Added base for Montgomery arithmetic

src/modulus/prime.rs

@@ -0,0 +1,19 @@
+use primality_test::is_prime;
+
+pub struct Prime {
+	q: u64,
+}
+
+impl Prime {
+	pub fn new(q: u64) -> Self{
+		assert!(is_prime(q) && q > 2);
+        Self::new_unchecked(q)
+	}
+
+	pub fn new_unchecked(q: u64) -> Self {
+        assert!(q.next_power_of_two().ilog2() <= 61);
+        Self {
+            q,
+        }
+    }
+}