luby序列生成代码

static double luby(double y, int x) {

    // Find the finite subsequence that contains index 'x', and the
    // size of that subsequence:
    int size, seq;
    for (size = 1, seq = 0; size < x + 1; seq++, size = 2 * size + 1);

    while (size - 1 != x) {
        size = (size - 1) >> 1;
        seq--;
        x = x % size;
    }

    return pow(y, seq);
}