/*-
 * 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 <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include "libc_private.h"

#if defined(I_AM_QSORT_R)
typedef int              cmp_t(const void *, const void *, void *);
#elif defined(I_AM_QSORT_R_COMPAT)
typedef int              cmp_t(void *, const void *, const void *);
#elif defined(I_AM_QSORT_S)
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 *);

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

/*
 * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
 */

static inline void
swapfunc(char *a, char *b, size_t es)
{
        char t;

        do {
                t = *a;
                *a++ = *b;
                *b++ = t;
        } while (--es > 0);
}

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

#if defined(I_AM_QSORT_R)
#define CMP(t, x, y) (cmp((x), (y), (t)))
#elif defined(I_AM_QSORT_R_COMPAT)
#define CMP(t, x, y) (cmp((t), (x), (y)))
#elif defined(I_AM_QSORT_S)
#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
#if !defined(I_AM_QSORT_R) && !defined(I_AM_QSORT_R_COMPAT) && !defined(I_AM_QSORT_S)
__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 ));
}

/*
 * The actual qsort() implementation is static to avoid preemptible calls when
 * recursing. Also give them different names for improved debugging.
 */
#if defined(I_AM_QSORT_R)
#define local_qsort local_qsort_r
#elif defined(I_AM_QSORT_R_COMPAT)
#define local_qsort local_qsort_r_compat
#elif defined(I_AM_QSORT_S)
#define local_qsort local_qsort_s
#endif
static void
local_qsort(void *a, size_t n, size_t es, cmp_t *cmp, void *thunk)
{
        char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
        size_t d1, d2;
        int cmp_result;

        /* if there are less than 2 elements, then sorting is not needed */
        if (__predict_false(n < 2))
                return;
loop:
        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)
                                swapfunc(pl, pl - es, 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);
        }
        swapfunc(a, pm, es);
        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) {
                                swapfunc(pa, pb, es);
                                pa += es;
                        }
                        pb += es;
                }
                while (pb <= pc && (cmp_result = CMP(thunk, pc, a)) >= 0) {
                        if (cmp_result == 0) {
                                swapfunc(pc, pd, es);
                                pd -= es;
                        }
                        pc -= es;
                }
                if (pb > pc)
                        break;
                swapfunc(pb, pc, es);
                pb += es;
                pc -= es;
        }

        pn = (char *)a + n * es;
        d1 = MIN(pa - (char *)a, pb - pa);
        vecswap(a, pb - d1, d1);
        /*
         * Cast es to preserve signedness of right-hand side of MIN()
         * expression, to avoid sign ambiguity in the implied comparison.  es
         * is safely within [0, SSIZE_MAX].
         */
        d1 = MIN(pd - pc, pn - pd - (ssize_t)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) {
                        local_qsort(a, d1 / es, es, cmp, thunk);
                }
                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) {
                        local_qsort(pn - d2, d2 / es, es, cmp, thunk);
                }
                if (d1 > es) {
                        /* Iterate rather than recurse to save stack space */
                        /* qsort(a, d1 / es, es, cmp); */
                        n = d1 / es;
                        goto loop;
                }
        }
}

#if defined(I_AM_QSORT_R)
void
(qsort_r)(void *a, size_t n, size_t es, cmp_t *cmp, void *thunk)
{
        local_qsort_r(a, n, es, cmp, thunk);
}
#elif defined(I_AM_QSORT_R_COMPAT)
void
__qsort_r_compat(void *a, size_t n, size_t es, void *thunk, cmp_t *cmp)
{
        local_qsort_r_compat(a, n, es, cmp, thunk);
}
#elif defined(I_AM_QSORT_S)
errno_t
qsort_s(void *a, rsize_t n, rsize_t es, cmp_t *cmp, void *thunk)
{
        if (n > RSIZE_MAX) {
                __throw_constraint_handler_s("qsort_s : n > RSIZE_MAX", EINVAL);
                return (EINVAL);
        } else if (es > RSIZE_MAX) {
                __throw_constraint_handler_s("qsort_s : es > RSIZE_MAX",
                    EINVAL);
                return (EINVAL);
        } else if (n != 0) {
                if (a == NULL) {
                        __throw_constraint_handler_s("qsort_s : a == NULL",
                            EINVAL);
                        return (EINVAL);
                } else if (cmp == NULL) {
                        __throw_constraint_handler_s("qsort_s : cmp == NULL",
                            EINVAL);
                        return (EINVAL);
                } else if (es <= 0) {
                        __throw_constraint_handler_s("qsort_s : es <= 0",
                            EINVAL);
                        return (EINVAL);
                }
        }

        local_qsort_s(a, n, es, cmp, thunk);
        return (0);
}
#else
void
qsort(void *a, size_t n, size_t es, cmp_t *cmp)
{
        local_qsort(a, n, es, cmp, NULL);
}
#endif