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Improve impl From<u128> for Fp #573

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Merged
weikengchen merged 1 commit into from
Jan 11, 2023
Merged

Improve impl From<u128> for Fp #573

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21 changes: 12 additions & 9 deletions ff/src/fields/models/fp/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -109,7 +109,7 @@ pub trait FpConfig<const N: usize>: Send + Sync + 'static + Sized {
PartialEq(bound = ""),
Eq(bound = "")
)]
pub struct Fp<P, const N: usize>(
pub struct Fp<P: FpConfig<N>, const N: usize>(
pub BigInt<N>,
#[derivative(Debug = "ignore")]
#[doc(hidden)]
Expand Down Expand Up @@ -388,17 +388,20 @@ impl<P: FpConfig<N>, const N: usize> PartialOrd for Fp<P, N> {
}

impl<P: FpConfig<N>, const N: usize> From<u128> for Fp<P, N> {
fn from(other: u128) -> Self {
let mut default_int = BigInt::default();
fn from(mut other: u128) -> Self {
let mut result = BigInt::default();
if N == 1 {
default_int.0[0] = (other % u128::from(P::MODULUS.0[0])) as u64;
result.0[0] = (other % u128::from(P::MODULUS.0[0])) as u64;
} else if N == 2 || P::MODULUS.0[2..].iter().all(|&x| x == 0) {
let mod_as_u128 = P::MODULUS.0[0] as u128 + ((P::MODULUS.0[1] as u128) << 64);
other %= mod_as_u128;
result.0[0] = ((other << 64) >> 64) as u64;
result.0[1] = (other >> 64) as u64;
} else {
let upper = (other >> 64) as u64;
let lower = ((other << 64) >> 64) as u64;
default_int.0[0] = lower;
default_int.0[1] = upper;
result.0[0] = ((other << 64) >> 64) as u64;
result.0[1] = (other >> 64) as u64;
}
Self::from_bigint(default_int).unwrap()
Self::from_bigint(result).unwrap()
}
}

Expand Down