diff --git a/src/libcore/num/f32.rs b/src/libcore/num/f32.rs
index 580a612aebb4..bdd11200419f 100644
--- a/src/libcore/num/f32.rs
+++ b/src/libcore/num/f32.rs
@@ -312,6 +312,13 @@ impl Signed for f32 {
     #[inline(always)]
     fn abs(&self) -> f32 { abs(*self) }
 
+    ///
+    /// The positive difference of two numbers. Returns `0.0` if the number is less than or
+    /// equal to `other`, otherwise the difference between`self` and `other` is returned.
+    ///
+    #[inline(always)]
+    fn abs_sub(&self, other: &f32) -> f32 { abs_sub(*self, *other) }
+
     ///
     /// # Returns
     ///
@@ -959,7 +966,7 @@ mod tests {
     }
 
     #[test]
-    pub fn test_signed() {
+    pub fn test_abs() {
         assert_eq!(infinity.abs(), infinity);
         assert_eq!(1f32.abs(), 1f32);
         assert_eq!(0f32.abs(), 0f32);
@@ -968,7 +975,24 @@ mod tests {
         assert_eq!(neg_infinity.abs(), infinity);
         assert_eq!((1f32/neg_infinity).abs(), 0f32);
         assert!(NaN.abs().is_NaN());
+    }
 
+    #[test]
+    fn test_abs_sub() {
+        assert_eq!((-1f32).abs_sub(&1f32), 0f32);
+        assert_eq!(1f32.abs_sub(&1f32), 0f32);
+        assert_eq!(1f32.abs_sub(&0f32), 1f32);
+        assert_eq!(1f32.abs_sub(&-1f32), 2f32);
+        assert_eq!(neg_infinity.abs_sub(&0f32), 0f32);
+        assert_eq!(infinity.abs_sub(&1f32), infinity);
+        assert_eq!(0f32.abs_sub(&neg_infinity), infinity);
+        assert_eq!(0f32.abs_sub(&infinity), 0f32);
+        assert!(NaN.abs_sub(&-1f32).is_NaN());
+        assert!(1f32.abs_sub(&NaN).is_NaN());
+    }
+
+    #[test]
+    fn test_signum() {
         assert_eq!(infinity.signum(), 1f32);
         assert_eq!(1f32.signum(), 1f32);
         assert_eq!(0f32.signum(), 1f32);
@@ -977,7 +1001,10 @@ mod tests {
         assert_eq!(neg_infinity.signum(), -1f32);
         assert_eq!((1f32/neg_infinity).signum(), -1f32);
         assert!(NaN.signum().is_NaN());
+    }
 
+    #[test]
+    fn test_is_positive() {
         assert!(infinity.is_positive());
         assert!(1f32.is_positive());
         assert!(0f32.is_positive());
@@ -986,7 +1013,10 @@ mod tests {
         assert!(!neg_infinity.is_positive());
         assert!(!(1f32/neg_infinity).is_positive());
         assert!(!NaN.is_positive());
+    }
 
+    #[test]
+    fn test_is_negative() {
         assert!(!infinity.is_negative());
         assert!(!1f32.is_negative());
         assert!(!0f32.is_negative());
diff --git a/src/libcore/num/f64.rs b/src/libcore/num/f64.rs
index 41fc9cca66e5..7c6246757cd8 100644
--- a/src/libcore/num/f64.rs
+++ b/src/libcore/num/f64.rs
@@ -325,6 +325,13 @@ impl Signed for f64 {
     #[inline(always)]
     fn abs(&self) -> f64 { abs(*self) }
 
+    ///
+    /// The positive difference of two numbers. Returns `0.0` if the number is less than or
+    /// equal to `other`, otherwise the difference between`self` and `other` is returned.
+    ///
+    #[inline(always)]
+    fn abs_sub(&self, other: &f64) -> f64 { abs_sub(*self, *other) }
+
     ///
     /// # Returns
     ///
@@ -594,6 +601,7 @@ impl Float for f64 {
     #[inline(always)]
     fn neg_zero() -> f64 { -0.0 }
 
+    /// Returns `true` if the number is NaN
     #[inline(always)]
     fn is_NaN(&self) -> bool { *self != *self }
 
@@ -603,7 +611,7 @@ impl Float for f64 {
         *self == Float::infinity() || *self == Float::neg_infinity()
     }
 
-    /// Returns `true` if the number is finite
+    /// Returns `true` if the number is not infinite or NaN
     #[inline(always)]
     fn is_finite(&self) -> bool {
         !(self.is_NaN() || self.is_infinite())
@@ -1005,7 +1013,7 @@ mod tests {
     }
 
