msb.d

size_t msb(ulong x)
{
    assert (x);
    size_t ret = 0;
    auto i = 1 << (6 - 1);
    while (i)
    {
        if (x >> i)
        {
            ret |= i;
            x >>= i;
        }
        i >>= 1;
    }
    return ret;
}