Make `Float` and `Real` depend on the `std` feature

We don't have implementations for many of the methods in `no_std`.  It's
hostile to external implementors if some trait methods are conditional
on a feature, as that feature could be added by anyone in a dependency
tree.  Instead, let's just live without these traits for now.

src/cast.rs

@@ -1,9 +1,9 @@
+use core::f64;
 use core::mem::size_of;
 use core::num::Wrapping;
 
 use identities::Zero;
 use bounds::Bounded;
-use float::Float;
 
 /// A generic trait for converting a value to a number.
 pub trait ToPrimitive {
@@ -228,7 +228,9 @@ macro_rules! impl_to_primitive_float_to_float {
             // NaN and +-inf are cast as they are.
             let n = $slf as f64;
             let max_value: $DstT = ::core::$DstT::MAX;
-            if !Float::is_finite(n) || (-max_value as f64 <= n && n <= max_value as f64) {
+            if n != n || n == f64::INFINITY || n == f64::NEG_INFINITY
+                || (-max_value as f64 <= n && n <= max_value as f64)
+            {
                 Some($slf as $DstT)
             } else {
                 None

src/float.rs

@@ -1,15 +1,24 @@
+#[cfg(feature = "std")]
 use std::mem;
+#[cfg(feature = "std")]
 use std::ops::Neg;
+#[cfg(feature = "std")]
 use std::num::FpCategory;
 
 // Used for default implementation of `epsilon`
+#[cfg(feature = "std")]
 use std::f32;
 
+#[cfg(feature = "std")]
 use {Num, NumCast};
 
 // FIXME: these doctests aren't actually helpful, because they're using and
 // testing the inherent methods directly, not going through `Float`.
 
+/// Generic trait for floating point numbers
+///
+/// This trait is only available with the `std` feature.
+#[cfg(feature = "std")]
 pub trait Float
     : Num
     + Copy
@@ -923,6 +932,7 @@ pub trait Float
     fn integer_decode(self) -> (u64, i16, i8);
 }
 
+#[cfg(feature = "std")]
 macro_rules! float_impl {
     ($T:ident $decode:ident) => (
         impl Float for $T {
@@ -1219,6 +1229,7 @@ macro_rules! float_impl {
     )
 }
 
+#[cfg(feature = "std")]
 fn integer_decode_f32(f: f32) -> (u64, i16, i8) {
     let bits: u32 = unsafe { mem::transmute(f) };
     let sign: i8 = if bits >> 31 == 0 {
@@ -1237,6 +1248,7 @@ fn integer_decode_f32(f: f32) -> (u64, i16, i8) {
     (mantissa as u64, exponent, sign)
 }
 
+#[cfg(feature = "std")]
 fn integer_decode_f64(f: f64) -> (u64, i16, i8) {
     let bits: u64 = unsafe { mem::transmute(f) };
     let sign: i8 = if bits >> 63 == 0 {
@@ -1255,7 +1267,9 @@ fn integer_decode_f64(f: f64) -> (u64, i16, i8) {
     (mantissa, exponent, sign)
 }
 
+#[cfg(feature = "std")]
 float_impl!(f32 integer_decode_f32);
+#[cfg(feature = "std")]
 float_impl!(f64 integer_decode_f64);
 
 macro_rules! float_const_impl {
@@ -1272,7 +1286,7 @@ macro_rules! float_const_impl {
             $(
                 #[inline]
                 fn $constant() -> Self {
-                    ::std::$T::consts::$constant
+                    ::core::$T::consts::$constant
                 }
             )+
         }
@@ -1314,13 +1328,13 @@ float_const_impl! {
     SQRT_2,
 }
 
-#[cfg(test)]
+#[cfg(all(test, feature = "std"))]
 mod tests {
     use Float;
 
     #[test]
     fn convert_deg_rad() {
-        use std::f64::consts;
+        use core::f64::consts;
 
         const DEG_RAD_PAIRS: [(f64, f64); 7] = [
             (0.0, 0.),

src/lib.rs

@@ -24,7 +24,9 @@ use core::num::Wrapping;
 use core::fmt;
 
 pub use bounds::Bounded;
-pub use float::{Float, FloatConst};
+#[cfg(feature = "std")]
+pub use float::Float;
+pub use float::FloatConst;
 // pub use real::Real; // NOTE: Don't do this, it breaks `use num_traits::*;`.
 pub use identities::{Zero, One, zero, one};
 pub use ops::checked::*;
@@ -40,6 +42,7 @@ pub mod sign;
 pub mod ops;
 pub mod bounds;
 pub mod float;
+#[cfg(feature = "std")]
 pub mod real;
 pub mod cast;
 pub mod int;
@@ -187,7 +190,7 @@ impl fmt::Display for ParseFloatError {
 // with this implementation ourselves until we want to make a breaking change.
 // (would have to drop it from `Num` though)
 macro_rules! float_trait_impl {
-    ($name:ident for $($t:ty)*) => ($(
+    ($name:ident for $($t:ident)*) => ($(
         impl $name for $t {
             type FromStrRadixErr = ParseFloatError;
 
