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File: [cvs.NetBSD.org] / src / lib / libc / stdlib / qsort.c (download)

Revision 1.20, Mon Jun 1 06:37:40 2009 UTC (8 years ago) by yamt
Branch: MAIN
CVS Tags: matt-premerge-20091211, matt-mips64-premerge-20101231, bouyer-quota2-nbase, bouyer-quota2-base, bouyer-quota2
Changes since 1.19: +3 -14 lines

qsort: remove the "switch to insertion sort" optimization because it
causes catastrophic performance for certain inputs.

/*	$NetBSD: qsort.c,v 1.20 2009/06/01 06:37:40 yamt Exp $	*/

/*-
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)qsort.c	8.1 (Berkeley) 6/4/93";
#else
__RCSID("$NetBSD: qsort.c,v 1.20 2009/06/01 06:37:40 yamt Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <assert.h>
#include <errno.h>
#include <stdlib.h>

static inline char	*med3 __P((char *, char *, char *,
    int (*)(const void *, const void *)));
static inline void	 swapfunc __P((char *, char *, size_t, int));

#define min(a, b)	(a) < (b) ? a : b

/*
 * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
 */
#define swapcode(TYPE, parmi, parmj, n) { 		\
	size_t i = (n) / sizeof (TYPE); 		\
	TYPE *pi = (TYPE *)(void *)(parmi); 		\
	TYPE *pj = (TYPE *)(void *)(parmj); 		\
	do { 						\
		TYPE	t = *pi;			\
		*pi++ = *pj;				\
		*pj++ = t;				\
        } while (--i > 0);				\
}

#define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
	es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;

static inline void
swapfunc(char *a, char *b, size_t n, int swaptype)
{

	if (swaptype <= 1) 
		swapcode(long, a, b, n)
	else
		swapcode(char, a, b, n)
}

#define swap(a, b)						\
	if (swaptype == 0) {					\
		long t = *(long *)(void *)(a);			\
		*(long *)(void *)(a) = *(long *)(void *)(b);	\
		*(long *)(void *)(b) = t;			\
	} else							\
		swapfunc(a, b, es, swaptype)

#define vecswap(a, b, n) if ((n) > 0) swapfunc((a), (b), (size_t)(n), swaptype)

static inline char *
med3(char *a, char *b, char *c,
    int (*cmp) __P((const void *, const void *)))
{

	return cmp(a, b) < 0 ?
	       (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a ))
              :(cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c ));
}

void
qsort(void *a, size_t n, size_t es,
    int (*cmp) __P((const void *, const void *)))
{
	char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
	size_t d, r;
	int swaptype, cmp_result;

	_DIAGASSERT(a != NULL);
	_DIAGASSERT(cmp != NULL);

loop:	SWAPINIT(a, es);
	if (n < 7) {
		for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
			for (pl = pm; pl > (char *) a && cmp(pl - es, pl) > 0;
			     pl -= es)
				swap(pl, pl - es);
		return;
	}
	pm = (char *) a + (n / 2) * es;
	if (n > 7) {
		pl = (char *) a;
		pn = (char *) a + (n - 1) * es;
		if (n > 40) {
			d = (n / 8) * es;
			pl = med3(pl, pl + d, pl + 2 * d, cmp);
			pm = med3(pm - d, pm, pm + d, cmp);
			pn = med3(pn - 2 * d, pn - d, pn, cmp);
		}
		pm = med3(pl, pm, pn, cmp);
	}
	swap(a, pm);
	pa = pb = (char *) a + es;

	pc = pd = (char *) a + (n - 1) * es;
	for (;;) {
		while (pb <= pc && (cmp_result = cmp(pb, a)) <= 0) {
			if (cmp_result == 0) {
				swap(pa, pb);
				pa += es;
			}
			pb += es;
		}
		while (pb <= pc && (cmp_result = cmp(pc, a)) >= 0) {
			if (cmp_result == 0) {
				swap(pc, pd);
				pd -= es;
			}
			pc -= es;
		}
		if (pb > pc)
			break;
		swap(pb, pc);
		pb += es;
		pc -= es;
	}

	pn = (char *) a + n * es;
	r = min(pa - (char *) a, pb - pa);
	vecswap(a, pb - r, r);
	r = min((size_t)(pd - pc), pn - pd - es);
	vecswap(pb, pn - r, r);
	if ((r = pb - pa) > es)
		qsort(a, r / es, es, cmp);
	if ((r = pd - pc) > es) { 
		/* Iterate rather than recurse to save stack space */
		a = pn - r;
		n = r / es;
		goto loop;
	}
/*		qsort(pn - r, r / es, es, cmp);*/
}