real
entropy(data b)
{
    integer count, i;
    real ones, zeros;

    ones = zeros = 0;

    i = -(count = ~b);
    while (i) {
        if (b[i] == '0') {
            zeros += 1;
        } else {
            ones += 1;
        }

        i += 1;
    }

    return -(ones /= count) * log2(ones) - (zeros /= count) * log2(zeros);
}

integer
main(void)
{
    data a, b;
    integer i;

    a = "1";
    b = "0";

    o_form("%2d %9d /w12p10d10/ ~\n", 1, ~a, 0r, a);
    o_form("%2d %9d /w12p10d10/ ~\n", 2, ~b, 0r, b);
    i = 3;
    while (i <= 37) {
        bu_copy(a, 0, b);
        o_form("%2d %9d /w12p10d10/ ~\n", i, ~a, entropy(a),
               i < 10 ? a.string : "");
        i += 1;
        b.swap(a);
    }

    return 0;
}