     #[test]
-    pub fn test_signed() {
+    pub fn test_abs() {
         assert_eq!(infinity.abs(), infinity);
         assert_eq!(1f64.abs(), 1f64);
         assert_eq!(0f64.abs(), 0f64);
@@ -1014,7 +1022,24 @@ mod tests {
         assert_eq!(neg_infinity.abs(), infinity);
         assert_eq!((1f64/neg_infinity).abs(), 0f64);
         assert!(NaN.abs().is_NaN());
+    }
 
+    #[test]
+    fn test_abs_sub() {
+        assert_eq!((-1f64).abs_sub(&1f64), 0f64);
+        assert_eq!(1f64.abs_sub(&1f64), 0f64);
+        assert_eq!(1f64.abs_sub(&0f64), 1f64);
+        assert_eq!(1f64.abs_sub(&-1f64), 2f64);
+        assert_eq!(neg_infinity.abs_sub(&0f64), 0f64);
+        assert_eq!(infinity.abs_sub(&1f64), infinity);
+        assert_eq!(0f64.abs_sub(&neg_infinity), infinity);
+        assert_eq!(0f64.abs_sub(&infinity), 0f64);
+        assert!(NaN.abs_sub(&-1f64).is_NaN());
+        assert!(1f64.abs_sub(&NaN).is_NaN());
+    }
+
+    #[test]
+    fn test_signum() {
         assert_eq!(infinity.signum(), 1f64);
         assert_eq!(1f64.signum(), 1f64);
         assert_eq!(0f64.signum(), 1f64);
@@ -1023,7 +1048,10 @@ mod tests {
         assert_eq!(neg_infinity.signum(), -1f64);
         assert_eq!((1f64/neg_infinity).signum(), -1f64);
         assert!(NaN.signum().is_NaN());
+    }
 
+    #[test]
+    fn test_is_positive() {
         assert!(infinity.is_positive());
         assert!(1f64.is_positive());
         assert!(0f64.is_positive());
@@ -1032,7 +1060,10 @@ mod tests {
         assert!(!neg_infinity.is_positive());
         assert!(!(1f64/neg_infinity).is_positive());
         assert!(!NaN.is_positive());
+    }
 
+    #[test]
+    fn test_is_negative() {
         assert!(!infinity.is_negative());
         assert!(!1f64.is_negative());
         assert!(!0f64.is_negative());
diff --git a/src/libcore/num/float.rs b/src/libcore/num/float.rs
index 95f3a76b8008..35e113094876 100644
--- a/src/libcore/num/float.rs
+++ b/src/libcore/num/float.rs
@@ -734,6 +734,15 @@ impl Signed for float {
     #[inline(always)]
     fn abs(&self) -> float { abs(*self) }
 
+    ///
+    /// The positive difference of two numbers. Returns `0.0` if the number is less than or
+    /// equal to `other`, otherwise the difference between`self` and `other` is returned.
+    ///
+    #[inline(always)]
+    fn abs_sub(&self, other: &float) -> float {
+        (*self as f64).abs_sub(&(*other as f64)) as float
+    }
+
     ///
     /// # Returns
     ///
@@ -978,7 +987,7 @@ mod tests {
     }
 
     #[test]
-    fn test_signed() {
+    fn test_abs() {
         assert_eq!(infinity.abs(), infinity);
         assert_eq!(1f.abs(), 1f);
         assert_eq!(0f.abs(), 0f);
@@ -987,7 +996,24 @@ mod tests {
         assert_eq!(neg_infinity.abs(), infinity);
         assert_eq!((1f/neg_infinity).abs(), 0f);
         assert!(NaN.abs().is_NaN());
+    }
 
+    #[test]
+    fn test_abs_sub() {
+        assert_eq!((-1f).abs_sub(&1f), 0f);
+        assert_eq!(1f.abs_sub(&1f), 0f);
+        assert_eq!(1f.abs_sub(&0f), 1f);
+        assert_eq!(1f.abs_sub(&-1f), 2f);
+        assert_eq!(neg_infinity.abs_sub(&0f), 0f);
+        assert_eq!(infinity.abs_sub(&1f), infinity);
+        assert_eq!(0f.abs_sub(&neg_infinity), infinity);
+        assert_eq!(0f.abs_sub(&infinity), 0f);
+        assert!(NaN.abs_sub(&-1f).is_NaN());
+        assert!(1f.abs_sub(&NaN).is_NaN());
+    }
+
+    #[test]
+    fn test_signum() {
         assert_eq!(infinity.signum(), 1f);
         assert_eq!(1f.signum(), 1f);
         assert_eq!(0f.signum(), 1f);
@@ -996,7 +1022,10 @@ mod tests {
         assert_eq!(neg_infinity.signum(), -1f);
         assert_eq!((1f/neg_infinity).signum(), -1f);
         assert!(NaN.signum().is_NaN());
+    }
 
