Add factorial benchmark

benches/factorial.rs

@@ -0,0 +1,57 @@
+#![feature(test)]
+extern crate test;
+
+use num::{BigUint, One};
+use rayon::prelude::*;
+use rustmp::par_for;
+use std::ops::Mul;
+
+const N: u32 = 9999;
+
+// following functions copied from rayon-demo
+
+/// Compute the Factorial using a plain iterator.
+fn factorial(n: u32) -> BigUint {
+    (1..=n).map(BigUint::from).fold(BigUint::one(), Mul::mul)
+}
+
+#[bench]
+/// Benchmark the Factorial using a plain iterator.
+fn factorial_iterator(b: &mut test::Bencher) {
+    let f = factorial(N);
+    b.iter(|| assert_eq!(factorial(test::black_box(N)), f));
+}
+
+#[bench]
+/// Compute the Factorial using rayon::par_iter.
+fn factorial_par_iter(b: &mut test::Bencher) {
+    fn fact(n: u32) -> BigUint {
+        (1..n + 1)
+            .into_par_iter()
+            .map(BigUint::from)
+            .reduce_with(Mul::mul)
+            .unwrap()
+    }
+
+    let f = factorial(N);
+    b.iter(|| assert_eq!(fact(test::black_box(N)), f));
+}
+
+// end functions copied from rayon-demo
+
+#[bench]
+/// Compute the Factorial using rustmp::par_for.
+fn factorial_rmp(b: &mut test::Bencher) {
+    fn fact(n: u32) -> BigUint {
+        let mut res = BigUint::one();
+        par_for! {
+            for i in 2..n + 1, reduction res#*, {
+                res *= BigUint::from(i);
+            }
+        }
+        res
+    }
+
+    let f = factorial(N);
+    b.iter(|| assert_eq!(fact(test::black_box(N)), f));
+}