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.

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::*;
@@ -311,6 +312,16 @@ impl Bounded for f32 {
 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 }
 

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(
     (
         $(
@@ -313,6 +311,16 @@ impl Bounded for f64 {
 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 }
 

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;

src/libtest/lib.rs

@@ -1063,7 +1063,7 @@ impl MetricMap {
                 Some(v) => {
                     let delta = v.value - vold.value;
                     let noise = match noise_pct {
-                        None => f64::max(vold.noise.abs(), v.noise.abs()),
+                        None => vold.noise.abs().max(v.noise.abs()),
                         Some(pct) => vold.value * pct / 100.0
                     };
                     if delta.abs() <= noise {