Const rounding methods in float types

language design
1

Some rounding methods in float types (namely trunc, floor, ceil, round, and round_ties_even) could probably be made const, but they currently aren't.

I read Tracking issue for `#![feature(const_fn_floating_point_arithmetic)]` · Issue #57241 · rust-lang/rust · GitHub and many of the issues linked in it, but I did not find a reason for those methods not to be const. For example, abs, min and max became const in Make some float methods unstable `const fn` · rust-lang/rust@c09ed3e · GitHub.

If the answer is simply "because no one took the time to implement that", then I'd like to volunteer.

(I'm sorry if this is the wrong forum to post this - could you please point me to the right place?)

3 Likes
2

For completion, I wrote a few tests that I'd like to see passing here: test: add tests that we expect to pass when float rounding becomes const · ruancomelli/rust@796794b · GitHub.

3

Indeed, that's what it is.

In fact they are all already implemented in Miri:

So that would mostly just have to be moved over to compiler/rustc_const_eval/src/interpret/intrinsics.rs in the compiler.

Definitely feel free to give it a shot. :slight_smile:

2 Likes
4

Thank you very much for the pointer here! I'm very happy to have opened my first PR contributing code to the Rust project: feat: add `const` support for float rounding methods by ruancomelli · Pull Request #141521 · rust-lang/rust · GitHub :tada:

2 Likes