Benchmark transpose (#190)

* Benchmark transpose

* fmt

Cargo.toml

@@ -36,6 +36,10 @@ harness = false
 name = "ffts"
 harness = false
 
+[[bench]]
+name = "transpose"
+harness = false
+
 [profile.release]
 opt-level = 3
 #lto = "fat"

benches/transpose.rs

@@ -0,0 +1,26 @@
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion};
+use plonky2::field::crandall_field::CrandallField;
+use plonky2::field::field_types::Field;
+use plonky2::util::transpose;
+
+fn criterion_benchmark(c: &mut Criterion) {
+    type F = CrandallField;
+
+    // In practice, for the matrices we care about, each row is associated with a polynomial of
+    // degree 2^13, and has been low-degree extended to a length of 2^16.
+    const WIDTH: usize = 1 << 16;
+
+    let mut group = c.benchmark_group("transpose");
+
+    // We have matrices with various numbers of polynomials. For example, the witness matrix
+    // involves 100+ polynomials.
+    for height in [5, 50, 100, 150] {
+        group.bench_with_input(BenchmarkId::from_parameter(height), &height, |b, _| {
+            let matrix = (0..height).map(|_| F::rand_vec(WIDTH)).collect::<Vec<_>>();
+            b.iter(|| transpose(&matrix));
+        });
+    }
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

src/util/mod.rs

@@ -35,7 +35,7 @@ pub(crate) fn transpose_poly_values<F: Field>(polys: Vec<PolynomialValues<F>>) -
     transpose(&poly_values)
 }
 
-pub(crate) fn transpose<F: Field>(matrix: &[Vec<F>]) -> Vec<Vec<F>> {
+pub fn transpose<F: Field>(matrix: &[Vec<F>]) -> Vec<Vec<F>> {
     let l = matrix.len();
     let w = matrix[0].len();
     let mut transposed = vec![vec![F::ZERO; l]; w];