/*      $OpenBSD: qsort.c,v 1.18 2017/05/30 14:54:09 millert 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/types.h>
#include <stdlib.h>

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

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

/*
 * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
 *
 * This version differs from Bentley & McIlroy in the following ways:
 *   1. The partition value is swapped into a[0] instead of being
 *      stored out of line.
 *
 *   2. The swap function can swap 32-bit aligned elements on 64-bit
 *      platforms instead of swapping them as byte-aligned.
 *
 *   3. It uses David Musser's introsort algorithm to fall back to
 *      heapsort(3) when the recursion depth reaches 2*lg(n + 1).
 *      This avoids quicksort's quadratic behavior for pathological
 *      input without appreciably changing the average run time.
 *
 *   4. Tail recursion is eliminated when sorting the larger of two
 *      subpartitions to save stack space.
 */
#define SWAPTYPE_BYTEV  1
#define SWAPTYPE_INTV   2
#define SWAPTYPE_LONGV  3
#define SWAPTYPE_INT    4
#define SWAPTYPE_LONG   5

#define TYPE_ALIGNED(TYPE, a, es)                       \
        (((char *)a - (char *)0) % sizeof(TYPE) == 0 && es % sizeof(TYPE) == 0)

#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);                              \
}

static __inline void
swapfunc(char *a, char *b, size_t n, int swaptype)
{
        switch (swaptype) {
        case SWAPTYPE_INT:
        case SWAPTYPE_INTV:
                swapcode(int, a, b, n);
                break;
        case SWAPTYPE_LONG:
        case SWAPTYPE_LONGV:
                swapcode(long, a, b, n);
                break;
        default:
                swapcode(char, a, b, n);
                break;
        }
}

#define swap(a, b)      do {                            \
        switch (swaptype) {                             \
        case SWAPTYPE_INT: {                            \
                int t = *(int *)(a);                    \
                *(int *)(a) = *(int *)(b);              \
                *(int *)(b) = t;                        \
                break;                                  \
            }                                           \
        case SWAPTYPE_LONG: {                           \
                long t = *(long *)(a);                  \
                *(long *)(a) = *(long *)(b);            \
                *(long *)(b) = t;                       \
                break;                                  \
            }                                           \
        default:                                        \
                swapfunc(a, b, es, swaptype);           \
        }                                               \
} while (0)

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

static __inline char *
med3(char *a, char *b, char *c, int (*cmp)(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 ));
}

static void
introsort(char *a, size_t n, size_t es, size_t maxdepth, int swaptype,
    int (*cmp)(const void *, const void *))
{
        char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
        int cmp_result;
        size_t r, s;

loop:   if (n < 7) {
                for (pm = a + es; pm < a + n * es; pm += es)
                        for (pl = pm; pl > a && cmp(pl - es, pl) > 0;
                             pl -= es)
                                swap(pl, pl - es);
                return;
        }
        if (maxdepth == 0) {
                if (heapsort(a, n, es, cmp) == 0)
                        return;
        }
        maxdepth--;
        pm = a + (n / 2) * es;
        if (n > 7) {
                pl = a;
                pn = a + (n - 1) * es;
                if (n > 40) {
                        s = (n / 8) * es;
                        pl = med3(pl, pl + s, pl + 2 * s, cmp);
                        pm = med3(pm - s, pm, pm + s, cmp);
                        pn = med3(pn - 2 * s, pn - s, pn, cmp);
                }
                pm = med3(pl, pm, pn, cmp);
        }
        swap(a, pm);
        pa = pb = a + es;
        pc = pd = 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 = a + n * es;
        r = min(pa - a, pb - pa);
        vecswap(a, pb - r, r);
        r = min(pd - pc, pn - pd - es);
        vecswap(pb, pn - r, r);
        /*
         * To save stack space we sort the smaller side of the partition first
         * using recursion and eliminate tail recursion for the larger side.
         */
        r = pb - pa;
        s = pd - pc;
        if (r < s) {
                /* Recurse for 1st side, iterate for 2nd side. */
                if (s > es) {
                        if (r > es) {
                                introsort(a, r / es, es, maxdepth,
                                    swaptype, cmp);
                        }
                        a = pn - s;
                        n = s / es;
                        goto loop;
                }
        } else {
                /* Recurse for 2nd side, iterate for 1st side. */
                if (r > es) {
                        if (s > es) {
                                introsort(pn - s, s / es, es, maxdepth,
                                    swaptype, cmp);
                        }
                        n = r / es;
                        goto loop;
                }
        }
}

void
qsort(void *a, size_t n, size_t es, int (*cmp)(const void *, const void *))
{
        size_t i, maxdepth = 0;
        int swaptype;

        /* Approximate 2*ceil(lg(n + 1)) */
        for (i = n; i > 0; i >>= 1)
                maxdepth++;
        maxdepth *= 2;

        if (TYPE_ALIGNED(long, a, es))
                swaptype = es == sizeof(long) ? SWAPTYPE_LONG : SWAPTYPE_LONGV;
        else if (sizeof(int) != sizeof(long) && TYPE_ALIGNED(int, a, es))
                swaptype = es == sizeof(int) ? SWAPTYPE_INT : SWAPTYPE_INTV;
        else
                swaptype = SWAPTYPE_BYTEV;

        introsort(a, n, es, maxdepth, swaptype, cmp);

}

DEF_STRONG(qsort);