Added base for Montgomery arithmetic

src/modulus/barrett.rs

@@ -0,0 +1,19 @@
+pub struct BarrettPrecomp<O>(O, O);
+
+impl<O> BarrettPrecomp<O>{
+
+    #[inline(always)]
+    pub fn new(a:O, b: O) -> Self{
+        Self(a, b)
+    }
+
+    #[inline(always)]
+    pub fn value_hi(&self) -> &O{
+        &self.0
+    }
+
+    #[inline(always)]
+    pub fn value_lo(&self) -> &O{
+        &self.1
+    }
+}