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From Ilya Dogolazky ilya.dogolazky at teleca dot fi: 

The new algorithm does not use any array initialisation.
Instead of that the only integer variable "index" is initialized.
It is not using any bitwise operations and shifts as well.

The well-known algorithm (an efficient representation for sparse sets) is
mentioned as exercise 2.12 in "The Design and Analysis of Computer Algorithms"
by Alfred Aho, John Hopcroft and Jeffrey Ullman. It is described here
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.30.7319
and here
http://research.swtch.com/2008/03/using-uninitialized-memory-for-fun-and.html
This commit is contained in:
christos 2008-09-24 14:36:02 +00:00
parent 84b55d4784
commit 194e105784
1 changed files with 22 additions and 7 deletions
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29
lib/libc/string/strpbrk.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: strpbrk.c,v 1.16 2008/02/23 15:18:04 christos Exp $ */
/* $NetBSD: strpbrk.c,v 1.17 2008/09/24 14:36:02 christos Exp $ */
/*-
* Copyright (c) 2008 Joerg Sonnenberger
@ -26,30 +26,45 @@
*/
#include <sys/cdefs.h>
__RCSID("$NetBSD: strpbrk.c,v 1.16 2008/02/23 15:18:04 christos Exp $");
__RCSID("$NetBSD: strpbrk.c,v 1.17 2008/09/24 14:36:02 christos Exp $");
#include <assert.h>
#include <inttypes.h>
#include <limits.h>
#include <string.h>
#define FAST_STRPBRK 1
#define UC(a) ((unsigned int)(unsigned char)(a))
#ifdef FAST_STRPBRK
#define ADD_NEW_TO_SET(i) (set[inv[i] = idx++] = (i))
#define IS_IN_SET(i) (inv[i] < idx && set[inv[i]] == (i))
#define ADD_TO_SET(i) (IS_IN_SET(i) || ADD_NEW_TO_SET(i))
#else
#define IS_IN_SET(i) (set[(i) >> 3] & idx[(i) & 7])
#define ADD_TO_SET(i) (set[(i) >> 3] |= idx[(i) & 7])
#endif
char *
strpbrk(const char *s, const char *charset)
{
#ifdef FAST_STRPBRK
uint8_t set[256], inv[256], idx = 0;
#else
static const size_t idx[8] = { 1, 2, 4, 8, 16, 32, 64, 128 };
uint8_t set[32];
#define UC(a) ((unsigned int)(unsigned char)(a))
(void)memset(set, 0, sizeof(set));
#endif
_DIAGASSERT(s != NULL);
_DIAGASSERT(charset != NULL);
(void)memset(set, 0, sizeof(set));
for (; *charset != '\0'; ++charset)
set[UC(*charset) >> 3] |= idx[UC(*charset) & 7];
ADD_TO_SET(UC(*charset));
for (; *s != '\0'; ++s)
if (set[UC(*s) >> 3] & idx[UC(*s) & 7])
if (IS_IN_SET(UC(*s)))
return __UNCONST(s);
return NULL;
}