Start shifting stuff the actual math out into another file.

src/cryptonum/core.rs

@@ -0,0 +1,17 @@
+use std::cmp::Ordering;
+
+#[inline]
+pub fn generic_cmp(a: &[u64], b: &[u64]) -> Ordering {
+    let mut i = a.len() - 1;
+
+    loop {
+        match a[i].cmp(&b[i]) {
+            Ordering::Equal if i == 0 =>
+                return Ordering::Equal,
+            Ordering::Equal =>
+                i -= 1,
+            res =>
+                return res
+        }
+    }
+}