void
print_hailstone(integer h)
{
    list l;

    while (h ^ 1) {
        lb_p_integer(l, h);
        h = h & 1 ? 3 * h + 1 : h / 2;
    }

    o_form("hailstone sequence for ~ is ~1 ~ ~ ~ .. ~ ~ ~ ~, it is ~ long\n",
           l[0], l[1], l[2], l[3], l[-3], l[-2], l[-1], 1, ~l + 1);
}

void
max_hailstone(integer x)
{
    integer e, i, m;
    index r;

    m = 0;
    i = 1;
    while (i < x) {
        integer h, k, l;

        h = i;
        l = 1;
        while (h ^ 1) {
            if (i_j_integer(k, r, h)) {
                l += k;
                break;
            } else {
                l += 1;
                h = h & 1 ? 3 * h + 1 : h / 2;
            }
        }

        r[i] = l - 1;

        if (m < l) {
            m = l;
            e = i;
        }

        i += 1;
    }

    o_form("hailstone sequence length for ~ is ~\n", e, m);
}

integer
main(void)
{
    print_hailstone(27);
    max_hailstone(100000);

    return 0;
}