Remove FieldExt::{from_bytes, read, to_bytes, write}

- `ff::PrimeField::{from_repr, to_repr}` are direct replacements for
  `FieldExt::{from_bytes, to_bytes}`.
- `FieldExt::{read, write}` were added for reading and writing `halo2`
  proofs, but `halo2::transcript` now handles this internally.

CHANGELOG.md

@@ -19,6 +19,8 @@ and this project adheres to Rust's notion of
     (moved to `SqrtRatio` trait).
   - `FieldExt::{RESCUE_ALPHA, RESCUE_INVALPHA}`
   - `FieldExt::from_u64` (use `From<u64> for ff::PrimeField` instead).
+  - `FieldExt::{from_bytes, read, to_bytes, write}`
+    (use `ff::PrimeField::{from_repr, to_repr}` instead).
 
 ## [0.2.1] - 2021-09-17
 ### Changed

src/arithmetic/fields.rs

@@ -4,20 +4,16 @@
 use core::mem::size_of;
 
 use static_assertions::const_assert;
-use subtle::{Choice, CtOption};
+use subtle::Choice;
+
+#[cfg(not(feature = "std"))]
+use subtle::CtOption;
 
 #[cfg(feature = "std")]
 use super::Group;
 
 #[cfg(feature = "std")]
-use std::{
-    assert,
-    boxed::Box,
-    convert::TryInto,
-    io::{self, Read, Write},
-    marker::PhantomData,
-    vec::Vec,
-};
+use std::{assert, boxed::Box, convert::TryInto, marker::PhantomData, vec::Vec};
 
 const_assert!(size_of::<usize>() >= 4);
 
@@ -85,29 +81,6 @@ pub trait FieldExt: SqrtRatio + From<bool> + Ord + Group<Scalar = Self> {
     /// Obtains a field element congruent to the integer `v`.
     fn from_u128(v: u128) -> Self;
 
-    /// Converts this field element to its normalized, little endian byte
-    /// representation.
-    fn to_bytes(&self) -> [u8; 32];
-
-    /// Writes this element in its normalized, little endian form into a buffer.
-    fn write<W: Write>(&self, writer: &mut W) -> io::Result<()> {
-        let compressed = self.to_bytes();
-        writer.write_all(&compressed[..])
-    }
-
-    /// Attempts to obtain a field element from its normalized, little endian
-    /// byte representation.
-    fn from_bytes(bytes: &[u8; 32]) -> CtOption<Self>;
-
-    /// Reads a normalized, little endian represented field element from a
-    /// buffer.
-    fn read<R: Read>(reader: &mut R) -> io::Result<Self> {
-        let mut compressed = [0u8; 32];
-        reader.read_exact(&mut compressed[..])?;
-        Option::from(Self::from_bytes(&compressed))
-            .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "invalid point encoding in proof"))
-    }
-
     /// Obtains a field element that is congruent to the provided little endian
     /// byte representation of an integer.
     fn from_bytes_wide(bytes: &[u8; 64]) -> Self;

src/fields/fp.rs

@@ -627,7 +627,7 @@ impl PrimeFieldBits for Fp {
     type ReprBits = ReprBits;
 
     fn to_le_bits(&self) -> FieldBits<Self::ReprBits> {
-        let bytes = self.to_bytes();
+        let bytes = self.to_repr();
 
         #[cfg(not(target_pointer_width = "64"))]
         let limbs = [
@@ -741,14 +741,6 @@ impl FieldExt for Fp {
         Fp::from_raw([v as u64, (v >> 64) as u64, 0, 0])
     }
 
-    fn from_bytes(bytes: &[u8; 32]) -> CtOption<Fp> {
-        <Self as ff::PrimeField>::from_repr(*bytes)
-    }
-
-    fn to_bytes(&self) -> [u8; 32] {
-        <Self as ff::PrimeField>::to_repr(self)
-    }
-
     /// Converts a 512-bit little endian integer into
     /// a `Fp` by reducing by the modulus.
     fn from_bytes_wide(bytes: &[u8; 64]) -> Fp {

src/fields/fq.rs

@@ -627,7 +627,7 @@ impl PrimeFieldBits for Fq {
     type ReprBits = ReprBits;
 
     fn to_le_bits(&self) -> FieldBits<Self::ReprBits> {
-        let bytes = self.to_bytes();
+        let bytes = self.to_repr();
 
         #[cfg(not(target_pointer_width = "64"))]
         let limbs = [
@@ -741,14 +741,6 @@ impl FieldExt for Fq {
         Fq::from_raw([v as u64, (v >> 64) as u64, 0, 0])
     }
 
-    fn from_bytes(bytes: &[u8; 32]) -> CtOption<Fq> {
-        <Self as ff::PrimeField>::from_repr(*bytes)
-    }
-
-    fn to_bytes(&self) -> [u8; 32] {
-        <Self as ff::PrimeField>::to_repr(self)
-    }
-
     /// Converts a 512-bit little endian integer into
     /// a `Fq` by reducing by the modulus.
     fn from_bytes_wide(bytes: &[u8; 64]) -> Fq {