, c;

  haystack = (const unsigned char *) phaystack;
  needle = (const unsigned char *) pneedle;

  b = *needle;
  if (b != '\0')
    {
      haystack--;                               /* possible ANSI violation */
      do
        {
          c = *++haystack;
          if (c == '\0')
            goto ret0;
        }
      while (c != b);

      c = *++needle;
      if (c == '\0')
        goto foundneedle;
      ++needle;
      goto jin;

      for (;;)
        {
          register chartype a;
          register const unsigned char *rhaystack, *rneedle;

          do
            {
              a = *++haystack;
              if (a == '\0')
                goto ret0;
              if (a == b)
                break;
              a = *++haystack;
              if (a == '\0')
                goto ret0;
shloop:;    }
          while (a != b);

jin:      a = *++haystack;
          if (a == '\0')
            goto ret0;

          if (a != c)
            goto shloop;

          rhaystack = haystack-- + 1;
          rneedle = needle;
          a = *rneedle;

          if (*rhaystack == a)
            do
              {
                if (a == '\0')
                  goto foundneedle;
                ++rhaystack;
                a = *++needle;
                if (*rhaystack != a)
                  break;
                if (a == '\0')
                  goto foundneedle;
                ++rhaystack;
                a = *++needle;
              }
            while (*rhaystack == a);

          needle = rneedle;                /* took the register-poor approach */

          if (a == '\0')
            break;
        }
    }
foundneedle:
  return (char*) haystack;
ret0:
  return 0;
}