Revision control
Copy as Markdown
Other Tools
//! Utilities for Rust numbers.
#![doc(hidden)]
#[cfg(all(not(feature = "std"), feature = "compact"))]
use crate::libm::{powd, powf};
#[cfg(not(feature = "compact"))]
use crate::table::{SMALL_F32_POW10, SMALL_F64_POW10, SMALL_INT_POW10, SMALL_INT_POW5};
#[cfg(not(feature = "compact"))]
use core::hint;
use core::ops;
/// Generic floating-point type, to be used in generic code for parsing.
///
/// Although the trait is part of the public API, the trait provides methods
/// and constants that are effectively non-public: they may be removed
/// at any time without any breaking changes.
pub trait Float:
Sized
+ Copy
+ PartialEq
+ PartialOrd
+ Send
+ Sync
+ ops::Add<Output = Self>
+ ops::AddAssign
+ ops::Div<Output = Self>
+ ops::DivAssign
+ ops::Mul<Output = Self>
+ ops::MulAssign
+ ops::Rem<Output = Self>
+ ops::RemAssign
+ ops::Sub<Output = Self>
+ ops::SubAssign
+ ops::Neg<Output = Self>
{
/// Maximum number of digits that can contribute in the mantissa.
///
/// We can exactly represent a float in radix `b` from radix 2 if
/// `b` is divisible by 2. This function calculates the exact number of
/// digits required to exactly represent that float.
///
/// According to the "Handbook of Floating Point Arithmetic",
/// for IEEE754, with emin being the min exponent, p2 being the
/// precision, and b being the radix, the number of digits follows as:
///
/// `−emin + p2 + ⌊(emin + 1) log(2, b) − log(1 − 2^(−p2), b)⌋`
///
/// For f32, this follows as:
/// emin = -126
/// p2 = 24
///
/// For f64, this follows as:
/// emin = -1022
/// p2 = 53
///
/// In Python:
/// `-emin + p2 + math.floor((emin+1)*math.log(2, b) - math.log(1-2**(-p2), b))`
///
/// This was used to calculate the maximum number of digits for [2, 36].
const MAX_DIGITS: usize;
// MASKS
/// Bitmask for the sign bit.
const SIGN_MASK: u64;
/// Bitmask for the exponent, including the hidden bit.
const EXPONENT_MASK: u64;
/// Bitmask for the hidden bit in exponent, which is an implicit 1 in the fraction.
const HIDDEN_BIT_MASK: u64;
/// Bitmask for the mantissa (fraction), excluding the hidden bit.
const MANTISSA_MASK: u64;
// PROPERTIES
/// Size of the significand (mantissa) without hidden bit.
const MANTISSA_SIZE: i32;
/// Bias of the exponet
const EXPONENT_BIAS: i32;
/// Exponent portion of a denormal float.
const DENORMAL_EXPONENT: i32;
/// Maximum exponent value in float.
const MAX_EXPONENT: i32;
// ROUNDING
/// Mask to determine if a full-carry occurred (1 in bit above hidden bit).
const CARRY_MASK: u64;
/// Bias for marking an invalid extended float.
// Value is `i16::MIN`, using hard-coded constants for older Rustc versions.
const INVALID_FP: i32 = -0x8000;
// Maximum mantissa for the fast-path (`1 << 53` for f64).
const MAX_MANTISSA_FAST_PATH: u64 = 2_u64 << Self::MANTISSA_SIZE;
// Largest exponent value `(1 << EXP_BITS) - 1`.
const INFINITE_POWER: i32 = Self::MAX_EXPONENT + Self::EXPONENT_BIAS;
// Round-to-even only happens for negative values of q
// when q ≥ −4 in the 64-bit case and when q ≥ −17 in
// the 32-bitcase.
//
// When q ≥ 0,we have that 5^q ≤ 2m+1. In the 64-bit case,we
// have 5^q ≤ 2m+1 ≤ 2^54 or q ≤ 23. In the 32-bit case,we have
// 5^q ≤ 2m+1 ≤ 2^25 or q ≤ 10.
