n = nn<<1;
j=1;
for (i=1; i<n; i+=2) {
    if (j>i) {
        swap(data[j-1], data[i-1]);
        swap(data[j], data[i]);
    }
    m = nn;
    while (m>=2 && j>m) {
        j -= m;
        m >>= 1;
    }
    j += m;
};