source: bootcd/isolinux/syslinux-6.03/com32/lib/qsort.c

/*
 * qsort.c
 *
 * This is actually combsort.  It's an O(n log n) algorithm with
 * simplicity/small code size being its main virtue.
 */

#include <stddef.h>
#include <stdlib.h>
#include <string.h>

static inline size_t newgap(size_t gap)
{
    gap = (gap * 10) / 13;
    if (gap == 9 || gap == 10)
        gap = 11;

    if (gap < 1)
        gap = 1;
    return gap;
}

void qsort(void *base, size_t nmemb, size_t size,
           int (*compar) (const void *, const void *))
{
    size_t gap = nmemb;
    size_t i, j;
    char *p1, *p2;
    int swapped;

    if (!nmemb)
        return;

    do {
        gap = newgap(gap);
        swapped = 0;

        for (i = 0, p1 = base; i < nmemb - gap; i++, p1 += size) {
            j = i + gap;
            if (compar(p1, p2 = (char *)base + j * size) > 0) {
                memswap(p1, p2, size);
                swapped = 1;
            }
        }
    } while (gap > 1 || swapped);
}