uclibc-ng/libc/string/strstr.c

/* Return the offset of one string within another.
   Copyright (C) 1994, 1996, 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

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

   The GNU C Library 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  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

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;
}