float types: move copysign, abs, signum to libcore

library/core/src/fmt/float.rs

@@ -13,7 +13,7 @@ macro_rules! impl_general_format {
     ($($t:ident)*) => {
         $(impl GeneralFormat for $t {
             fn already_rounded_value_should_use_exponential(&self) -> bool {
-                let abs = $t::abs_private(*self);
+                let abs = $t::abs(*self);
                 (abs != 0.0 && abs < 1e-4) || abs >= 1e+16
             }
         })*

library/core/src/num/f128.rs

@@ -284,17 +284,6 @@ impl f128 {
         self != self
     }
 
-    // FIXME(#50145): `abs` is publicly unavailable in core due to
-    // concerns about portability, so this implementation is for
-    // private use internally.
-    #[inline]
-    pub(crate) const fn abs_private(self) -> f128 {
-        // SAFETY: This transmutation is fine just like in `to_bits`/`from_bits`.
-        unsafe {
-            mem::transmute::<u128, f128>(mem::transmute::<f128, u128>(self) & !Self::SIGN_MASK)
-        }
-    }
-
     /// Returns `true` if this value is positive infinity or negative infinity, and
     /// `false` otherwise.
     ///
@@ -344,10 +333,11 @@ impl f128 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f128", issue = "116909")]
+    #[rustc_allow_const_fn_unstable(const_float_methods)] // for `abs`
     pub const fn is_finite(self) -> bool {
         // There's no need to handle NaN separately: if self is NaN,
         // the comparison is not true, exactly as desired.
-        self.abs_private() < Self::INFINITY
+        self.abs() < Self::INFINITY
     }
 
     /// Returns `true` if the number is [subnormal].
@@ -835,8 +825,8 @@ impl f128 {
         const HI: f128 = f128::MAX / 2.;
 
         let (a, b) = (self, other);
-        let abs_a = a.abs_private();
-        let abs_b = b.abs_private();
+        let abs_a = a.abs();
+        let abs_b = b.abs();
 
         if abs_a <= HI && abs_b <= HI {
             // Overflow is impossible
@@ -1282,4 +1272,100 @@ impl f128 {
         }
         self
     }
+
+    /// Computes the absolute value of `self`.
+    ///
+    /// This function always returns the precise result.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(f128)]
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    /// let x = 3.5_f128;
+    /// let y = -3.5_f128;
+    ///
+    /// assert_eq!(x.abs(), x);
+    /// assert_eq!(y.abs(), -y);
+    ///
+    /// assert!(f128::NAN.abs().is_nan());
+    /// # }
+    /// ```
+    #[inline]
+    #[unstable(feature = "f128", issue = "116909")]
+    #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    pub const fn abs(self) -> Self {
+        // FIXME(f16_f128): replace with `intrinsics::fabsf128` when available
+        // We don't do this now because LLVM has lowering bugs for f128 math.
+        Self::from_bits(self.to_bits() & !(1 << 127))
+    }
+
+    /// Returns a number that represents the sign of `self`.
+    ///
+    /// - `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
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(f128)]
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    /// let f = 3.5_f128;
+    ///
+    /// assert_eq!(f.signum(), 1.0);
+    /// assert_eq!(f128::NEG_INFINITY.signum(), -1.0);
+    ///
+    /// assert!(f128::NAN.signum().is_nan());
+    /// # }
+    /// ```
+    #[inline]
+    #[unstable(feature = "f128", issue = "116909")]
+    #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    pub const fn signum(self) -> f128 {
+        if self.is_nan() { Self::NAN } else { 1.0_f128.copysign(self) }
+    }
+
+    /// Returns a number composed of the magnitude of `self` and the sign of
+    /// `sign`.
+    ///
+    /// Equal to `self` if the sign of `self` and `sign` are the same, otherwise equal to `-self`.
+    /// If `self` is a NaN, then a NaN with the same payload as `self` and the sign bit of `sign` is
+    /// returned.
+    ///
+    /// If `sign` is a NaN, then this operation will still carry over its sign into the result. Note
+    /// that IEEE 754 doesn't assign any meaning to the sign bit in case of a NaN, and as Rust
+    /// doesn't guarantee that the bit pattern of NaNs are conserved over arithmetic operations, the
+    /// result of `copysign` with `sign` being a NaN might produce an unexpected or non-portable
+    /// result. See the [specification of NaN bit patterns](primitive@f32#nan-bit-patterns) for more
+    /// info.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(f128)]
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    /// let f = 3.5_f128;
+    ///
+    /// assert_eq!(f.copysign(0.42), 3.5_f128);
+    /// assert_eq!(f.copysign(-0.42), -3.5_f128);
+    /// assert_eq!((-f).copysign(0.42), 3.5_f128);
+    /// assert_eq!((-f).copysign(-0.42), -3.5_f128);
+    ///
+    /// assert!(f128::NAN.copysign(1.0).is_nan());
+    /// # }
+    /// ```
+    #[inline]
+    #[unstable(feature = "f128", issue = "116909")]
+    #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    pub const fn copysign(self, sign: f128) -> f128 {
+        // SAFETY: this is actually a safe intrinsic
+        unsafe { intrinsics::copysignf128(self, sign) }
+    }
 }

