fields: Use ff::PrimeField instead of FieldExt where possible

src/curves.rs

@@ -5,7 +5,8 @@ use core::cmp;
 use core::fmt::Debug;
 use core::iter::Sum;
 use core::ops::{Add, Mul, Neg, Sub};
-use ff::Field;
+
+use ff::{Field, PrimeField};
 use group::{
     cofactor::{CofactorCurve, CofactorGroup},
     prime::{PrimeCurve, PrimeCurveAffine, PrimeGroup},
@@ -68,7 +69,7 @@ macro_rules! new_curve_impl {
                     let x3 = x.square() * x;
                     let y = (x3 + $name::curve_constant_b()).sqrt();
                     if let Some(y) = Option::<$base>::from(y) {
-                        let sign = y.to_bytes()[0] & 1;
+                        let sign = y.is_odd().unwrap_u8();
                         let y = if ysign ^ sign == 0 { y } else { -y };
 
                         let p = $name_affine {
@@ -465,7 +466,7 @@ macro_rules! new_curve_impl {
                 //
                 // NOTE: We skip the leading bit because it's always unset.
                 for bit in other
-                    .to_bytes()
+                    .to_repr()
                     .iter()
                     .rev()
                     .flat_map(|byte| (0..8).rev().map(move |i| Choice::from((byte >> i) & 1u8)))
@@ -576,7 +577,7 @@ macro_rules! new_curve_impl {
                 //
                 // NOTE: We skip the leading bit because it's always unset.
                 for bit in other
-                    .to_bytes()
+                    .to_repr()
                     .iter()
                     .rev()
                     .flat_map(|byte| (0..8).rev().map(move |i| Choice::from((byte >> i) & 1u8)))
@@ -646,11 +647,11 @@ macro_rules! new_curve_impl {
                 let ysign = Choice::from(tmp[31] >> 7);
                 tmp[31] &= 0b0111_1111;
 
-                $base::from_bytes(&tmp).and_then(|x| {
+                $base::from_repr(tmp).and_then(|x| {
                     CtOption::new(Self::identity(), x.is_zero() & (!ysign)).or_else(|| {
                         let x3 = x.square() * x;
                         (x3 + $name::curve_constant_b()).sqrt().and_then(|y| {
-                            let sign = Choice::from(y.to_bytes()[0] & 1);
+                            let sign = y.is_odd();
 
                             let y = $base::conditional_select(&y, &-y, ysign ^ sign);
 
@@ -678,8 +679,8 @@ macro_rules! new_curve_impl {
                     [0; 32]
                 } else {
                     let (x, y) = (self.x, self.y);
-                    let sign = (y.to_bytes()[0] & 1) << 7;
+                    let sign = y.is_odd().unwrap_u8() << 7;
-                    let mut xbytes = x.to_bytes();
+                    let mut xbytes = x.to_repr();
                     xbytes[31] |= sign;
                     xbytes
                 }

src/fields/fp.rs

@@ -2,6 +2,8 @@ use core::convert::TryInto;
 use core::fmt;
 use core::ops::{Add, Mul, Neg, Sub};
 use lazy_static::lazy_static;
+
+use ff::PrimeField;
 use rand::RngCore;
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
@@ -23,7 +25,7 @@ pub struct Fp(pub(crate) [u64; 4]);
 
 impl fmt::Debug for Fp {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let tmp = self.to_bytes();
+        let tmp = self.to_repr();
         write!(f, "0x")?;
         for &b in tmp.iter().rev() {
             write!(f, "{:02x}", b)?;
@@ -66,8 +68,8 @@ impl PartialEq for Fp {
 
 impl std::cmp::Ord for Fp {
     fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        let left = self.to_bytes();
+        let left = self.to_repr();
-        let right = other.to_bytes();
+        let right = other.to_repr();
         left.iter()
             .zip(right.iter())
             .rev()
@@ -437,13 +439,13 @@ impl Fp {
 
 impl From<Fp> for [u8; 32] {
     fn from(value: Fp) -> [u8; 32] {
-        value.to_bytes()
+        value.to_repr()
     }
 }
 
 impl<'a> From<&'a Fp> for [u8; 32] {
     fn from(value: &'a Fp) -> [u8; 32] {
-        value.to_bytes()
+        value.to_repr()
     }
 }
 
@@ -767,7 +769,7 @@ impl FieldExt for Fp {
 }
 
 #[cfg(test)]
-use ff::{Field, PrimeField};
+use ff::Field;
 
 #[test]
 fn test_inv() {

src/fields/fq.rs

@@ -2,6 +2,8 @@ use core::convert::TryInto;
 use core::fmt;
 use core::ops::{Add, Mul, Neg, Sub};
 use lazy_static::lazy_static;
+
+use ff::PrimeField;
 use rand::RngCore;
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 
@@ -23,7 +25,7 @@ pub struct Fq(pub(crate) [u64; 4]);
 
 impl fmt::Debug for Fq {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let tmp = self.to_bytes();
+        let tmp = self.to_repr();
         write!(f, "0x")?;
         for &b in tmp.iter().rev() {
             write!(f, "{:02x}", b)?;
@@ -66,8 +68,8 @@ impl PartialEq for Fq {
 
 impl std::cmp::Ord for Fq {
     fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        let left = self.to_bytes();
+        let left = self.to_repr();
-        let right = other.to_bytes();
+        let right = other.to_repr();
         left.iter()
             .zip(right.iter())
             .rev()
@@ -437,13 +439,13 @@ impl Fq {
 
 impl From<Fq> for [u8; 32] {
     fn from(value: Fq) -> [u8; 32] {
-        value.to_bytes()
+        value.to_repr()
     }
 }
 
 impl<'a> From<&'a Fq> for [u8; 32] {
     fn from(value: &'a Fq) -> [u8; 32] {
-        value.to_bytes()
+        value.to_repr()
     }
 }
 
@@ -767,7 +769,7 @@ impl FieldExt for Fq {
 }
 
 #[cfg(test)]
-use ff::{Field, PrimeField};
+use ff::Field;
 
 #[test]
 fn test_inv() {