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Diffstat (limited to 'vendor/serde_json/src/lexical/algorithm.rs')
| -rw-r--r-- | vendor/serde_json/src/lexical/algorithm.rs | 196 |
1 files changed, 0 insertions, 196 deletions
diff --git a/vendor/serde_json/src/lexical/algorithm.rs b/vendor/serde_json/src/lexical/algorithm.rs deleted file mode 100644 index eaa5e7e..0000000 --- a/vendor/serde_json/src/lexical/algorithm.rs +++ /dev/null @@ -1,196 +0,0 @@ -// Adapted from https://github.com/Alexhuszagh/rust-lexical. - -//! Algorithms to efficiently convert strings to floats. - -use super::bhcomp::*; -use super::cached::*; -use super::errors::*; -use super::float::ExtendedFloat; -use super::num::*; -use super::small_powers::*; - -// FAST -// ---- - -/// Convert mantissa to exact value for a non-base2 power. -/// -/// Returns the resulting float and if the value can be represented exactly. -pub(crate) fn fast_path<F>(mantissa: u64, exponent: i32) -> Option<F> -where - F: Float, -{ - // `mantissa >> (F::MANTISSA_SIZE+1) != 0` effectively checks if the - // value has a no bits above the hidden bit, which is what we want. - let (min_exp, max_exp) = F::exponent_limit(); - let shift_exp = F::mantissa_limit(); - let mantissa_size = F::MANTISSA_SIZE + 1; - if mantissa == 0 { - Some(F::ZERO) - } else if mantissa >> mantissa_size != 0 { - // Would require truncation of the mantissa. - None - } else if exponent == 0 { - // 0 exponent, same as value, exact representation. - let float = F::as_cast(mantissa); - Some(float) - } else if exponent >= min_exp && exponent <= max_exp { - // Value can be exactly represented, return the value. - // Do not use powi, since powi can incrementally introduce - // error. - let float = F::as_cast(mantissa); - Some(float.pow10(exponent)) - } else if exponent >= 0 && exponent <= max_exp + shift_exp { - // Check to see if we have a disguised fast-path, where the - // number of digits in the mantissa is very small, but and - // so digits can be shifted from the exponent to the mantissa. - // https://www.exploringbinary.com/fast-path-decimal-to-floating-point-conversion/ - let small_powers = POW10_64; - let shift = exponent - max_exp; - let power = small_powers[shift as usize]; - - // Compute the product of the power, if it overflows, - // prematurely return early, otherwise, if we didn't overshoot, - // we can get an exact value. - let value = match mantissa.checked_mul(power) { - None => return None, - Some(value) => value, - }; - if value >> mantissa_size != 0 { - None - } else { - // Use powi, since it's correct, and faster on - // the fast-path. - let float = F::as_cast(value); - Some(float.pow10(max_exp)) - } - } else { - // Cannot be exactly represented, exponent too small or too big, - // would require truncation. - None - } -} - -// MODERATE -// -------- - -/// Multiply the floating-point by the exponent. -/// -/// Multiply by pre-calculated powers of the base, modify the extended- -/// float, and return if new value and if the value can be represented -/// accurately. -fn multiply_exponent_extended<F>(fp: &mut ExtendedFloat, exponent: i32, truncated: bool) -> bool -where - F: Float, -{ - let powers = ExtendedFloat::get_powers(); - let exponent = exponent.saturating_add(powers.bias); - let small_index = exponent % powers.step; - let large_index = exponent / powers.step; - if exponent < 0 { - // Guaranteed underflow (assign 0). - fp.mant = 0; - true - } else if large_index as usize >= powers.large.len() { - // Overflow (assign infinity) - fp.mant = 1 << 63; - fp.exp = 0x7FF; - true - } else { - // Within the valid exponent range, multiply by the large and small - // exponents and return the resulting value. - - // Track errors to as a factor of unit in last-precision. - let mut errors: u32 = 0; - if truncated { - errors += u64::error_halfscale(); - } - - // Multiply by the small power. - // Check if we can directly multiply by an integer, if not, - // use extended-precision multiplication. - match fp - .mant - .overflowing_mul(powers.get_small_int(small_index as usize)) - { - // Overflow, multiplication unsuccessful, go slow path. - (_, true) => { - fp.normalize(); - fp.imul(&powers.get_small(small_index as usize)); - errors += u64::error_halfscale(); - } - // No overflow, multiplication successful. - (mant, false) => { - fp.mant = mant; - fp.normalize(); - } - } - - // Multiply by the large power - fp.imul(&powers.get_large(large_index as usize)); - if errors > 0 { - errors += 1; - } - errors += u64::error_halfscale(); - - // Normalize the floating point (and the errors). - let shift = fp.normalize(); - errors <<= shift; - - u64::error_is_accurate::<F>(errors, fp) - } -} - -/// Create a precise native float using an intermediate extended-precision float. -/// -/// Return the float approximation and if the value can be accurately -/// represented with mantissa bits of precision. -#[inline] -pub(crate) fn moderate_path<F>( - mantissa: u64, - exponent: i32, - truncated: bool, -) -> (ExtendedFloat, bool) -where - F: Float, -{ - let mut fp = ExtendedFloat { - mant: mantissa, - exp: 0, - }; - let valid = multiply_exponent_extended::<F>(&mut fp, exponent, truncated); - (fp, valid) -} - -// FALLBACK -// -------- - -/// Fallback path when the fast path does not work. -/// -/// Uses the moderate path, if applicable, otherwise, uses the slow path -/// as required. -pub(crate) fn fallback_path<F>( - integer: &[u8], - fraction: &[u8], - mantissa: u64, - exponent: i32, - mantissa_exponent: i32, - truncated: bool, -) -> F -where - F: Float, -{ - // Moderate path (use an extended 80-bit representation). - let (fp, valid) = moderate_path::<F>(mantissa, mantissa_exponent, truncated); - if valid { - return fp.into_float::<F>(); - } - - // Slow path, fast path didn't work. - let b = fp.into_downward_float::<F>(); - if b.is_special() { - // We have a non-finite number, we get to leave early. - b - } else { - bhcomp(b, integer, fraction, exponent) - } -} |