[WIP] Speed test for iterative vs. recursive FFT

Cargo.toml

@@ -19,8 +19,13 @@ thiserror = "1.0"
 
 [dev-dependencies]
 assert_matches = "1.5.0"
+criterion = "0.3"
 modinverse = "0.1.0"
 num-bigint = "0.4.0"
 
+[[bench]]
+name = "fft"
+harness = false
+
 [[example]]
 name = "sum"

benches/fft.rs

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use criterion::{criterion_group, criterion_main, Criterion};
+use prio::fft;
+use prio::finite_field::{Field, FieldElement};
+use prio::polynomial;
+
+pub fn fft(c: &mut Criterion) {
+    let test_sizes = [16, 256, 1024, 4096];
+    for size in test_sizes.iter() {
+        let mut rng = rand::thread_rng();
+        let mut inp = vec![Field::zero(); *size];
+        let mut outp = vec![Field::zero(); *size];
+        for i in 0..*size {
+            inp[i] = Field::rand(&mut rng);
+        }
+
+        // Test recursive FFT, including auxiliary data computation.
+        c.bench_function(&format!("recursive/{}", *size), |b| {
+            b.iter(|| {
+                let mut mem = polynomial::PolyAuxMemory::new(*size / 2);
+                polynomial::poly_fft(
+                    &mut outp,
+                    &inp,
+                    &mem.roots_2n,
+                    *size,
+                    false,
+                    &mut mem.fft_memory,
+                )
+            })
+        });
+
+        // Test recursive FFT, but amortize auxiliary data computation across all of the
+        // invocations of the call.
+        let mut mem = polynomial::PolyAuxMemory::new(*size / 2);
+        c.bench_function(&format!("recursive/{} (amortized)", *size), |b| {
+            b.iter(|| {
+                polynomial::poly_fft(
+                    &mut outp,
+                    &inp,
+                    &mem.roots_2n,
+                    *size,
+                    false,
+                    &mut mem.fft_memory,
+                )
+            })
+        });
+
+        // Test iteratigve FFT.
+        c.bench_function(&format!("iterative/{}", *size), |b| {
+            b.iter(|| fft::discrete_fourier_transform::<Field>(&mut outp, &inp))
+        });
+    }
+}
+
+criterion_group!(benches, fft);
+criterion_main!(benches);

src/lib.rs

@@ -14,7 +14,7 @@ pub mod encrypt;
 pub mod fft;
 pub mod finite_field;
 mod fp;
-mod polynomial;
+pub mod polynomial;
 mod prng;
 pub mod server;
 pub mod util;