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use primitive_types::U256;

pub fn log2floor(value: U256) -> u64 {
    assert!(value != U256::zero());
    let mut l: u64 = 256;
    for i in 0..4 {
        let i = 3 - i;
        if value.0[i] == 0u64 {
            l -= 64;
        } else {
            l -= value.0[i].leading_zeros() as u64;
            if l == 0 {
                return l
            } else {
                return l - 1;
            }
        }
    }
    return l;
}