diff --git a/src/libstd/f32.rs b/src/libstd/f32.rs
index e55afc2344f7..d0c64243ee3f 100644
--- a/src/libstd/f32.rs
+++ b/src/libstd/f32.rs
@@ -40,6 +40,7 @@ impl f32 {
     /// assert_eq!(g.floor(), 3.0);
     /// assert_eq!(h.floor(), -4.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn floor(self) -> f32 {
@@ -73,6 +74,7 @@ impl f32 {
     /// assert_eq!(f.ceil(), 4.0);
     /// assert_eq!(g.ceil(), 4.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ceil(self) -> f32 {
@@ -95,6 +97,7 @@ impl f32 {
     /// assert_eq!(f.round(), 3.0);
     /// assert_eq!(g.round(), -3.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn round(self) -> f32 {
@@ -114,6 +117,7 @@ impl f32 {
     /// assert_eq!(g.trunc(), 3.0);
     /// assert_eq!(h.trunc(), -3.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn trunc(self) -> f32 {
@@ -135,6 +139,7 @@ impl f32 {
     /// assert!(abs_difference_x <= f32::EPSILON);
     /// assert!(abs_difference_y <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn fract(self) -> f32 { self - self.trunc() }
@@ -158,6 +163,7 @@ impl f32 {
     ///
     /// assert!(f32::NAN.abs().is_nan());
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn abs(self) -> f32 {
@@ -182,6 +188,7 @@ impl f32 {
     ///
     /// assert!(f32::NAN.signum().is_nan());
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn signum(self) -> f32 {
@@ -367,6 +374,7 @@ impl f32 {
     /// assert!(abs_difference <= f32::EPSILON);
     /// assert!(negative.sqrt().is_nan());
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sqrt(self) -> f32 {
@@ -393,6 +401,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp(self) -> f32 {
@@ -417,6 +426,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp2(self) -> f32 {
@@ -439,6 +449,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln(self) -> f32 {
@@ -485,6 +496,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log2(self) -> f32 {
@@ -508,6 +520,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log10(self) -> f32 {
@@ -565,6 +578,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cbrt(self) -> f32 {
@@ -606,6 +620,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sin(self) -> f32 {
@@ -629,6 +644,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cos(self) -> f32 {
@@ -651,6 +667,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tan(self) -> f32 {
@@ -673,6 +690,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asin(self) -> f32 {
@@ -695,6 +713,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acos(self) -> f32 {
@@ -716,6 +735,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atan(self) -> f32 {
@@ -794,6 +814,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp_m1(self) -> f32 {
@@ -815,6 +836,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln_1p(self) -> f32 {
@@ -838,6 +860,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sinh(self) -> f32 {
@@ -861,6 +884,7 @@ impl f32 {
     /// // Same result
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cosh(self) -> f32 {
@@ -884,6 +908,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tanh(self) -> f32 {
@@ -904,6 +929,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asinh(self) -> f32 {
@@ -928,6 +954,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acosh(self) -> f32 {
@@ -951,6 +978,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= 1e-5);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atanh(self) -> f32 {
diff --git a/src/libstd/f64.rs b/src/libstd/f64.rs
index b35710263009..0878cfd68b48 100644
--- a/src/libstd/f64.rs
+++ b/src/libstd/f64.rs
@@ -40,6 +40,7 @@ impl f64 {
     /// assert_eq!(g.floor(), 3.0);
     /// assert_eq!(h.floor(), -4.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn floor(self) -> f64 {
@@ -57,6 +58,7 @@ impl f64 {
     /// assert_eq!(f.ceil(), 4.0);
     /// assert_eq!(g.ceil(), 4.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ceil(self) -> f64 {
@@ -75,6 +77,7 @@ impl f64 {
     /// assert_eq!(f.round(), 3.0);
     /// assert_eq!(g.round(), -3.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn round(self) -> f64 {
@@ -94,6 +97,7 @@ impl f64 {
     /// assert_eq!(g.trunc(), 3.0);
     /// assert_eq!(h.trunc(), -3.0);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn trunc(self) -> f64 {
@@ -113,6 +117,7 @@ impl f64 {
     /// assert!(abs_difference_x < 1e-10);
     /// assert!(abs_difference_y < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn fract(self) -> f64 { self - self.trunc() }
@@ -136,6 +141,7 @@ impl f64 {
     ///
     /// assert!(f64::NAN.abs().is_nan());
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn abs(self) -> f64 {
@@ -160,6 +166,7 @@ impl f64 {
     ///
     /// assert!(f64::NAN.signum().is_nan());
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn signum(self) -> f64 {
@@ -332,6 +339,7 @@ impl f64 {
     /// assert!(abs_difference < 1e-10);
     /// assert!(negative.sqrt().is_nan());
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sqrt(self) -> f64 {
@@ -356,6 +364,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp(self) -> f64 {
@@ -374,6 +383,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp2(self) -> f64 {
@@ -394,6 +404,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln(self) -> f64 {
@@ -432,6 +443,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log2(self) -> f64 {
@@ -455,6 +467,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log10(self) -> f64 {
@@ -504,6 +517,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cbrt(self) -> f64 {
@@ -543,6 +557,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sin(self) -> f64 {
@@ -562,6 +577,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cos(self) -> f64 {
@@ -580,6 +596,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-14);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tan(self) -> f64 {
@@ -602,6 +619,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asin(self) -> f64 {
@@ -624,6 +642,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acos(self) -> f64 {
@@ -643,6 +662,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atan(self) -> f64 {
@@ -719,6 +739,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp_m1(self) -> f64 {
@@ -740,6 +761,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln_1p(self) -> f64 {
@@ -763,6 +785,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sinh(self) -> f64 {
@@ -786,6 +809,7 @@ impl f64 {
     /// // Same result
     /// assert!(abs_difference < 1.0e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cosh(self) -> f64 {
@@ -809,6 +833,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tanh(self) -> f64 {
@@ -827,6 +852,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asinh(self) -> f64 {
@@ -849,6 +875,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acosh(self) -> f64 {
@@ -872,6 +899,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atanh(self) -> f64 {