//
// When q < 0, we have w ≥ (2m+1)×5^−q. We must have that w < 2^64
// so (2m+1)×5^−q < 2^64. We have that 2m+1 > 2^53 (64-bit case)
// or 2m+1 > 2^24 (32-bit case). Hence,we must have 2^53×5^−q < 2^64
// (64-bit) and 2^24×5^−q < 2^64 (32-bit). Hence we have 5^−q < 2^11
// or q ≥ −4 (64-bit case) and 5^−q < 2^40 or q ≥ −17 (32-bitcase).
//
// Thus we have that we only need to round ties to even when
// we have that q ∈ [−4,23](in the 64-bit case) or q∈[−17,10]
// (in the 32-bit case). In both cases,the power of five(5^|q|)
// fits in a 64-bit word.
const MIN_EXPONENT_ROUND_TO_EVEN: i32;
const MAX_EXPONENT_ROUND_TO_EVEN: i32;
/// Minimum normal exponent value `-(1 << (EXPONENT_SIZE - 1)) + 1`.
const MINIMUM_EXPONENT: i32;
/// Smallest decimal exponent for a non-zero value.
const SMALLEST_POWER_OF_TEN: i32;
/// Largest decimal exponent for a non-infinite value.
const LARGEST_POWER_OF_TEN: i32;
/// Minimum exponent that for a fast path case, or `-⌊(MANTISSA_SIZE+1)/log2(10)⌋`
const MIN_EXPONENT_FAST_PATH: i32;
/// Maximum exponent that for a fast path case, or `⌊(MANTISSA_SIZE+1)/log2(5)⌋`
const MAX_EXPONENT_FAST_PATH: i32;
/// Maximum exponent that can be represented for a disguised-fast path case.
/// This is `MAX_EXPONENT_FAST_PATH + ⌊(MANTISSA_SIZE+1)/log2(10)⌋`
const MAX_EXPONENT_DISGUISED_FAST_PATH: i32;
/// Convert 64-bit integer to float.
fn from_u64(u: u64) -> Self;
// Re-exported methods from std.
fn from_bits(u: u64) -> Self;
fn to_bits(self) -> u64;
/// Get a small power-of-radix for fast-path multiplication.
///
/// # Safety
///
/// Safe as long as the exponent is smaller than the table size.
unsafe fn pow_fast_path(exponent: usize) -> Self;
/// Get a small, integral power-of-radix for fast-path multiplication.
///
/// # Safety
///
/// Safe as long as the exponent is smaller than the table size.
#[inline(always)]
unsafe fn int_pow_fast_path(exponent: usize, radix: u32) -> u64 {
// SAFETY: safe as long as the exponent is smaller than the radix table.
#[cfg(not(feature = "compact"))]
return match radix {
5 => unsafe { *SMALL_INT_POW5.get_unchecked(exponent) },
10 => unsafe { *SMALL_INT_POW10.get_unchecked(exponent) },
_ => unsafe { hint::unreachable_unchecked() },
};
#[cfg(feature = "compact")]
return (radix as u64).pow(exponent as u32);
}
/// Returns true if the float is a denormal.
#[inline]
fn is_denormal(self) -> bool {
self.to_bits() & Self::EXPONENT_MASK == 0
}
/// Get exponent component from the float.
#[inline]
fn exponent(self) -> i32 {
if self.is_denormal() {
return Self::DENORMAL_EXPONENT;
}
let bits = self.to_bits();
let biased_e: i32 = ((bits & Self::EXPONENT_MASK) >> Self::MANTISSA_SIZE) as i32;
biased_e - Self::EXPONENT_BIAS
}
/// Get mantissa (significand) component from float.
