Function get_sumset_parameters

smc_range_proof/src/cls_range_proof/util.rs:117–146

Pre-requisites of applying sumset protocol Returns number of digits, sumset boundaries (G), randomness multiple and digits of the adapted value.

(
    value: u64,
    min: u64,
    max: u64,
    base: u16,
)

/// Pre-requisites of applying sumset protocol
/// Returns number of digits, sumset boundaries (G), randomness multiple and digits of the adapted value.
pub fn get_sumset_parameters(
    value: u64,
    min: u64,
    max: u64,
    base: u16,
) -> (u32, Vec<u128>, u16, Vec<u16>) {
    // The protocol works for the range [0, H], so change `value` and set range accordingly.
    // New value becomes value - min
    // New max becomes max-1 because the implemented protocol is asking for the proof in range [min, max) and
    // sumset protocol in the paper is described for range [0, max], i.e. upper bound is inclusive in the paper,
    // but it's not in the implementation
    let (range, randomness_multiple) = get_range_and_randomness_multiple(base, min, max - 1);
    let mut value = (value - min) as u128;
    if randomness_multiple != 1 {
        // range had to be artificially increased so increase the value accordingly. This won't overflow as original value is a u64
        value = value * (base - 1) as u128;
    }

    let l = find_number_of_digits(range, base);
    let G = find_sumset_boundaries(range, base, l);
    let digits = decompose_for_sumset(value, &G, base);
    // Following is only for debugging
    // let mut expected = 0_u64;
    // for j in 0..digits.len() {
    //     assert!(digits[j] < base);
    //     expected += digits[j] as u64 * G[j];
    // }
    // assert_eq!(expected, value);
    (l, G, randomness_multiple, digits)
}

#[cfg(test)]
mod tests {