Optimize Bivariate poly math

core/threshold-algebra/Cargo.toml

@@ -24,11 +24,16 @@ tfhe-versionable.workspace = true
 [dev-dependencies]
 aes-prng.workspace = true
 bc2wrap.workspace = true
+criterion.workspace = true
 num-traits.workspace = true
 paste.workspace = true
 proptest.workspace = true
 rstest.workspace = true
 
+[[bench]]
+name = "bivariate"
+harness = false
+
 [features]
 default = ["extension_degree_4"]
 extension_degree_3 =[]

core/threshold-algebra/benches/bivariate.rs

@@ -0,0 +1,78 @@
+use aes_prng::AesRng;
+use criterion::{BenchmarkId, Criterion, criterion_group, criterion_main};
+use rand::SeedableRng;
+use std::hint::black_box;
+use threshold_algebra::{
+    bivariate::BivariatePoly, galois_rings::degree_4::ResiduePolyF4Z128, structure_traits::Sample,
+};
+
+const DEGREES: [usize; 3] = [1, 4, 13];
+
+fn bivariate_setup(degree: usize) -> (BivariatePoly<ResiduePolyF4Z128>, ResiduePolyF4Z128) {
+    let mut rng = AesRng::seed_from_u64(degree as u64);
+    let secret = ResiduePolyF4Z128::sample(&mut rng);
+    let point = ResiduePolyF4Z128::sample(&mut rng);
+    let poly = BivariatePoly::from_secret(&mut rng, secret, degree);
+    (poly, point)
+}
+
+fn bench_bivariate_sampling(c: &mut Criterion) {
+    let mut group = c.benchmark_group("bivariate/from_secret");
+
+    for degree in DEGREES {
+        group.bench_function(BenchmarkId::from_parameter(degree), |b| {
+            let mut rng = AesRng::seed_from_u64(degree as u64);
+            let secret = ResiduePolyF4Z128::sample(&mut rng);
+            b.iter(|| {
+                black_box(BivariatePoly::from_secret(
+                    &mut rng,
+                    black_box(secret),
+                    black_box(degree),
+                ))
+            });
+        });
+    }
+
+    group.finish();
+}
+
+fn bench_bivariate_evaluation(c: &mut Criterion) {
+    let mut group = c.benchmark_group("bivariate/evaluation");
+
+    for degree in DEGREES {
+        let (poly, point) = bivariate_setup(degree);
+
+        group.bench_function(BenchmarkId::new("partial_x", degree), |b| {
+            b.iter(|| black_box(poly.partial_x_eval(black_box(point))));
+        });
+        group.bench_function(BenchmarkId::new("partial_y", degree), |b| {
+            b.iter(|| black_box(poly.partial_y_eval(black_box(point))));
+        });
+        // Baseline: two separate partial evals, mirroring the code before PR 576.
+        group.bench_function(BenchmarkId::new("partial_x_then_y", degree), |b| {
+            b.iter(|| {
+                let p = black_box(point);
+                (
+                    black_box(poly.partial_x_eval(p)),
+                    black_box(poly.partial_y_eval(p)),
+                )
+            });
+        });
+        // Fused: the path `DoublePoly::from_bivariate` actually uses.
+        group.bench_function(BenchmarkId::new("partial_evaluations", degree), |b| {
+            b.iter(|| black_box(poly.partial_evals(black_box(point))));
+        });
+        group.bench_function(BenchmarkId::new("full", degree), |b| {
+            b.iter(|| black_box(poly.full_eval(black_box(point), black_box(point))));
+        });
+    }
+
+    group.finish();
+}
+
+criterion_group!(
+    bivariate,
+    bench_bivariate_sampling,
+    bench_bivariate_evaluation,
+);
+criterion_main!(bivariate);