diff options
Diffstat (limited to 'library/core/src/num/f64.rs')
| -rw-r--r-- | library/core/src/num/f64.rs | 153 |
1 files changed, 130 insertions, 23 deletions
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs index 75c92c2f8..fd3c18ce2 100644 --- a/library/core/src/num/f64.rs +++ b/library/core/src/num/f64.rs @@ -1,4 +1,4 @@ -//! Constants specific to the `f64` double-precision floating point type. +//! Constants for the `f64` double-precision floating point type. //! //! *[See also the `f64` primitive type][f64].* //! @@ -393,7 +393,7 @@ impl f64 { /// Not a Number (NaN). /// - /// Note that IEEE-745 doesn't define just a single NaN value; + /// Note that IEEE 754 doesn't define just a single NaN value; /// a plethora of bit patterns are considered to be NaN. /// Furthermore, the standard makes a difference /// between a "signaling" and a "quiet" NaN, @@ -624,7 +624,7 @@ impl f64 { } /// Returns `true` if `self` has a positive sign, including `+0.0`, NaNs with - /// positive sign bit and positive infinity. Note that IEEE-745 doesn't assign any + /// 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. @@ -655,7 +655,7 @@ impl f64 { } /// Returns `true` if `self` has a negative sign, including `-0.0`, NaNs with - /// negative sign bit and negative infinity. Note that IEEE-745 doesn't assign any + /// 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. @@ -688,6 +688,106 @@ impl f64 { self.is_sign_negative() } + /// Returns the least number greater than `self`. + /// + /// Let `TINY` be the smallest representable positive `f64`. Then, + /// - if `self.is_nan()`, this returns `self`; + /// - if `self` is [`NEG_INFINITY`], this returns [`MIN`]; + /// - if `self` is `-TINY`, this returns -0.0; + /// - if `self` is -0.0 or +0.0, this returns `TINY`; + /// - if `self` is [`MAX`] or [`INFINITY`], this returns [`INFINITY`]; + /// - otherwise the unique least value greater than `self` is returned. + /// + /// The identity `x.next_up() == -(-x).next_down()` holds for all non-NaN `x`. When `x` + /// is finite `x == x.next_up().next_down()` also holds. + /// + /// ```rust + /// #![feature(float_next_up_down)] + /// // f64::EPSILON is the difference between 1.0 and the next number up. + /// assert_eq!(1.0f64.next_up(), 1.0 + f64::EPSILON); + /// // But not for most numbers. + /// assert!(0.1f64.next_up() < 0.1 + f64::EPSILON); + /// assert_eq!(9007199254740992f64.next_up(), 9007199254740994.0); + /// ``` + /// + /// [`NEG_INFINITY`]: Self::NEG_INFINITY + /// [`INFINITY`]: Self::INFINITY + /// [`MIN`]: Self::MIN + /// [`MAX`]: Self::MAX + #[unstable(feature = "float_next_up_down", issue = "91399")] + #[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")] + pub const fn next_up(self) -> Self { + // We must use strictly integer arithmetic to prevent denormals from + // flushing to zero after an arithmetic operation on some platforms. + const TINY_BITS: u64 = 0x1; // Smallest positive f64. + const CLEAR_SIGN_MASK: u64 = 0x7fff_ffff_ffff_ffff; + + let bits = self.to_bits(); + if self.is_nan() || bits == Self::INFINITY.to_bits() { + return self; + } + + let abs = bits & CLEAR_SIGN_MASK; + let next_bits = if abs == 0 { + TINY_BITS + } else if bits == abs { + bits + 1 + } else { + bits - 1 + }; + Self::from_bits(next_bits) + } + + /// Returns the greatest number less than `self`. + /// + /// Let `TINY` be the smallest representable positive `f64`. Then, + /// - if `self.is_nan()`, this returns `self`; + /// - if `self` is [`INFINITY`], this returns [`MAX`]; + /// - if `self` is `TINY`, this returns 0.0; + /// - if `self` is -0.0 or +0.0, this returns `-TINY`; + /// - if `self` is [`MIN`] or [`NEG_INFINITY`], this returns [`NEG_INFINITY`]; + /// - otherwise the unique greatest value less than `self` is returned. + /// + /// The identity `x.next_down() == -(-x).next_up()` holds for all non-NaN `x`. When `x` + /// is finite `x == x.next_down().next_up()` also holds. + /// + /// ```rust + /// #![feature(float_next_up_down)] + /// let x = 1.0f64; + /// // Clamp value into range [0, 1). + /// let clamped = x.clamp(0.0, 1.0f64.next_down()); + /// assert!(clamped < 1.0); + /// assert_eq!