Added benchmark for mod_multi() and then improved speed by 8%

src/pages/primalitytest.rs

@@ -76,8 +76,7 @@ fn modmult(mut a: u64, mut b: u64, n: u64) -> u64 {
             if (b & 1) == 1 {
                 t = modadd(t, f, n);
             }
-            //TODO: bitshift might be cleaner and faster
-            b = (b as f64 / 2.0).floor() as u64;
+            b >>= 1;
             f = modadd(f, f, n);
         }
         t = modadd(t, f, n);
@@ -373,4 +372,10 @@ mod tests {
         assert_eq!(modmult(3, 3, 4), 1);
         assert_eq!(modmult(110, 4, 7), 6);
     }
+
+    #[bench]
+    fn mod_mult_bench(b: &mut Bencher) {
+        b.iter(|| modmult(3, 3, 4));
+        b.iter(|| modmult(110, 4, 7));
+    }
 }