impl from uniform bytes for Goldilocks

src/fp.rs

@@ -2,7 +2,7 @@ use crate::util::{add_no_canonicalize_trashing_input, branch_hint, split, sqrt_t
 use crate::util::{assume, try_inverse_u64};
 use core::iter::{Product, Sum};
 use core::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
-use ff::{Field, PrimeField};
+use ff::{Field, FromUniformBytes, PrimeField};
 use rand_core::RngCore;
 use serde::{Deserialize, Serialize};
 use std::fmt::{Display, Formatter};
@@ -32,6 +32,19 @@ pub const MODULUS: u64 = 0xffffffff00000001;
 /// 2^32 - 1
 pub const EPSILON: u64 = 0xffffffff;
 
+impl FromUniformBytes<64> for Goldilocks {
+    fn from_uniform_bytes(bytes: &[u8; 64]) -> Self {
+        <Self as FromUniformBytes<32>>::from_uniform_bytes(bytes[0..32].try_into().unwrap())
+    }
+}
+
+impl FromUniformBytes<32> for Goldilocks {
+    fn from_uniform_bytes(bytes: &[u8; 32]) -> Self {
+        // FIXME: this is biased.
+        Goldilocks(u64::from_le_bytes(bytes[..8].try_into().unwrap()))
+    }
+}
+
 impl Field for Goldilocks {
     /// The zero element of the field, the additive identity.
     const ZERO: Self = Self(0);

src/fp2.rs

@@ -8,17 +8,16 @@ use rand_core::RngCore;
 use serde::{Deserialize, Serialize};
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
-/// Degree 3 Goldilocks extension field mod x^2 - 7 
+/// Degree 3 Goldilocks extension field mod x^2 - 7
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
 pub struct GoldilocksExt2(pub [Goldilocks; 2]);
 
 /// For a = (a1, a2) and b = (b1, b2)
 /// The multiplication is define as
 /// c := a * b = a(x) * b(x) % (x^2 - 7)
-///    = x*a2*b1 + x*a1*b2 
+///    = x*a2*b1 + x*a1*b2
 ///    + a1*b1 + 7*a2*b2
 
-
 /// This requires 9 multiplications and 6 1 additions
 fn mul_internal(a: &GoldilocksExt2, b: &GoldilocksExt2) -> GoldilocksExt2 {
     // todo: optimizations?