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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
commit | 26a029d407be480d791972afb5975cf62c9360a6 (patch) | |
tree | f435a8308119effd964b339f76abb83a57c29483 /third_party/rust/serde_json/src/lexical/float.rs | |
parent | Initial commit. (diff) | |
download | firefox-26a029d407be480d791972afb5975cf62c9360a6.tar.xz firefox-26a029d407be480d791972afb5975cf62c9360a6.zip |
Adding upstream version 124.0.1.upstream/124.0.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'third_party/rust/serde_json/src/lexical/float.rs')
-rw-r--r-- | third_party/rust/serde_json/src/lexical/float.rs | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/third_party/rust/serde_json/src/lexical/float.rs b/third_party/rust/serde_json/src/lexical/float.rs new file mode 100644 index 0000000000..2d434a29cb --- /dev/null +++ b/third_party/rust/serde_json/src/lexical/float.rs @@ -0,0 +1,183 @@ +// Adapted from https://github.com/Alexhuszagh/rust-lexical. + +// FLOAT TYPE + +use super::num::*; +use super::rounding::*; +use super::shift::*; + +/// Extended precision floating-point type. +/// +/// Private implementation, exposed only for testing purposes. +#[doc(hidden)] +#[derive(Clone, Copy, Debug, PartialEq, Eq)] +pub(crate) struct ExtendedFloat { + /// Mantissa for the extended-precision float. + pub mant: u64, + /// Binary exponent for the extended-precision float. + pub exp: i32, +} + +impl ExtendedFloat { + // PROPERTIES + + // OPERATIONS + + /// Multiply two normalized extended-precision floats, as if by `a*b`. + /// + /// The precision is maximal when the numbers are normalized, however, + /// decent precision will occur as long as both values have high bits + /// set. The result is not normalized. + /// + /// Algorithm: + /// 1. Non-signed multiplication of mantissas (requires 2x as many bits as input). + /// 2. Normalization of the result (not done here). + /// 3. Addition of exponents. + pub(crate) fn mul(&self, b: &ExtendedFloat) -> ExtendedFloat { + // Logic check, values must be decently normalized prior to multiplication. + debug_assert!((self.mant & u64::HIMASK != 0) && (b.mant & u64::HIMASK != 0)); + + // Extract high-and-low masks. + let ah = self.mant >> u64::HALF; + let al = self.mant & u64::LOMASK; + let bh = b.mant >> u64::HALF; + let bl = b.mant & u64::LOMASK; + + // Get our products + let ah_bl = ah * bl; + let al_bh = al * bh; + let al_bl = al * bl; + let ah_bh = ah * bh; + + let mut tmp = (ah_bl & u64::LOMASK) + (al_bh & u64::LOMASK) + (al_bl >> u64::HALF); + // round up + tmp += 1 << (u64::HALF - 1); + + ExtendedFloat { + mant: ah_bh + (ah_bl >> u64::HALF) + (al_bh >> u64::HALF) + (tmp >> u64::HALF), + exp: self.exp + b.exp + u64::FULL, + } + } + + /// Multiply in-place, as if by `a*b`. + /// + /// The result is not normalized. + #[inline] + pub(crate) fn imul(&mut self, b: &ExtendedFloat) { + *self = self.mul(b); + } + + // NORMALIZE + + /// Normalize float-point number. + /// + /// Shift the mantissa so the number of leading zeros is 0, or the value + /// itself is 0. + /// + /// Get the number of bytes shifted. + #[inline] + pub(crate) fn normalize(&mut self) -> u32 { + // Note: + // Using the cltz intrinsic via leading_zeros is way faster (~10x) + // than shifting 1-bit at a time, via while loop, and also way + // faster (~2x) than an unrolled loop that checks at 32, 16, 4, + // 2, and 1 bit. + // + // Using a modulus of pow2 (which will get optimized to a bitwise + // and with 0x3F or faster) is slightly slower than an if/then, + // however, removing the if/then will likely optimize more branched + // code as it removes conditional logic. + + // Calculate the number of leading zeros, and then zero-out + // any overflowing bits, to avoid shl overflow when self.mant == 0. + let shift = if self.mant == 0 { + 0 + } else { + self.mant.leading_zeros() + }; + shl(self, shift as i32); + shift + } + + // ROUND + + /// Lossy round float-point number to native mantissa boundaries. + #[inline] + pub(crate) fn round_to_native<F, Algorithm>(&mut self, algorithm: Algorithm) + where + F: Float, + Algorithm: FnOnce(&mut ExtendedFloat, i32), + { + round_to_native::<F, _>(self, algorithm); + } + + // FROM + + /// Create extended float from native float. + #[inline] + pub fn from_float<F: Float>(f: F) -> ExtendedFloat { + from_float(f) + } + + // INTO + + /// Convert into default-rounded, lower-precision native float. + #[inline] + pub(crate) fn into_float<F: Float>(mut self) -> F { + self.round_to_native::<F, _>(round_nearest_tie_even); + into_float(self) + } + + /// Convert into downward-rounded, lower-precision native float. + #[inline] + pub(crate) fn into_downward_float<F: Float>(mut self) -> F { + self.round_to_native::<F, _>(round_downward); + into_float(self) + } +} + +// FROM FLOAT + +// Import ExtendedFloat from native float. +#[inline] +pub(crate) fn from_float<F>(f: F) -> ExtendedFloat +where + F: Float, +{ + ExtendedFloat { + mant: u64::as_cast(f.mantissa()), + exp: f.exponent(), + } +} + +// INTO FLOAT + +// Export extended-precision float to native float. +// +// The extended-precision float must be in native float representation, +// with overflow/underflow appropriately handled. +#[inline] +pub(crate) fn into_float<F>(fp: ExtendedFloat) -> F +where + F: Float, +{ + // Export floating-point number. + if fp.mant == 0 || fp.exp < F::DENORMAL_EXPONENT { + // sub-denormal, underflow + F::ZERO + } else if fp.exp >= F::MAX_EXPONENT { + // overflow + F::from_bits(F::INFINITY_BITS) + } else { + // calculate the exp and fraction bits, and return a float from bits. + let exp: u64; + if (fp.exp == F::DENORMAL_EXPONENT) && (fp.mant & F::HIDDEN_BIT_MASK.as_u64()) == 0 { + exp = 0; + } else { + exp = (fp.exp + F::EXPONENT_BIAS) as u64; + } + let exp = exp << F::MANTISSA_SIZE; + let mant = fp.mant & F::MANTISSA_MASK.as_u64(); + F::from_bits(F::Unsigned::as_cast(mant | exp)) + } +} |