root/compat/qsort.c

DEFINITIONS

1. msort_with_tmp
2. git_qsort

#include "../git-compat-util.h"

/*
 * A merge sort implementation, simplified from the qsort implementation
 * by Mike Haertel, which is a part of the GNU C Library.
 */

static void msort_with_tmp(void *b, size_t n, size_t s,
                           int (*cmp)(const void *, const void *),
                           char *t)
{
        char *tmp;
        char *b1, *b2;
        size_t n1, n2;

        if (n <= 1)
                return;

        n1 = n / 2;
        n2 = n - n1;
        b1 = b;
        b2 = (char *)b + (n1 * s);

        msort_with_tmp(b1, n1, s, cmp, t);
        msort_with_tmp(b2, n2, s, cmp, t);

        tmp = t;

        while (n1 > 0 && n2 > 0) {
                if (cmp(b1, b2) <= 0) {
                        memcpy(tmp, b1, s);
                        tmp += s;
                        b1 += s;
                        --n1;
                } else {
                        memcpy(tmp, b2, s);
                        tmp += s;
                        b2 += s;
                        --n2;
                }
        }
        if (n1 > 0)
                memcpy(tmp, b1, n1 * s);
        memcpy(b, t, (n - n2) * s);
}

void git_qsort(void *b, size_t n, size_t s,
               int (*cmp)(const void *, const void *))
{
        const size_t size = n * s;
        char buf[1024];

        if (size < sizeof(buf)) {
                /* The temporary array fits on the small on-stack buffer. */
                msort_with_tmp(b, n, s, cmp, buf);
        } else {
                /* It's somewhat large, so malloc it.  */
                char *tmp = xmalloc(size);
                msort_with_tmp(b, n, s, cmp, tmp);
                free(tmp);
        }
}