#[inline]
fn mantissa(self) -> u64 {
let bits = self.to_bits();
let s = bits & Self::MANTISSA_MASK;
if !self.is_denormal() {
s + Self::HIDDEN_BIT_MASK
} else {
s
}
}
}
impl Float for f32 {
const MAX_DIGITS: usize = 114;
const SIGN_MASK: u64 = 0x80000000;
const EXPONENT_MASK: u64 = 0x7F800000;
const HIDDEN_BIT_MASK: u64 = 0x00800000;
const MANTISSA_MASK: u64 = 0x007FFFFF;
const MANTISSA_SIZE: i32 = 23;
const EXPONENT_BIAS: i32 = 127 + Self::MANTISSA_SIZE;
const DENORMAL_EXPONENT: i32 = 1 - Self::EXPONENT_BIAS;
const MAX_EXPONENT: i32 = 0xFF - Self::EXPONENT_BIAS;
const CARRY_MASK: u64 = 0x1000000;
const MIN_EXPONENT_ROUND_TO_EVEN: i32 = -17;
const MAX_EXPONENT_ROUND_TO_EVEN: i32 = 10;
const MINIMUM_EXPONENT: i32 = -127;
const SMALLEST_POWER_OF_TEN: i32 = -65;
const LARGEST_POWER_OF_TEN: i32 = 38;
const MIN_EXPONENT_FAST_PATH: i32 = -10;
const MAX_EXPONENT_FAST_PATH: i32 = 10;
const MAX_EXPONENT_DISGUISED_FAST_PATH: i32 = 17;
#[inline(always)]
unsafe fn pow_fast_path(exponent: usize) -> Self {
// SAFETY: safe as long as the exponent is smaller than the radix table.
#[cfg(not(feature = "compact"))]
return unsafe { *SMALL_F32_POW10.get_unchecked(exponent) };
#[cfg(feature = "compact")]
return powf(10.0f32, exponent as f32);
}
#[inline]
fn from_u64(u: u64) -> f32 {
u as _
}
#[inline]
fn from_bits(u: u64) -> f32 {
// Constant is `u32::MAX` for older Rustc versions.
debug_assert!(u <= 0xffff_ffff);
f32::from_bits(u as u32)
}
#[inline]
fn to_bits(self) -> u64 {
f32::to_bits(self) as u64
}
}
impl Float for f64 {
const MAX_DIGITS: usize = 769;
const SIGN_MASK: u64 = 0x8000000000000000;
const EXPONENT_MASK: u64 = 0x7FF0000000000000;
const HIDDEN_BIT_MASK: u64 = 0x0010000000000000;
const MANTISSA_MASK: u64 = 0x000FFFFFFFFFFFFF;
const MANTISSA_SIZE: i32 = 52;
const EXPONENT_BIAS: i32 = 1023 + Self::MANTISSA_SIZE;
const DENORMAL_EXPONENT: i32 = 1 - Self::EXPONENT_BIAS;
const MAX_EXPONENT: i32 = 0x7FF - Self::EXPONENT_BIAS;
const CARRY_MASK: u64 = 0x20000000000000;
const MIN_EXPONENT_ROUND_TO_EVEN: i32 = -4;
const MAX_EXPONENT_ROUND_TO_EVEN: i32 = 23;
const MINIMUM_EXPONENT: i32 = -1023;
const SMALLEST_POWER_OF_TEN: i32 = -342;
const LARGEST_POWER_OF_TEN: i32 = 308;
const MIN_EXPONENT_FAST_PATH: i32 = -22;
const MAX_EXPONENT_FAST_PATH: i32 = 22;
const MAX_EXPONENT_DISGUISED_FAST_PATH: i32 = 37;
#[inline(always)]
unsafe fn pow_fast_path(exponent: usize) -> Self {
// SAFETY: safe as long as the exponent is smaller than the radix table.
#[cfg(not(feature = "compact"))]
return unsafe { *SMALL_F64_POW10.get_unchecked(exponent) };
#[cfg(feature = "compact")]
return powd(10.0f64, exponent as f64);
}
#[inline]
fn from_u64(u: u64) -> f64 {
u as _
}
#[inline]
fn from_bits(u: u64) -> f64 {
f64::from_bits(u)
}
#[inline]
fn to_bits(self) -> u64 {
f64::to_bits(self)
}
}
#[inline(always)]
#[cfg(all(feature = "std", feature = "compact"))]
pub fn powf(x: f32, y: f32) -> f32 {
x.powf(y)
}
#[inline(always)]
#[cfg(all(feature = "std", feature = "compact"))]
pub fn powd(x: f64, y: f64) -> f64 {
x.powf(y)
}