Tracking Issue for #![feature(const_float_round_methods)]

[ruancomelli]

Feature gate: #![feature(const_float_round_methods)]

This is a tracking issue for making const some methods of floating point types:

• f64::{floor, ceil, trunc, fract, round, round_ties_even}
• and the corresponding methods for f16, f32 and f128

This extends the work done in #130843

Public API

// in `core`
impl <float> {
    // ...
    pub const fn floor(self) -> Self;
    pub const fn ceil(self) -> Self;
    pub const fn trunc(self) -> Self;
    pub const fn fract(self) -> Self;
    pub const fn round(self) -> Self;
    pub const fn round_ties_even(self) -> Self;
    // ...
}

Steps / History

• Opened a discussion topic on the internals forum: Const rounding methods in float types
  • Since all the required machinery was already implemented in the Miri, the implementation was straightforward.
• Implementation: Add const support for float rounding methods #141521
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Should the rounding methods on f16 and f128 be gated behind #[rustc_const_unstable(feature = {"f16", "f128"}, issue = "116909")] (from Tracking Issue for f16 and f128 float types #116909) or #[rustc_const_unstable(feature = "const_float_round_methods", issue = "<this one>")]? The answer is both! Check out this comment: Add const support for float rounding methods #141521 (comment).

Footnotes

Footnotes

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