Update and slightly refactor some of the Float trait

Add a constant for negative pi and provide a standalone const
`from_bits`, which can be combined with what we already had in
`hex_float`. Also provide another default method to reduce what needs to
be provided by the macro.

library/compiler-builtins/libm/src/math/support/float_traits.rs

@@ -38,6 +38,7 @@ pub trait Float:
     const MAX: Self;
     const MIN: Self;
     const PI: Self;
+    const NEG_PI: Self;
     const FRAC_PI_2: Self;
 
     /// The bitwidth of the float type
@@ -71,7 +72,9 @@ pub trait Float:
     fn to_bits(self) -> Self::Int;
 
     /// Returns `self` transmuted to `Self::SignedInt`
-    fn to_bits_signed(self) -> Self::SignedInt;
+    fn to_bits_signed(self) -> Self::SignedInt {
+        self.to_bits().signed()
+    }
 
     /// Checks if two floats have the same bit representation. *Except* for NaNs! NaN can be
     /// represented in multiple different ways. This method returns `true` if two NaNs are
@@ -158,7 +161,15 @@ pub trait Float:
 pub type IntTy<F> = <F as Float>::Int;
 
 macro_rules! float_impl {
-    ($ty:ident, $ity:ident, $sity:ident, $expty:ident, $bits:expr, $significand_bits:expr) => {
+    (
+        $ty:ident,
+        $ity:ident,
+        $sity:ident,
+        $expty:ident,
+        $bits:expr,
+        $significand_bits:expr,
+        $from_bits:path
+    ) => {
         impl Float for $ty {
             type Int = $ity;
             type SignedInt = $sity;
@@ -173,13 +184,10 @@ macro_rules! float_impl {
             const NAN: Self = Self::NAN;
             const MAX: Self = -Self::MIN;
             // Sign bit set, saturated mantissa, saturated exponent with last bit zeroed
-            // FIXME(msrv): just use `from_bits` when available
-            // SAFETY: POD cast with no preconditions
-            const MIN: Self = unsafe {
-                mem::transmute::<Self::Int, Self>(Self::Int::MAX & !(1 << Self::SIG_BITS))
-            };
+            const MIN: Self = $from_bits(Self::Int::MAX & !(1 << Self::SIG_BITS));
 
             const PI: Self = core::$ty::consts::PI;
+            const NEG_PI: Self = -Self::PI;
             const FRAC_PI_2: Self = core::$ty::consts::FRAC_PI_2;
 
             const BITS: u32 = $bits;
@@ -193,9 +201,6 @@ macro_rules! float_impl {
             fn to_bits(self) -> Self::Int {
                 self.to_bits()
             }
-            fn to_bits_signed(self) -> Self::SignedInt {
-                self.to_bits() as Self::SignedInt
-            }
             fn is_nan(self) -> bool {
                 self.is_nan()
             }
@@ -220,8 +225,22 @@ macro_rules! float_impl {
 }
 
 #[cfg(f16_enabled)]
-float_impl!(f16, u16, i16, i8, 16, 10);
-float_impl!(f32, u32, i32, i16, 32, 23);
-float_impl!(f64, u64, i64, i16, 64, 52);
+float_impl!(f16, u16, i16, i8, 16, 10, f16::from_bits);
+float_impl!(f32, u32, i32, i16, 32, 23, f32_from_bits);
+float_impl!(f64, u64, i64, i16, 64, 52, f64_from_bits);
 #[cfg(f128_enabled)]
-float_impl!(f128, u128, i128, i16, 128, 112);
+float_impl!(f128, u128, i128, i16, 128, 112, f128::from_bits);
+
+/* FIXME(msrv): vendor some things that are not const stable at our MSRV */
+
+/// `f32::from_bits`
+pub const fn f32_from_bits(bits: u32) -> f32 {
+    // SAFETY: POD cast with no preconditions
+    unsafe { mem::transmute::<u32, f32>(bits) }
+}
+
+/// `f64::from_bits`
+pub const fn f64_from_bits(bits: u64) -> f64 {
+    // SAFETY: POD cast with no preconditions
+    unsafe { mem::transmute::<u64, f64>(bits) }
+}

library/compiler-builtins/libm/src/math/support/hex_float.rs

@@ -2,6 +2,8 @@
 
 #![allow(dead_code)] // FIXME: remove once this gets used
 
+use super::{f32_from_bits, f64_from_bits};
+
 /// Construct a 32-bit float from hex float representation (C-style)
 pub const fn hf32(s: &str) -> f32 {
     f32_from_bits(parse_any(s, 32, 23) as u32)
@@ -159,16 +161,6 @@ const fn hex_digit(c: u8) -> u8 {
 
 /* FIXME(msrv): vendor some things that are not const stable at our MSRV */
 
-/// `f32::from_bits`
-const fn f32_from_bits(v: u32) -> f32 {
-    unsafe { core::mem::transmute(v) }
-}
-
-/// `f64::from_bits`
-const fn f64_from_bits(v: u64) -> f64 {
-    unsafe { core::mem::transmute(v) }
-}
-
 /// `u128::ilog2`
 const fn u128_ilog2(v: u128) -> u32 {
     assert!(v != 0);

library/compiler-builtins/libm/src/math/support/mod.rs

@@ -6,6 +6,7 @@ mod int_traits;
 
 #[allow(unused_imports)]
 pub use float_traits::{Float, IntTy};
+pub(crate) use float_traits::{f32_from_bits, f64_from_bits};
 #[allow(unused_imports)]
 pub use hex_float::{hf32, hf64};
 pub use int_traits::{CastFrom, CastInto, DInt, HInt, Int, MinInt};