Add a bit length function that's handy for macros.

src/signed/base.rs

@@ -68,6 +68,10 @@ macro_rules! signed_impls {
                 $sname{ negative: false, value: $name::zero() }
             }
 
+            fn bit_length() -> usize {
+                $name::bit_length()
+            }
+ 
             fn is_zero(&self) -> bool {
                 self.value.is_zero()
             }

src/unsigned/base.rs

@@ -8,6 +8,8 @@ pub trait CryptoNum {
     fn is_even(&self) -> bool;
     /// Test if the number is odd.
     fn is_odd(&self) -> bool;
+    /// The size of this number in bits.
+    fn bit_length() -> usize;
     /// Mask off the high parts of the number. In particular, it
     /// zeros the bits above (len * 64).
     fn mask(&mut self, len: usize);
@@ -26,6 +28,10 @@ macro_rules! generate_base
                 $name{ value: [0; $size] }
             }
 
+            fn bit_length() -> usize {
+                return $size * 64;
+            }
+
             fn is_zero(&self) -> bool {
                 self.value.iter().all(|&x| x == 0)
             }
@@ -58,7 +64,6 @@ macro_rules! generate_base
             }
         }
 
-        #[cfg(test)]
         impl fmt::Debug for $name {
             fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                 f.write_str(stringify!($name))?;