Add primes benchmark.

benches/primes.rs

@@ -0,0 +1,44 @@
+#![feature(test)]
+
+///! Test evaluating expressions
+extern crate test;
+
+use rhai::{Engine, OptimizationLevel};
+use test::Bencher;
+
+// This script uses the Sieve of Eratosthenes to calculate prime numbers.
+
+const SCRIPT: &str = r#"
+let now = timestamp();
+
+const MAX_NUMBER_TO_CHECK = 1_000;     // 168 primes <= 1000
+
+let prime_mask = [];
+prime_mask.pad(MAX_NUMBER_TO_CHECK, true);
+
+prime_mask[0] = prime_mask[1] = false;
+
+let total_primes_found = 0;
+
+for p in range(2, MAX_NUMBER_TO_CHECK) {
+    if prime_mask[p] {
+        total_primes_found += 1;
+        let i = 2 * p;
+
+        while i < MAX_NUMBER_TO_CHECK {
+            prime_mask[i] = false;
+            i += p;
+        }
+    }
+}
+"#;
+
+#[bench]
+fn bench_eval_primes(bench: &mut Bencher) {
+    let mut engine = Engine::new();
+    engine.set_optimization_level(OptimizationLevel::None);
+
+    let ast = engine.compile(SCRIPT).unwrap();
+
+    bench.iter(|| engine.consume_ast(&ast).unwrap());
+}