Merge pull request #179 from m1el/issue178_exp2_wrap

Fixed u32 overflow in exp2

Author: alexcrichton

src/math/exp2.rs

@@ -373,7 +373,7 @@ pub fn exp2(mut x: f64) -> f64 {
     /* Reduce x, computing z, i0, and k. */
     let ui = f64::to_bits(x + redux);
     let mut i0 = ui as u32;
-    i0 += TBLSIZE as u32 / 2;
+    i0 = i0.wrapping_add(TBLSIZE as u32 / 2);
     let ku = i0 / TBLSIZE as u32 * TBLSIZE as u32;
     let ki = ku as i32 / TBLSIZE as i32;
     i0 %= TBLSIZE as u32;
@@ -387,3 +387,9 @@ pub fn exp2(mut x: f64) -> f64 {
 
     scalbn(r, ki)
 }
+
+#[test]
+fn i0_wrap_test() {
+    let x = -3.0 / 256.0;
+    assert_eq!(exp2(x), f64::from_bits(0x3fefbdba3692d514));
+}