qsort.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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/param.h>
#include <sys/libkern.h>

#ifdef I_AM_QSORT_R
typedef int		 cmp_t(const void *, const void *, void *);
#else
typedef int		 cmp_t(const void *, const void *);
#endif
static inline char	*med3(char *, char *, char *, cmp_t *, void *);
static inline void	 swapfunc(char *, char *, size_t, int, int);

/*
 * 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 *) (parmi);		\
	TYPE *pj = (TYPE *) (parmj);		\
	do { 						\
		TYPE	t = *pi;		\
		*pi++ = *pj;				\
		*pj++ = t;				\
	} while (--i > 0);				\
}

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

static inline void
swapfunc(char *a, char *b, size_t n, int swaptype_long, int swaptype_int)
{
	if (swaptype_long <= 1)
		swapcode(long, a, b, n)
	else if (swaptype_int <= 1)
		swapcode(int, a, b, n)
	else
		swapcode(char, a, b, n)
}

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

#define	vecswap(a, b, n)				\
	if ((n) > 0) swapfunc(a, b, n, swaptype_long, swaptype_int)

#ifdef I_AM_QSORT_R
#define	CMP(t, x, y) (cmp((x), (y), (t)))
#else
#define	CMP(t, x, y) (cmp((x), (y)))
#endif

static inline char *
med3(char *a, char *b, char *c, cmp_t *cmp, void *thunk
#ifndef I_AM_QSORT_R
__unused
#endif
)
{
	return CMP(thunk, a, b) < 0 ?
	       (CMP(thunk, b, c) < 0 ? b : (CMP(thunk, a, c) < 0 ? c : a ))
	      :(CMP(thunk, b, c) > 0 ? b : (CMP(thunk, a, c) < 0 ? a : c ));
}

#ifdef I_AM_QSORT_R
void
(qsort_r)(void *a, size_t n, size_t es, cmp_t *cmp, void *thunk)
#else
#define	thunk NULL
void
qsort(void *a, size_t n, size_t es, cmp_t *cmp)
#endif
{
	char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
	size_t d1, d2;
	int cmp_result;
	int swaptype_long, swaptype_int;

loop:	SWAPINIT(long, a, es);
	SWAPINIT(int, a, es);
	if (n < 7) {
		for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
			for (pl = pm; 
			     pl > (char *)a && CMP(thunk, pl - es, pl) > 0;
			     pl -= es)
				swap(pl, pl - es);
		return;
	}
	pm = (char *)a + (n / 2) * es;
	if (n > 7) {
		pl = a;
		pn = (char *)a + (n - 1) * es;
		if (n > 40) {
			size_t d = (n / 8) * es;

			pl = med3(pl, pl + d, pl + 2 * d, cmp, thunk);
			pm = med3(pm - d, pm, pm + d, cmp, thunk);
			pn = med3(pn - 2 * d, pn - d, pn, cmp, thunk);
		}
		pm = med3(pl, pm, pn, cmp, thunk);
	}
	swap(a, pm);
	pa = pb = (char *)a + es;

	pc = pd = (char *)a + (n - 1) * es;
	for (;;) {
		while (pb <= pc && (cmp_result = CMP(thunk, pb, a)) <= 0) {
			if (cmp_result == 0) {
				swap(pa, pb);
				pa += es;
			}
			pb += es;
		}
		while (pb <= pc && (cmp_result = CMP(thunk, 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;
	d1 = MIN(pa - (char *)a, pb - pa);
	vecswap(a, pb - d1, d1);
	d1 = MIN(pd - pc, pn - pd - es);
	vecswap(pb, pn - d1, d1);

	d1 = pb - pa;
	d2 = pd - pc;
	if (d1 <= d2) {
		/* Recurse on left partition, then iterate on right partition */
		if (d1 > es) {
#ifdef I_AM_QSORT_R
			qsort_r(a, d1 / es, es, cmp, thunk);
#else
			qsort(a, d1 / es, es, cmp);
#endif
		}
		if (d2 > es) {
			/* Iterate rather than recurse to save stack space */
			/* qsort(pn - d2, d2 / es, es, cmp); */
			a = pn - d2;
			n = d2 / es;
			goto loop;
		}
	} else {
		/* Recurse on right partition, then iterate on left partition */
		if (d2 > es) {
#ifdef I_AM_QSORT_R
			qsort_r(pn - d2, d2 / es, es, cmp, thunk);
#else
			qsort(pn - d2, d2 / es, es, cmp);
#endif
		}
		if (d1 > es) {
			/* Iterate rather than recurse to save stack space */
			/* qsort(a, d1 / es, es, cmp); */
			n = d1 / es;
			goto loop;
		}
	}
}