@@ -199,9 +202,9 @@ macro_rules! float_trait_impl {
 
                 // Special values
                 match src {
-                    "inf"   => return Ok(Float::infinity()),
-                    "-inf"  => return Ok(Float::neg_infinity()),
-                    "NaN"   => return Ok(Float::nan()),
+                    "inf"   => return Ok(core::$t::INFINITY),
+                    "-inf"  => return Ok(core::$t::NEG_INFINITY),
+                    "NaN"   => return Ok(core::$t::NAN),
                     _       => {},
                 }
 
@@ -242,15 +245,15 @@ macro_rules! float_trait_impl {
                             // if we've not seen any non-zero digits.
                             if prev_sig != 0.0 {
                                 if is_positive && sig <= prev_sig
-                                    { return Ok(Float::infinity()); }
+                                    { return Ok(core::$t::INFINITY); }
                                 if !is_positive && sig >= prev_sig
-                                    { return Ok(Float::neg_infinity()); }
+                                    { return Ok(core::$t::NEG_INFINITY); }
 
                                 // Detect overflow by reversing the shift-and-add process
                                 if is_positive && (prev_sig != (sig - digit as $t) / radix as $t)
-                                    { return Ok(Float::infinity()); }
+                                    { return Ok(core::$t::INFINITY); }
                                 if !is_positive && (prev_sig != (sig + digit as $t) / radix as $t)
-                                    { return Ok(Float::neg_infinity()); }
+                                    { return Ok(core::$t::NEG_INFINITY); }
                             }
                             prev_sig = sig;
                         },
@@ -286,9 +289,9 @@ macro_rules! float_trait_impl {
                                 };
                                 // Detect overflow by comparing to last value
                                 if is_positive && sig < prev_sig
-                                    { return Ok(Float::infinity()); }
+                                    { return Ok(core::$t::INFINITY); }
                                 if !is_positive && sig > prev_sig
-                                    { return Ok(Float::neg_infinity()); }
+                                    { return Ok(core::$t::NEG_INFINITY); }
                                 prev_sig = sig;
                             },
                             None => match c {
@@ -322,9 +325,15 @@ macro_rules! float_trait_impl {
                             None             => return Err(PFE { kind: Invalid }),
                         };
 
+                        #[cfg(feature = "std")]
+                        fn pow(base: $t, exp: usize) -> $t {
+                            Float::powi(base, exp as i32)
+                        }
+                        // otherwise uses the generic `pow` from the root
+
                         match (is_positive, exp) {
-                            (true,  Ok(exp)) => Float::powi(base, exp as i32),
-                            (false, Ok(exp)) => 1.0 / Float::powi(base, exp as i32),
+                            (true,  Ok(exp)) => pow(base, exp),
+                            (false, Ok(exp)) => 1.0 / pow(base, exp),
                             (_, Err(_))      => return Err(PFE { kind: Invalid }),
                         }
                     },

src/real.rs

@@ -10,6 +10,8 @@ use {Num, NumCast, Float};
 ///
 /// See [this Wikipedia article](https://en.wikipedia.org/wiki/Real_data_type)
 /// for a list of data types that could meaningfully implement this trait.
+///
+/// This trait is only available with the `std` feature.
 pub trait Real
     : Num
     + Copy

src/sign.rs

@@ -2,7 +2,7 @@ use core::ops::Neg;
 use core::{f32, f64};
 use core::num::Wrapping;
 
-use {Num, Float};
+use Num;
 
 /// Useful functions for signed numbers (i.e. numbers that can be negative).
 pub trait Signed: Sized + Num + Neg<Output = Self> {
@@ -103,10 +103,24 @@ macro_rules! signed_float_impl {
         impl Signed for $t {
             /// Computes the absolute value. Returns `NAN` if the number is `NAN`.
             #[inline]
+            #[cfg(feature = "std")]
             fn abs(&self) -> $t {
                 (*self).abs()
             }
 
+            /// Computes the absolute value. Returns `NAN` if the number is `NAN`.
+            #[inline]
+            #[cfg(not(feature = "std"))]
+            fn abs(&self) -> $t {
+                if self.is_positive() {
+                    *self
+                } else if self.is_negative() {
+                    -*self
+                } else {
+                    $nan
+                }
+            }
+
             /// 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.
@@ -121,10 +135,29 @@ macro_rules! signed_float_impl {
             /// - `-1.0` if the number is negative, `-0.0` or `NEG_INFINITY`
             /// - `NAN` if the number is NaN
             #[inline]
+            #[cfg(feature = "std")]
             fn signum(&self) -> $t {
+                use Float;
                 Float::signum(*self)
             }
 
+            /// # Returns
+            ///
+            /// - `1.0` if the number is positive, `+0.0` or `INFINITY`
+            /// - `-1.0` if the number is negative, `-0.0` or `NEG_INFINITY`
+            /// - `NAN` if the number is NaN
+            #[inline]
+            #[cfg(not(feature = "std"))]
+            fn signum(&self) -> $t {
+                if self.is_positive() {
+                    1.0
+                } else if self.is_negative() {
+                    -1.0
+                } else {
+                    $nan
+                }
+            }
+
             /// Returns `true` if the number is positive, including `+0.0` and `INFINITY`
             #[inline]
             fn is_positive(&self) -> bool { *self > 0.0 || (1.0 / *self) == $inf }