128 lines
2.9 KiB
C
128 lines
2.9 KiB
C
/* Return the offset of one string within another.
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Copyright (C) 1994, 1996, 1997, 2000 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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/*
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* My personal strstr() implementation that beats most other algorithms.
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* Until someone tells me otherwise, I assume that this is the
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* fastest implementation of strstr() in C.
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* I deliberately chose not to comment it. You should have at least
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* as much fun trying to understand it, as I had to write it :-).
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*
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* Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
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#if HAVE_CONFIG_H
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# include <config.h>
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#endif
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#if defined _LIBC || defined HAVE_STRING_H
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# include <string.h>
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#endif
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typedef unsigned chartype;
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#undef strstr
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char *
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strstr (phaystack, pneedle)
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const char *phaystack;
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const char *pneedle;
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{
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register const unsigned char *haystack, *needle;
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register chartype b, c;
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haystack = (const unsigned char *) phaystack;
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needle = (const unsigned char *) pneedle;
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b = *needle;
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if (b != '\0')
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{
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haystack--; /* possible ANSI violation */
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do
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{
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c = *++haystack;
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if (c == '\0')
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goto ret0;
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}
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while (c != b);
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c = *++needle;
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if (c == '\0')
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goto foundneedle;
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++needle;
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goto jin;
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for (;;)
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{
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register chartype a;
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register const unsigned char *rhaystack, *rneedle;
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do
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{
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a = *++haystack;
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if (a == '\0')
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goto ret0;
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if (a == b)
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break;
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a = *++haystack;
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if (a == '\0')
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goto ret0;
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shloop:
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;
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}
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while (a != b);
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jin: a = *++haystack;
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if (a == '\0')
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goto ret0;
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if (a != c)
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goto shloop;
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rhaystack = haystack-- + 1;
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rneedle = needle;
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a = *rneedle;
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if (*rhaystack == a)
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do
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{
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if (a == '\0')
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goto foundneedle;
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++rhaystack;
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a = *++needle;
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if (*rhaystack != a)
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break;
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if (a == '\0')
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goto foundneedle;
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++rhaystack;
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a = *++needle;
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}
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while (*rhaystack == a);
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needle = rneedle; /* took the register-poor approach */
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if (a == '\0')
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break;
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}
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}
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foundneedle:
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return (char*) haystack;
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ret0:
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return 0;
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}
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