(clamped.next_up(), 1.0); + /// ``` + /// + /// [`NEG_INFINITY`]: Self::NEG_INFINITY + /// [`INFINITY`]: Self::INFINITY + /// [`MIN`]: Self::MIN + /// [`MAX`]: Self::MAX + #[unstable(feature = "float_next_up_down", issue = "91399")] + #[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")] + pub const fn next_down(self) -> Self { + // We must use strictly integer arithmetic to prevent denormals from + // flushing to zero after an arithmetic operation on some platforms. + const NEG_TINY_BITS: u64 = 0x8000_0000_0000_0001; // Smallest (in magnitude) negative f64. + const CLEAR_SIGN_MASK: u64 = 0x7fff_ffff_ffff_ffff; + + let bits = self.to_bits(); + if self.is_nan() || bits == Self::NEG_INFINITY.to_bits() { + return self; + } + + let abs = bits & CLEAR_SIGN_MASK; + let next_bits = if abs == 0 { + NEG_TINY_BITS + } else if bits == abs { + bits - 1 + } else { + bits + 1 + }; + Self::from_bits(next_bits) + } + /// Takes the reciprocal (inverse) of a number, `1/x`. /// /// ``` @@ -744,7 +844,7 @@ impl f64 { /// Returns the maximum of the two numbers, ignoring NaN. /// /// If one of the arguments is NaN, then the other argument is returned. - /// This follows the IEEE-754 2008 semantics for maxNum, except for handling of signaling NaNs; + /// This follows the IEEE 754-2008 semantics for maxNum, except for handling of signaling NaNs; /// this function handles all NaNs the same way and avoids maxNum's problems with associativity. /// This also matches the behavior of libm’s fmax. /// @@ -764,7 +864,7 @@ impl f64 { /// Returns the minimum of the two numbers, ignoring NaN. /// /// If one of the arguments is NaN, then the other argument is returned. - /// This follows the IEEE-754 2008 semantics for minNum, except for handling of signaling NaNs; + /// This follows the IEEE 754-2008 semantics for minNum, except for handling of signaling NaNs; /// this function handles all NaNs the same way and avoids minNum's problems with associativity. /// This also matches the behavior of libm’s fmin. /// @@ -926,10 +1026,14 @@ impl f64 { } } } - // SAFETY: `u64` is a plain old datatype so we can always... uh... - // ...look, just pretend you forgot what you just read. - // Stability concerns. - let rt_f64_to_u64 = |rt| unsafe { mem::transmute::<f64, u64>(rt) }; + + #[inline(always)] // See https://github.com/rust-lang/compiler-builtins/issues/491 + fn rt_f64_to_u64(rt: f64) -> u64 { + // SAFETY: `u64` is a plain old datatype so we can always... uh... + // ...look, just pretend you forgot what you just read. + // Stability concerns. + unsafe { mem::transmute::<f64, u64>(rt) } + } // SAFETY: We use internal implementations that either always work or fail at compile time. unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) } } @@ -940,9 +1044,9 @@ impl f64 { /// 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. + /// * IEEE 754 very precisely specifies the bit layout of floats. /// - /// However there is one caveat: prior to the 2008 version of IEEE-754, how + /// 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 @@ -1019,10 +1123,14 @@ impl f64 { } } } - // SAFETY: `u64` is a plain old datatype so we can always... uh... - // ...look, just pretend you forgot what you just read. - // Stability concerns. - let rt_u64_to_f64 = |rt| unsafe { mem::transmute::<u64, f64>(rt) }; + + #[inline(always)] // See https://github.com/rust-lang/compiler-builtins/issues/491 + fn rt_u64_to_f64(rt: u64) -> f64 { + // SAFETY: `u64` is a plain old datatype so we can always... uh... + // ...look, just pretend you forgot what you just read. + // Stability concerns. + unsafe { mem::transmute::<u64, f64>(rt) } + } // SAFETY: We use internal implementations that either always work or fail at compile time. unsafe { intrinsics::const_eval_select((v,), ct_u64_to_f64, rt_u64_to_f64) } } @@ -1280,15 +1388,14 @@ impl f64 { #[must_use = "method returns a new number and does not mutate the original value"] #[stable(feature = "clamp", since = "1.50.0")] #[inline] - pub fn clamp(self, min: f64, max: f64) -> f64 { + pub fn clamp(mut self, min: f64, max: f64) -> f64 { assert!(min <= max); - let mut x = self; - if x < min { - x = min; + if self < min { + self = min; } - if x > max { - x = max; + if self > max { + self = max; } - x + self } } |