From 5159ecd9220b505343a5744e01b61825cb734fef Mon Sep 17 00:00:00 2001 From: Trevor Gross Date: Thu, 11 Apr 2024 05:10:37 -0400 Subject: [PATCH] Add a `Debug` impl and some basic functions to `f16` and `f128` `compiler_builtins` uses some convenience functions like `is_nan` and `is_sign_positive`. Add these, as well as a temporary implementation for `Debug` that prints the bit representation. --- library/core/src/fmt/float.rs | 16 ++++++ library/core/src/num/f128.rs | 104 ++++++++++++++++++++++++++++++++++ library/core/src/num/f16.rs | 104 ++++++++++++++++++++++++++++++++++ 3 files changed, 224 insertions(+) diff --git a/library/core/src/fmt/float.rs b/library/core/src/fmt/float.rs index 3bbf5d8770bd2..7f23d3c09567c 100644 --- a/library/core/src/fmt/float.rs +++ b/library/core/src/fmt/float.rs @@ -228,3 +228,19 @@ macro_rules! floating { floating! { f32 } floating! { f64 } + +#[stable(feature = "rust1", since = "1.0.0")] +impl Debug for f16 { + #[inline] + fn fmt(&self, f: &mut Formatter<'_>) -> Result { + write!(f, "{:#06x}", self.to_bits()) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl Debug for f128 { + #[inline] + fn fmt(&self, f: &mut Formatter<'_>) -> Result { + write!(f, "{:#034x}", self.to_bits()) + } +} diff --git a/library/core/src/num/f128.rs b/library/core/src/num/f128.rs index 3bc3e2dbf1242..8a94964c8c5e6 100644 --- a/library/core/src/num/f128.rs +++ b/library/core/src/num/f128.rs @@ -11,6 +11,110 @@ #![unstable(feature = "f128", issue = "116909")] +use crate::mem; + /// Basic mathematical constants. #[unstable(feature = "f128", issue = "116909")] pub mod consts {} + +#[cfg(not(test))] +impl f128 { + // FIXME(f16_f128): almost everything in this `impl` is missing examples and a const + // implementation. Add these once we can run code on all platforms and have f16/f128 in CTFE. + + /// Returns `true` if this value is NaN. + #[inline] + #[must_use] + #[unstable(feature = "f128", issue = "116909")] + #[allow(clippy::eq_op)] // > if you intended to check if the operand is NaN, use `.is_nan()` instead :) + pub const fn is_nan(self) -> bool { + self != self + } + + /// Returns `true` if `self` has a positive sign, including `+0.0`, NaNs with + /// positive sign bit and positive infinity. 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 + /// `is_sign_positive` on a NaN might produce an unexpected result in some cases. + /// See [explanation of NaN as a special value](f32) for more info. + #[inline] + #[must_use] + #[unstable(feature = "f128", issue = "116909")] + pub fn is_sign_positive(self) -> bool { + !self.is_sign_negative() + } + + /// Returns `true` if `self` has a negative sign, including `-0.0`, NaNs with + /// negative sign bit and negative infinity. 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 + /// `is_sign_negative` on a NaN might produce an unexpected result in some cases. + /// See [explanation of NaN as a special value](f32) for more info. + #[inline] + #[must_use] + #[unstable(feature = "f128", issue = "116909")] + pub fn is_sign_negative(self) -> bool { + // IEEE754 says: isSignMinus(x) is true if and only if x has negative sign. isSignMinus + // applies to zeros and NaNs as well. + // SAFETY: This is just transmuting to get the sign bit, it's fine. + (self.to_bits() & (1 << 127)) != 0 + } + + /// Raw transmutation to `u128`. + /// + /// This is currently identical to `transmute::(self)` on all platforms. + /// + /// See [`from_bits`](#method.from_bits) for some discussion of the + /// portability of this operation (there are almost no issues). + /// + /// Note that this function is distinct from `as` casting, which attempts to + /// preserve the *numeric* value, and not the bitwise value. + #[inline] + #[unstable(feature = "f128", issue = "116909")] + #[must_use = "this returns the result of the operation, without modifying the original"] + pub fn to_bits(self) -> u128 { + // SAFETY: `u128` is a plain old datatype so we can always... uh... + // ...look, just pretend you forgot what you just read. + // Stability concerns. + unsafe { mem::transmute(self) } + } + + /// Raw transmutation from `u128`. + /// + /// This is currently identical to `transmute::(v)` on all platforms. + /// It turns out this is incredibly portable, for two reasons: + /// + /// * Floats and Ints have the same endianness on all supported platforms. + /// * IEEE 754 very precisely specifies the bit layout of floats. + /// + /// However there is one caveat: prior to the 2008 version of IEEE 754, how + /// to interpret the NaN signaling bit wasn't actually specified. Most platforms + /// (notably x86 and ARM) picked the interpretation that was ultimately + /// standardized in 2008, but some didn't (notably MIPS). As a result, all + /// signaling NaNs on MIPS are quiet NaNs on x86, and vice-versa. + /// + /// Rather than trying to preserve signaling-ness cross-platform, this + /// implementation favors preserving the exact bits. This means that + /// any payloads encoded in NaNs will be preserved even if the result of + /// this method is sent over the network from an x86 machine to a MIPS one. + /// + /// If the results of this method are only manipulated by the same + /// architecture that produced them, then there is no portability concern. + /// + /// If