A very slightly faster modexp.

src/cryptonum/unsigned.rs

@@ -165,23 +165,25 @@ impl UCN {
 
     pub fn fastmodexp(&self, e: &UCN, mu: &BarrettUCN) -> UCN {
         let mut b = self.reduce(&mu);
-        let mut eprime = e.clone();
         let mut result = UCN::from(1 as u8);
 
-        loop {
-            if eprime.is_zero() {
-                return result;
-            }
+        for digit in e.contents.iter() {
+            let mut work = *digit;
 
-            if eprime.is_odd() {
+            for _ in 0..64 {
+                if (work & 0x1) == 1 {
                     result = (result * &b).reduce(&mu);
                 }
 
                 b = (&b * &b).reduce(&mu);
-            eprime >>= 1;
+
+                work >>= 1;
             }
         }
 
+        result
+    }
+
     pub fn to_bytes(&self, len: usize) -> Vec<u8> {
         let mylen = self.contents.len() * 8;
         let mut res = Vec::with_capacity(mylen);