Add a simple multiexp benchmark

Cargo.toml

@@ -45,5 +45,9 @@ required-features = ["groth16"]
 name = "batch"
 harness = false
 
+[[bench]]
+name = "slow"
+harness = false
+
 [badges]
 maintenance = { status = "actively-developed" }

benches/slow.rs

@@ -0,0 +1,48 @@
+use bellman::{
+    multicore::Worker,
+    multiexp::{multiexp, FullDensity},
+};
+use bls12_381::{Bls12, Scalar};
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion};
+use ff::{Field, PrimeField};
+use futures::Future;
+use group::{Curve, Group};
+use pairing::Engine;
+use rand_core::SeedableRng;
+use rand_xorshift::XorShiftRng;
+use std::sync::Arc;
+
+fn bench_parts(c: &mut Criterion) {
+    let mut rng = XorShiftRng::from_seed([7; 16]);
+    let samples = 1 << 16;
+
+    let v = Arc::new(
+        (0..samples)
+            .map(|_| Scalar::random(&mut rng))
+            .collect::<Vec<_>>(),
+    );
+    let v_bits = Arc::new(v.iter().map(|e| e.to_le_bits()).collect::<Vec<_>>());
+    let g = Arc::new(
+        (0..samples)
+            .map(|_| <Bls12 as Engine>::G1::random(&mut rng).to_affine())
+            .collect::<Vec<_>>(),
+    );
+
+    let pool = Worker::new();
+
+    c.bench_with_input(
+        BenchmarkId::new("multiexp", samples),
+        &(pool, g, v_bits),
+        |b, (pool, g, v_bits)| {
+            b.iter(|| {
+                let _: <Bls12 as Engine>::G1 =
+                    multiexp(pool, (g.clone(), 0), FullDensity, v_bits.clone())
+                        .wait()
+                        .unwrap();
+            })
+        },
+    );
+}
+
+criterion_group!(benches, bench_parts);
+criterion_main!(benches);