add correct floating point `min` and `max` methods.

The `std::cmp` functions are not correct for floating point types.

`min(NaN, 2.0)` and `min(2.0, NaN)` return different values, because
these functions assume a total order. Floating point types need special
`min`, `max` and `clamp` functions.

3 files changed, 24 insertions, 2 deletions

diff --git a/src/libstd/num/f32.rs b/src/libstd/num/f32.rs
index a686edef99e..fb56444d265 100644
--- a/src/libstd/num/f32.rs
+++ b/src/libstd/num/f32.rs
@@ -9,6 +9,7 @@
 // except according to those terms.
 
 //! Operations and constants for 32-bits floats (`f32` type)
+
 #[allow(missing_doc)];
 
 use prelude::*;
@@ -312,6 +313,16 @@ impl Primitive for f32 {}
 
 impl Float for f32 {
     #[inline]
+    fn max(self, other: f32) -> f32 {
+        unsafe { cmath::c_float::fmax(self, other) }
+    }
+
+    #[inline]
+    fn min(self, other: f32) -> f32 {
+        unsafe { cmath::c_float::fmin(self, other) }
+    }
+
+    #[inline]
     fn nan() -> f32 { 0.0 / 0.0 }
 
     #[inline]
diff --git a/src/libstd/num/f64.rs b/src/libstd/num/f64.rs
index 026bd651e0e..7889041659a 100644
--- a/src/libstd/num/f64.rs
+++ b/src/libstd/num/f64.rs
@@ -23,8 +23,6 @@ use num::{Zero, One, Bounded, strconv};
 use num;
 use intrinsics;
 
-pub use cmp::{min, max};
-
 macro_rules! delegate(
     (
         $(
@@ -314,6 +312,16 @@ impl Primitive for f64 {}
 
 impl Float for f64 {
     #[inline]
+    fn max(self, other: f64) -> f64 {
+        unsafe { cmath::c_double::fmax(self, other) }
+    }
+
+    #[inline]
+    fn min(self, other: f64) -> f64 {
+        unsafe { cmath::c_double::fmin(self, other) }
+    }
+
+    #[inline]
     fn nan() -> f64 { 0.0 / 0.0 }
 
     #[inline]
diff --git a/src/libstd/num/mod.rs b/src/libstd/num/mod.rs
index 2051eeef60c..2f377a52ef8 100644
--- a/src/libstd/num/mod.rs
+++ b/src/libstd/num/mod.rs
@@ -313,6 +313,9 @@ pub enum FPCategory {
 pub trait Float: Signed
                + Round
                + Primitive {
+    fn max(self, other: Self) -> Self;
+    fn min(self, other: Self) -> Self;
+
     // FIXME (#5527): These should be associated constants
     fn nan() -> Self;
     fn infinity() -> Self;