---

yaml
---
r: 148444
b: refs/heads/try2
c: 509283d
h: refs/heads/master
v: v3

Author: brendanzab

[refs]

@@ -5,7 +5,7 @@ refs/heads/snap-stage3: 78a7676898d9f80ab540c6df5d4c9ce35bb50463
 refs/heads/try: 519addf6277dbafccbb4159db4b710c37eaa2ec5
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
-refs/heads/try2: cf56624a4ad7703c8f3fc327b8c385da0a803ea5
+refs/heads/try2: 509283d149bb81cad728b2c1b81f7ab8ceb206e1
 refs/heads/dist-snap: ba4081a5a8573875fed17545846f6f6902c8ba8d
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/try2/src/libstd/num/mod.rs

@@ -304,48 +304,29 @@ pub trait Real: Signed
     fn to_radians(&self) -> Self;
 }
 
-/// Raises a value to the power of exp, using
-/// exponentiation by squaring.
+/// Raises a value to the power of exp, using exponentiation by squaring.
 ///
 /// # Example
 ///
 /// ```rust
 /// use std::num;
 ///
-/// let sixteen = num::pow(2, 4u);
-/// assert_eq!(sixteen, 16);
+/// assert_eq!(num::pow(2, 4), 16);
 /// ```
 #[inline]
-pub fn pow<T: Clone+One+Mul<T, T>>(num: T, exp: uint) -> T {
-    let one: uint = One::one();
-    let num_one: T = One::one();
-
-    if exp.is_zero() { return num_one; }
-    if exp == one { return num.clone(); }
-
-    let mut i: uint = exp;
-    let mut v: T;
-    let mut r: T = num_one;
-
-    // This if is to avoid cloning self.
-    if (i & one) == one {
-        r = r * num;
-        i = i - one;
-    }
-
-    i = i >> one;
-    v = num * num;
-
-    while !i.is_zero() {
-        if (i & one) == one {
-            r = r * v;
-            i = i - one;
+pub fn pow<T: One + Mul<T, T>>(mut base: T, mut exp: uint) -> T {
+    if exp == 1 { base }
+    else {
+        let mut acc = one::<T>();
+        while exp > 0 {
+            if (exp & 1) == 1 {
+                acc = acc * base;
+            }
+            base = base * base;
+            exp = exp >> 1;
         }
-        i = i >> one;
-        v = v * v;
+        acc
     }
-
-    r
 }
 
 /// Raise a number to a power.
@@ -1670,17 +1651,24 @@ mod tests {
 
     #[test]
     fn test_pow() {
-        fn assert_pow<T: Eq+Clone+One+Mul<T, T>>(num: T, exp: uint) -> () {
-            assert_eq!(num::pow(num.clone(), exp),
-                       range(1u, exp).fold(num.clone(), |acc, _| acc * num));
+        fn naive_pow<T: One + Mul<T, T>>(base: T, exp: uint) -> T {
+            range(0, exp).fold(one::<T>(), |acc, _| acc * base)
         }
-
-        assert_eq!(num::pow(3, 0), 1);
-        assert_eq!(num::pow(5, 1), 5);
-        assert_pow(-4, 2);
-        assert_pow(8, 3);
-        assert_pow(8, 5);
-        assert_pow(2u64, 50);
+        macro_rules! assert_pow(
+            (($num:expr, $exp:expr) => $expected:expr) => {{
+                let result = pow($num, $exp);
+                assert_eq!(result, $expected);
+                assert_eq!(result, naive_pow($num, $exp));
+            }}
+        )
+        assert_pow!((3,    0 ) => 1);
+        assert_pow!((5,    1 ) => 5);
+        assert_pow!((-4,   2 ) => 16);
+        assert_pow!((0.5,  5 ) => 0.03125);
+        assert_pow!((8,    3 ) => 512);
+        assert_pow!((8.0,  5 ) => 32768.0);
+        assert_pow!((8.5,  5 ) => 44370.53125);
+        assert_pow!((2u64, 50) => 1125899906842624);
     }
 }