mergesort3.c

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

static void
dump_intv (int *intv,
           int  count)
{
    int i;
    for (i = 0; i < count; i++) {
        printf("%d ", intv[i]);
    }
}

static void
mergesort (int *intv,
           int *tmp,
           int  count)
{
    if (count == 2) {
        if (intv[0] > intv[1]) {
            int tmp;
            tmp = intv[0];
            intv[0] = intv[1];
            intv[1] = tmp;
        }
    } else if (count > 2) {
        int alen, blen;
        int ia, ib, i;
        int *a, *b;

        alen = count / 2;
        blen = (count + 1) / 2;

        memcpy (tmp, intv, sizeof (int) * count);

        a = &tmp[0];
        b = &tmp[alen];

        mergesort (a, &intv[0], alen);
        mergesort (b, &intv[alen], blen);

        i = 0;
        ia = 0;
        ib = 0;
        while (ia < alen && ib < blen) {
            if (a[ia] < b[ib]) {
                intv[i] = a[ia];
                ++ia;
            } else {
                intv[i] = b[ib];
                ++ib;
            }
            ++i;
        }

        if (ia < alen)
            memcpy (&intv[i], &a[ia], sizeof (int) * (alen - ia));

        if (ib < blen)
            memcpy (&intv[i], &b[ib], sizeof (int) * (blen - ib));
    }
}

int
main (int    argc,
      char **argv)
{
    int i;
    int *numbers, *tmp;

    argc --;
    argv ++;

    numbers = malloc (sizeof (int) * argc);
    tmp = malloc (sizeof (int) * argc);

    for (i = 0; i < argc; i++) {
        numbers[i] = atoi(argv[i]);
    }

    mergesort (numbers, tmp, argc);
    dump_intv (numbers, argc);
    printf ("\n");

    return 0;
}