Added the power method for rational numbers

src/rational.rs

@@ -18,7 +18,7 @@ use std::fmt;
 use std::ops::{Add, Div, Mul, Neg, Rem, Sub};
 use std::str::FromStr;
 
-use traits::{FromPrimitive, Float};
+use traits::{FromPrimitive, Float, PrimInt};
 use bigint::{BigInt, BigUint, Sign};
 use {Num, Signed, Zero, One};
 
@@ -184,6 +184,19 @@ impl<T: Clone + Integer + PartialOrd> Ratio<T> {
     }
 }
 
+impl<T: Clone + Integer + PartialOrd + PrimInt> Ratio<T> {
+    /// Raises the ratio to the power of an exponent
+    #[inline]
+    pub fn pow(&self, expon: i32) -> Ratio<T> {
+        match expon.cmp(&0) {
+            cmp::Ordering::Equal => One::one(),
+            cmp::Ordering::Less => self.recip().pow(-expon),
+            cmp::Ordering::Greater => Ratio::new_raw(self.numer.pow(expon as u32),
+                                                     self.denom.pow(expon as u32)),
+        }
+    }
+}
+
 impl Ratio<BigInt> {
     /// Converts a float into a rational number.
     pub fn from_float<T: Float>(f: T) -> Option<BigRational> {
@@ -758,6 +771,18 @@ mod test {
         assert_eq!(_NEG1_2 * _NEG1_2.recip(), _1);
     }
 
+    #[test]
+    fn test_pow() {
+        assert_eq!(_1_2.pow(2), Ratio::new(1, 4));
+        assert_eq!(_1_2.pow(-2), Ratio::new(4, 1));
+        assert_eq!(_1.pow(1), _1);
+        assert_eq!(_NEG1_2.pow(2), _1_2.pow(2));
+        assert_eq!(_NEG1_2.pow(3), -_1_2.pow(3));
+        assert_eq!(_3_2.pow(0), _1);
+        assert_eq!(_3_2.pow(-1), _3_2.recip());
+        assert_eq!(_3_2.pow(3), Ratio::new(27, 8));
+    }
+
     #[test]
     fn test_to_from_str() {
         fn test(r: Rational, s: String) {