source: mainline/uspace/lib/c/generic/qsort.c@ 8dab988

/*
 * Copyright (c) 2017 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

/** @addtogroup libc
 * @{
 */

/**
 * @file
 * @brief Quicksort.
 */

#include <qsort.h>
#include <stdbool.h>
#include <stddef.h>

/** Quicksort spec */
typedef struct {
        void *base;
        size_t nmemb;
        size_t size;
        int (*compar)(const void *, const void *, void *);
        void *arg;
} qs_spec_t;

/** Comparison function wrapper.
 *
 * Performs qsort_r comparison using qsort comparison function
 *
 * @param a First element
 * @param b Second element
 * @param arg qsort comparison function
 */
static int compar_wrap(const void *a, const void *b, void *arg)
{
        int (*compar)(const void *, const void *) =
            (int (*)(const void *, const void *))arg;

        return compar(a, b);
}

/** Determine if one element is less-than another element.
 *
 * @param qs Quicksort spec
 * @param i First element index
 * @param j Second element index
 */
static bool elem_lt(qs_spec_t *qs, size_t i, size_t j)
{
        const void *a;
        const void *b;
        int r;

        a = qs->base + i * qs->size;
        b = qs->base + j * qs->size;

        r = qs->compar(a, b, qs->arg);

        return r < 0;
}

/** Swap two elements.
 *
 * @param qs Quicksort spec
 * @param i First element index
 * @param j Second element index
 */
static void elem_swap(qs_spec_t *qs, size_t i, size_t j)
{
        char *a;
        char *b;
        char t;
        size_t k;

        a = qs->base + i * qs->size;
        b = qs->base + j * qs->size;

        for (k = 0; k < qs->size; k++) {
                t = a[k];
                a[k] = b[k];
                b[k] = t;
        }
}

/** Partition a range of indices.
 *
 * @param qs Quicksort spec
 * @param lo Lower bound (inclusive)
 * @param hi Upper bound (inclusive)
 * @return Pivot index
 */
static size_t partition(qs_spec_t *qs, size_t lo, size_t hi)
{
        size_t pivot;
        size_t i, j;

        pivot = lo + (hi - lo) / 2;
        i = lo;
        j = hi;
        while (true) {
                while (elem_lt(qs, i, pivot))
                        ++i;
                while (elem_lt(qs, pivot, j))
                        --j;

                if (i >= j)
                        return j;

                elem_swap(qs, i, j);

                /* Need to follow pivot movement */
                if (i == pivot)
                        pivot = j;
                else if (j == pivot)
                        pivot = i;

                i++;
                j--;
        }
}

/** Sort a range of indices.
 *
 * @param qs Quicksort spec
 * @param lo Lower bound (inclusive)
 * @param hi Upper bound (inclusive)
 */
static void quicksort(qs_spec_t *qs, size_t lo, size_t hi)
{
        size_t p;

        if (lo < hi) {
                p = partition(qs, lo, hi);
                quicksort(qs, lo, p);
                quicksort(qs, p + 1, hi);
        }
}

/** Quicksort.
 *
 * @param base Array to sort
 * @param nmemb Number of array members
 * @param size Size of member in bytes
 * @param compar Comparison function
 */
void qsort(void *base, size_t nmemb, size_t size, int (*compar)(const void *,
    const void *))
{
        qs_spec_t qs;

        if (nmemb == 0)
                return;

        qs.base = base;
        qs.nmemb = nmemb;
        qs.size = size;
        qs.compar = compar_wrap;
        qs.arg = compar;

        quicksort(&qs, 0, nmemb - 1);
}

/** Quicksort with extra argument to comparison function.
 *
 * @param base Array to sort
 * @param nmemb Number of array members
 * @param size Size of member in bytes
 * @param compar Comparison function
 * @param arg Argument to comparison function
 */
void qsort_r(void *base, size_t nmemb, size_t size, int (*compar)(const void *,
    const void *, void *), void *arg)
{
        qs_spec_t qs;

        if (nmemb == 0)
                return;

        qs.base = base;
        qs.nmemb = nmemb;
        qs.size = size;
        qs.compar = compar;
        qs.arg = arg;

        quicksort(&qs, 0, nmemb - 1);
}

/** @}
 */