+    #[test]
+    fn test_is_positive() {
         assert!(infinity.is_positive());
         assert!(1f.is_positive());
         assert!(0f.is_positive());
@@ -1005,7 +1034,10 @@ mod tests {
         assert!(!neg_infinity.is_positive());
         assert!(!(1f/neg_infinity).is_positive());
         assert!(!NaN.is_positive());
+    }
 
+    #[test]
+    fn test_is_negative() {
         assert!(!infinity.is_negative());
         assert!(!1f.is_negative());
         assert!(!0f.is_negative());
diff --git a/src/libcore/num/int-template.rs b/src/libcore/num/int-template.rs
index 95c187a7be22..06a9a0b45627 100644
--- a/src/libcore/num/int-template.rs
+++ b/src/libcore/num/int-template.rs
@@ -264,6 +264,15 @@ impl Signed for T {
         if self.is_negative() { -*self } else { *self }
     }
 
+    ///
+    /// The positive difference of two numbers. Returns `0` if the number is less than or
+    /// equal to `other`, otherwise the difference between`self` and `other` is returned.
+    ///
+    #[inline(always)]
+    fn abs_sub(&self, other: &T) -> T {
+        if *self <= *other { 0 } else { *self - *other }
+    }
+
     ///
     /// # Returns
     ///
@@ -554,21 +563,38 @@ mod tests {
     }
 
     #[test]
-    pub fn test_signed() {
+    pub fn test_abs() {
         assert_eq!((1 as T).abs(), 1 as T);
         assert_eq!((0 as T).abs(), 0 as T);
         assert_eq!((-1 as T).abs(), 1 as T);
+    }
 
+    #[test]
+    fn test_abs_sub() {
+        assert_eq!((-1 as T).abs_sub(&(1 as T)), 0 as T);
+        assert_eq!((1 as T).abs_sub(&(1 as T)), 0 as T);
+        assert_eq!((1 as T).abs_sub(&(0 as T)), 1 as T);
+        assert_eq!((1 as T).abs_sub(&(-1 as T)), 2 as T);
+    }
+
+    #[test]
+    fn test_signum() {
         assert_eq!((1 as T).signum(), 1 as T);
         assert_eq!((0 as T).signum(), 0 as T);
         assert_eq!((-0 as T).signum(), 0 as T);
         assert_eq!((-1 as T).signum(), -1 as T);
+    }
 
+    #[test]
+    fn test_is_positive() {
         assert!((1 as T).is_positive());
         assert!(!(0 as T).is_positive());
         assert!(!(-0 as T).is_positive());
         assert!(!(-1 as T).is_positive());
+    }
 
+    #[test]
+    fn test_is_negative() {
         assert!(!(1 as T).is_negative());
         assert!(!(0 as T).is_negative());
         assert!(!(-0 as T).is_negative());
diff --git a/src/libcore/num/num.rs b/src/libcore/num/num.rs
index 2496ba497dcc..7a71729e3e73 100644
--- a/src/libcore/num/num.rs
+++ b/src/libcore/num/num.rs
@@ -55,7 +55,9 @@ pub trait One {
 pub trait Signed: Num
                 + Neg<Self> {
     fn abs(&self) -> Self;
+    fn abs_sub(&self, other: &Self) -> Self;
     fn signum(&self) -> Self;
+
     fn is_positive(&self) -> bool;
     fn is_negative(&self) -> bool;
 }
diff --git a/src/libstd/num/bigint.rs b/src/libstd/num/bigint.rs
index cd347098e251..a5cf929ed93a 100644
--- a/src/libstd/num/bigint.rs
+++ b/src/libstd/num/bigint.rs
@@ -831,6 +831,11 @@ impl Signed for BigInt {
         }
     }
 
+    #[inline(always)]
+    fn abs_sub(&self, other: &BigInt) -> BigInt {
+        if *self <= *other { Zero::zero() } else { *self - *other }
+    }
+
     #[inline(always)]
     fn signum(&self) -> BigInt {
         match self.sign {
@@ -1920,6 +1925,15 @@ mod bigint_tests {
         check(11, 5, 55);
     }
 
+    #[test]
+    fn test_abs_sub() {
+        assert_eq!((-One::one::<BigInt>()).abs_sub(&One::one()), Zero::zero());
+        assert_eq!(One::one::<BigInt>().abs_sub(&One::one()), Zero::zero());
+        assert_eq!(One::one::<BigInt>().abs_sub(&Zero::zero()), One::one());
+        assert_eq!(One::one::<BigInt>().abs_sub(&-One::one::<BigInt>()),
+                   IntConvertible::from_int(2));
+    }
+
     #[test]
     fn test_to_str_radix() {
         fn check(n: int, ans: &str) {