darkfi/src/consensus/ouroboros/utils.rs

use crate::consensus::ouroboros::types::Float10;
use dashu::integer::{IBig, Sign, UBig};
use group::ff::PrimeField;
use log::info;
use pasta_curves::pallas;

pub(crate) fn fbig2ibig(f: Float10) -> IBig {
    info!("fbig -> ibig (f): {}", f);
    let rad = IBig::try_from(10).unwrap();
    let sig = f.repr().significand();
    let exp = f.repr().exponent();
    let val: IBig = if exp >= 0 { sig.clone() * rad.pow(exp as usize) } else { sig.clone() };
    info!("fbig -> ibig (i): {}", val);
    val
}

pub(crate) fn base2ibig(base: pallas::Base) -> IBig {
    //
    let byts: [u8; 32] = base.to_repr();
    let words: [u64; 4] = [
        u64::from_le_bytes(byts[0..8].try_into().expect("")),
        u64::from_le_bytes(byts[8..16].try_into().expect("")),
        u64::from_le_bytes(byts[16..24].try_into().expect("")),
        u64::from_le_bytes(byts[24..32].try_into().expect("")),
    ];
    let uparts = UBig::from_words(&words);
    //TODO both y, and t are positive, but workout the sign for general use
    let ibig = IBig::from_parts(Sign::Positive, uparts);
    ibig
}

pub(crate) fn fbig2base(f: Float10) -> pallas::Base {
    info!("fbig -> base (f): {}", f);
    let val: IBig = fbig2ibig(f);
    let (sign, word) = val.as_sign_words();
    //TODO (res) set pallas base sign, i.e sigma1 is negative.
    let mut words: [u64; 4] = [0, 0, 0, 0];
    for i in 0..word.len() {
        words[i] = word[i];
    }
    let base = match sign {
        Sign::Positive => pallas::Base::from_raw(words),
        Sign::Negative => pallas::Base::from_raw(words).neg(),
    };
    base
}

#[cfg(test)]
mod tests {
    use dashu::integer::IBig;
    use pasta_curves::pallas;

    use crate::consensus::ouroboros::{
        consts::RADIX_BITS,
        types::Float10,
        utils::{base2ibig, fbig2base, fbig2ibig},
    };

    #[test]
    fn dashu_fbig2ibig() {
        let f =
            Float10::from_str_native("234234223.000").unwrap().with_precision(RADIX_BITS).value();
        let i: IBig = fbig2ibig(f);
        let sig = IBig::from(234234223);
        assert_eq!(i, sig);
    }

    #[test]
    fn dashu_test_base2ibig() {
        //
        let fbig: Float10 = Float10::from_str_native(
            "28948022309329048855892746252171976963363056481941560715954676764349967630337",
        )
        .unwrap()
        .with_precision(RADIX_BITS)
        .value();
        let ibig = fbig2ibig(fbig.clone());
        let res_base: pallas::Base = fbig2base(fbig.clone());
        let res_ibig: IBig = base2ibig(res_base);
        assert_eq!(res_ibig, ibig);
    }
}