Add benchmark for mul_assign

benches/fq_bench.rs

@@ -0,0 +1,17 @@
+#![feature(test)]
+
+extern crate test;
+extern crate jubjub;
+
+use std::ops::MulAssign;
+use test::Bencher;
+use jubjub::Fq;
+
+#[bench]
+fn bench_mul_assign(bencher: &mut Bencher) {
+    let mut n = Fq::new([2, 2, 2, 2]);
+    let m = Fq::new([2, 2, 2, 2]);
+    bencher.iter(move || {
+        n.mul_assign(&m);
+    });
+}

src/fq.rs

@@ -186,6 +186,10 @@ const R2: Fq = Fq([
 ]);
 
 impl Fq {
+    pub fn new(limbs: [u64; 4]) -> Fq {
+        Fq(limbs)
+    }
+
     pub fn zero() -> Fq {
         Fq([0, 0, 0, 0])
     }