Add benchmarks for Powerset

Cargo.toml

@@ -71,3 +71,7 @@ harness = false
 [[bench]]
 name = "combinations"
 harness = false
+
+[[bench]]
+name = "powerset"
+harness = false

benches/powerset.rs

@@ -0,0 +1,44 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use itertools::Itertools;
+
+// Keep aggregate generated elements the same, regardless of powerset length.
+const TOTAL_ELEMENTS: usize = 1 << 12;
+const fn calc_iters(n: usize) -> usize {
+    TOTAL_ELEMENTS / (1 << n)
+}
+
+fn powerset_n(c: &mut Criterion, n: usize) {
+    let id = format!("powerset {}", n);
+    c.bench_function(id.as_str(), move |b| {
+        b.iter(|| {
+            for _ in 0..calc_iters(n) {
+                for elt in (0..n).powerset() {
+                    black_box(elt);
+                }
+            }
+        })
+    });
+}
+
+fn powerset_0(c: &mut Criterion) { powerset_n(c, 0); }
+
+fn powerset_1(c: &mut Criterion) { powerset_n(c, 1); }
+
+fn powerset_2(c: &mut Criterion) { powerset_n(c, 2); }
+
+fn powerset_4(c: &mut Criterion) { powerset_n(c, 4); }
+
+fn powerset_8(c: &mut Criterion) { powerset_n(c, 8); }
+
+fn powerset_12(c: &mut Criterion) { powerset_n(c, 12); }
+
+criterion_group!(
+    benches,
+    powerset_0,
+    powerset_1,
+    powerset_2,
+    powerset_4,
+    powerset_8,
+    powerset_12,
+);
+criterion_main!(benches);