Add trait to serialize field and curve objects directly into raw bytes without Montgomery reduction

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "halo2curves"
-version = "0.2.1"
+version = "0.3.1"
 authors = [
   "Sean Bowe <ewillbefull@gmail.com>",
   "Jack Grigg <jack@z.cash>",
@@ -13,6 +13,10 @@ repository = "https://github.com/kilic/pairing"
 readme = "README.md"
 description = "Elliptic curve implementations and wrappers for halo2 library"
 
+[[bench]]
+name = "less_than"
+harness = false
+
 [dev-dependencies]
 criterion = { version = "0.3", features = ["html_reports"] }
 rand_xorshift = "0.3"

benches/less_than.rs

@@ -0,0 +1,64 @@
+#![allow(unused)]
+
+use criterion::BenchmarkId;
+
+/// Compute a - (b + borrow), returning the result and the new borrow.
+#[inline(always)]
+const fn sbb(a: u64, b: u64, borrow: u64) -> (u64, u64) {
+    let ret = (a as u128).wrapping_sub((b as u128) + ((borrow >> 63) as u128));
+    (ret as u64, (ret >> 64) as u64)
+}
+
+#[inline(always)]
+fn is_less_than(x: &[u64; 4], y: &[u64; 4]) -> bool {
+    match x[3].cmp(&y[3]) {
+        core::cmp::Ordering::Less => return true,
+        core::cmp::Ordering::Greater => return false,
+        _ => {}
+    }
+    match x[2].cmp(&y[2]) {
+        core::cmp::Ordering::Less => return true,
+        core::cmp::Ordering::Greater => return false,
+        _ => {}
+    }
+    match x[1].cmp(&y[1]) {
+        core::cmp::Ordering::Less => return true,
+        core::cmp::Ordering::Greater => return false,
+        _ => {}
+    }
+    x[0].lt(&y[0])
+}
+
+#[inline(always)]
+fn check_underflow(x: &[u64; 4], y: &[u64; 4]) -> bool {
+    let (_, borrow) = sbb(x[0], y[0], 0);
+    let (_, borrow) = sbb(x[1], y[1], borrow);
+    let (_, borrow) = sbb(x[2], y[2], borrow);
+    let (_, borrow) = sbb(x[3], y[3], borrow);
+    borrow >> 63 == 1
+}
+
+use criterion::{criterion_group, criterion_main, Criterion};
+
+pub fn criterion_benchmark(c: &mut Criterion) {
+    let x: [u64; 4] = [(); 4].map(|_| rand::random());
+    let y: [u64; 4] = [(); 4].map(|_| rand::random());
+
+    let mut group = c.benchmark_group("Big less than methods");
+
+    group.bench_with_input(
+        BenchmarkId::new("is_less_than", ""),
+        &(x, y),
+        |b, (x, y)| b.iter(|| is_less_than(x, y)),
+    );
+
+    group.bench_with_input(
+        BenchmarkId::new("check_underflow", ""),
+        &(x, y),
+        |b, (x, y)| b.iter(|| check_underflow(x, y)),
+    );
+    group.finish();
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

src/arithmetic.rs

@@ -15,6 +15,13 @@ pub trait CurveAffineExt: pasta_curves::arithmetic::CurveAffine {
         bases: &[Self],
         base_positions: &[u32],
     );
+
+    /// Unlike the `Coordinates` trait, this just returns the raw affine coordinates without checking `is_on_curve`
+    fn into_coordinates(self) -> (Self::Base, Self::Base) {
+        // fallback implementation
+        let coordinates = self.coordinates().unwrap();
+        (*coordinates.x(), *coordinates.y())
+    }
 }
 
 pub(crate) fn sqrt_tonelli_shanks<F: ff::PrimeField, S: AsRef<[u64]>>(