the input isn't NaN, then there is no portability concern. + /// + /// If you don't care about signalingness (very likely), then there is no + /// portability concern. + /// + /// Note that this function is distinct from `as` casting, which attempts to + /// preserve the *numeric* value, and not the bitwise value. + #[inline] + #[must_use] + #[unstable(feature = "f128", issue = "116909")] + pub fn from_bits(v: u128) -> Self { + // SAFETY: `u128 is a plain old datatype so we can always... uh... + // ...look, just pretend you forgot what you just read. + // Stability concerns. + unsafe { mem::transmute(v) } + } +} diff --git a/library/core/src/num/f16.rs b/library/core/src/num/f16.rs index 969ebdc5690c1..039f5188ba4a6 100644 --- a/library/core/src/num/f16.rs +++ b/library/core/src/num/f16.rs @@ -11,6 +11,110 @@ #![unstable(feature = "f16", issue = "116909")] +use crate::mem; + /// Basic mathematical constants. #[unstable(feature = "f16", issue = "116909")] pub mod consts {} + +#[cfg(not(test))] +impl f16 { + // FIXME(f16_f128): almost everything in this `impl` is missing examples and a const + // implementation. Add these once we can run code on all platforms and have f16/f128 in CTFE. + + /// Returns `true` if this value is NaN. + #[inline] + #[must_use] + #[unstable(feature = "f16", issue = "116909")] + #[allow(clippy::eq_op)] // > if you intended to check if the operand is NaN, use `.is_nan()` instead :) + pub const fn is_nan(self) -> bool { + self != self + } + + /// Returns `true` if `self` has a positive sign, including `+0.0`, NaNs with + /// positive sign bit and positive infinity. 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 + /// `is_sign_positive` on a NaN might produce an unexpected result in some cases. + /// See [explanation of NaN as a special value](f32) for more info. + #[inline] + #[must_use] + #[unstable(feature = "f128", issue = "116909")] + pub fn is_sign_positive(self) -> bool { + !self.is_sign_negative() + } + + /// Returns `true` if `self` has a negative sign, including `-0.0`, NaNs with + /// negative sign bit and negative infinity. 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 + /// `is_sign_negative` on a NaN might produce an unexpected result in some cases. + /// See [explanation of NaN as a special value](f32) for more info. + #[inline] + #[must_use] + #[unstable(feature = "f128", issue = "116909")] + pub fn is_sign_negative(self) -> bool { + // IEEE754 says: isSignMinus(x) is true if and only if x has negative sign. isSignMinus + // applies to zeros and NaNs as well. + // SAFETY: This is just transmuting to get the sign bit, it's fine. + (self.to_bits() & (1 << 15)) != 0 + } + + /// Raw transmutation to `u16`. + /// + /// This is currently identical to `transmute::(self)` on all platforms. + /// + /// See [`from_bits`](#method.from_bits) for some discussion of the + /// portability of this operation (there are almost no issues). + /// + /// Note that this function is distinct from `as` casting, which attempts to + /// preserve the *numeric* value, and not the bitwise value. + #[inline] + #[unstable(feature = "f16", issue = "116909")] + #[must_use = "this returns the result of the operation, without modifying the original"] + pub fn to_bits(self) -> u16 { + // SAFETY: `u16` is a plain old datatype so we can always... uh... + // ...look, just pretend you forgot what you just read. + // Stability concerns. + unsafe { mem::transmute(self) } + } + + /// Raw transmutation from `u16`. + /// + /// This is currently identical to `transmute::(v)` on all platforms. + /// It turns out this is incredibly portable, for two reasons: + /// + /// * Floats and Ints have the same endianness on all supported platforms. + /// * IEEE 754 very precisely specifies the bit layout of floats. + /// + /// However there is one caveat: prior to the 2008 version of IEEE 754, how + /// to interpret the NaN signaling bit wasn't actually specified. Most platforms + /// (notably x86 and ARM) picked the interpretation that was ultimately + /// standardized in 2008, but some didn't (notably MIPS). As a result, all + /// signaling NaNs on MIPS are quiet NaNs on x86, and vice-versa. + /// + /// Rather than trying to preserve signaling-ness cross-platform, this + /// implementation favors preserving the exact bits. This means that + /// any payloads encoded in NaNs will be preserved even if the result of + /// this method is sent over the network from an x86 machine to a MIPS one. + /// + /// If the results of this method are only manipulated by the same + /// architecture that produced them, then there is no portability concern. + /// + /// If the input isn't NaN, then there is no portability concern. + /// + /// If you don't care about signalingness (very likely), then there is no + /// portability concern. + /// + /// Note that this function is distinct from `as` casting, which attempts to + /// preserve the *numeric* value, and not the bitwise value. + #[inline] + #[must_use] + #[unstable(feature = "f16", issue = "116909")] + pub fn from_bits(v: u16) -> Self { + // SAFETY: `u16` is a plain old datatype so we can always... uh... + // ...look, just pretend you forgot what you just read. + // Stability concerns. + unsafe { mem::transmute(v) } + } +}