Tracking Issue for `core_float_math`

[tgross35]

Feature gate: #![feature(core_float_math)]

This is a tracking issue for floating point math operations in core.

Public API

The following API will be made available in core:

impl {f16, f32, f64, f128} {
    pub fn floor(self) -> Self;
    pub fn ceil(self) -> Self;
    pub fn round(self) -> Self;
    pub fn round_ties_even(self) -> Self;
    pub fn trunc(self) -> Self;
    pub fn fract(self) -> Self;
    pub fn mul_add(self, a: Self, b: Self) -> Self;
    pub fn div_euclid(self, rhs: f128) -> Self;
    pub fn rem_euclid(self, rhs: f128) -> Self;
    pub fn powi(self, n: i32) -> Self;
    pub fn sqrt(self) -> Self;
    // Not yet added to f128
    pub fn cbrt(self) -> Self;
    // Deprecated, but there isn't any reason not to move it
    pub fn abs_sub(self, other: Self) -> Self;
}

More will be added in the future. The blocker for others is the quality of our libm implementations (I am working on improving this).

For f32 and f64, it isn't easily possible to have the methods unstable in core but stable in std, so standalone functions are used for the feature gate (e.g. core::f32::sqrt). For stabilization these will be changed to inherent and the duplicates in std removed.

Steps / History

• Background
  • Methods moved from core to std to avoid C libm dependency Remove dependencies on libm functions from libcore. #27823
  • Discussion Tracking issue for f32 and f64 methods in libcore #50145
  • Discussion Math support in core rfcs#2505
  • Trivial methods moved to core float types: move copysign, abs, signum to libcore #131304
• Implementation:
  • Initial implementation Initial implementation of core_float_math #138087
  • Functions moved to a module core_float_math: Move functions to math module #141282
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• [] Not a direct blocker but it would be nice to have a better story about Linking a Rust staticlib unexpectedly changes C math functions from libm to bundled ones from compiler-builtins #142119

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