Add a benchmark for linear combination

Author: fjarri

k256/bench/scalar.rs

@@ -6,7 +6,7 @@ use criterion::{
 use hex_literal::hex;
 use k256::{
     elliptic_curve::{generic_array::arr, group::ff::PrimeField},
-    ProjectivePoint, Scalar,
+    lincomb, ProjectivePoint, Scalar,
 };
 
 fn test_scalar_x() -> Scalar {
@@ -34,9 +34,18 @@ fn bench_point_mul<'a, M: Measurement>(group: &mut BenchmarkGroup<'a, M>) {
     group.bench_function("point-scalar mul", |b| b.iter(|| &p * &s));
 }
 
+fn bench_point_lincomb<'a, M: Measurement>(group: &mut BenchmarkGroup<'a, M>) {
+    let p = ProjectivePoint::generator();
+    let m = hex!("AA5E28D6A97A2479A65527F7290311A3624D4CC0FA1578598EE3C2613BF99522");
+    let s = Scalar::from_repr(m.into()).unwrap();
+    group.bench_function("lincomb via mul+add", |b| b.iter(|| &p * &s + &p * &s));
+    group.bench_function("lincomb", |b| b.iter(|| lincomb(&p, &p, &s, &s)));
+}
+
 fn bench_high_level(c: &mut Criterion) {
     let mut group = c.benchmark_group("high-level operations");
     bench_point_mul(&mut group);
+    bench_point_lincomb(&mut group);
     group.finish();
 }
 

k256/src/arithmetic.rs

@@ -8,6 +8,7 @@ pub(crate) mod scalar;
 mod util;
 
 pub use field::FieldElement;
+pub use mul::lincomb;
 
 use affine::AffinePoint;
 use projective::ProjectivePoint;

k256/src/lib.rs

@@ -67,7 +67,7 @@ pub mod test_vectors;
 pub use elliptic_curve::{self, bigint::U256};
 
 #[cfg(feature = "arithmetic")]
-pub use arithmetic::{affine::AffinePoint, projective::ProjectivePoint, scalar::Scalar};
+pub use arithmetic::{affine::AffinePoint, lincomb, projective::ProjectivePoint, scalar::Scalar};
 
 #[cfg(feature = "expose-field")]
 pub use arithmetic::FieldElement;