library/core/src/num/f16.rs

@@ -278,15 +278,6 @@ impl f16 {
         self != self
     }
 
-    // FIXMxE(#50145): `abs` is publicly unavailable in core due to
-    // concerns about portability, so this implementation is for
-    // private use internally.
-    #[inline]
-    pub(crate) const fn abs_private(self) -> f16 {
-        // SAFETY: This transmutation is fine just like in `to_bits`/`from_bits`.
-        unsafe { mem::transmute::<u16, f16>(mem::transmute::<f16, u16>(self) & !Self::SIGN_MASK) }
-    }
-
     /// Returns `true` if this value is positive infinity or negative infinity, and
     /// `false` otherwise.
     ///
@@ -334,10 +325,11 @@ impl f16 {
     #[inline]
     #[must_use]
     #[unstable(feature = "f16", issue = "116909")]
+    #[rustc_allow_const_fn_unstable(const_float_methods)] // for `abs`
     pub const fn is_finite(self) -> bool {
         // There's no need to handle NaN separately: if self is NaN,
         // the comparison is not true, exactly as desired.
-        self.abs_private() < Self::INFINITY
+        self.abs() < Self::INFINITY
     }
 
     /// Returns `true` if the number is [subnormal].
@@ -820,8 +812,8 @@ impl f16 {
         const HI: f16 = f16::MAX / 2.;
 
         let (a, b) = (self, other);
-        let abs_a = a.abs_private();
-        let abs_b = b.abs_private();
+        let abs_a = a.abs();
+        let abs_b = b.abs();
 
         if abs_a <= HI && abs_b <= HI {
             // Overflow is impossible
@@ -1257,4 +1249,99 @@ impl f16 {
         }
         self
     }
+
+    /// Computes the absolute value of `self`.
+    ///
+    /// This function always returns the precise result.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(f16)]
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    /// let x = 3.5_f16;
+    /// let y = -3.5_f16;
+    ///
+    /// assert_eq!(x.abs(), x);
+    /// assert_eq!(y.abs(), -y);
+    ///
+    /// assert!(f16::NAN.abs().is_nan());
+    /// # }
+    /// ```
+    #[inline]
+    #[unstable(feature = "f16", issue = "116909")]
+    #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    pub const fn abs(self) -> Self {
+        // FIXME(f16_f128): replace with `intrinsics::fabsf16` when available
+        Self::from_bits(self.to_bits() & !(1 << 15))
+    }
+
+    /// Returns a number that represents the sign of `self`.
+    ///
+    /// - `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
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(f16)]
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    /// let f = 3.5_f16;
+    ///
+    /// assert_eq!(f.signum(), 1.0);
+    /// assert_eq!(f16::NEG_INFINITY.signum(), -1.0);
+    ///
+    /// assert!(f16::NAN.signum().is_nan());
+    /// # }
+    /// ```
+    #[inline]
+    #[unstable(feature = "f16", issue = "116909")]
+    #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    pub const fn signum(self) -> f16 {
+        if self.is_nan() { Self::NAN } else { 1.0_f16.copysign(self) }
+    }
+
+    /// Returns a number composed of the magnitude of `self` and the sign of
+    /// `sign`.
+    ///
+    /// Equal to `self` if the sign of `self` and `sign` are the same, otherwise equal to `-self`.
+    /// If `self` is a NaN, then a NaN with the same payload as `self` and the sign bit of `sign` is
+    /// returned.
+    ///
+    /// If `sign` is a NaN, then this operation will still carry over its sign into the result. Note
+    /// that IEEE 754 doesn't assign any meaning to the sign bit in case of a NaN, and as Rust
+    /// doesn't guarantee that the bit pattern of NaNs are conserved over arithmetic operations, the
+    /// result of `copysign` with `sign` being a NaN might produce an unexpected or non-portable
+    /// result. See the [specification of NaN bit patterns](primitive@f32#nan-bit-patterns) for more
+    /// info.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(f16)]
+    /// # #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    /// let f = 3.5_f16;
+    ///
+    /// assert_eq!(f.copysign(0.42), 3.5_f16);
+    /// assert_eq!(f.copysign(-0.42), -3.5_f16);
+    /// assert_eq!((-f).copysign(0.42), 3.5_f16);
+    /// assert_eq!((-f).copysign(-0.42), -3.5_f16);
+    ///
+    /// assert!(f16::NAN.copysign(1.0).is_nan());
+    /// # }
+    /// ```
+    #[inline]
+    #[unstable(feature = "f16", issue = "116909")]
+    #[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
+    #[must_use = "method returns a new number and does not mutate the original value"]
+    pub const fn copysign(self, sign: f16) -> f16 {
+        // SAFETY: this is actually a safe intrinsic
+        unsafe { intrinsics::copysignf16(self, sign) }
+    }
 }