Pure 32-bit versions of 32-bit math functions

[matthuszagh]

Pure 32-bit versions of 32-bit math functions

[Lokathor]

• We should absolutely have high quality pure 32-bit impls available within rust.
• They could be "the" impl of each libm function on 32-bit CPUs (or whatever criteria) via cfg, or all the time, without having to start a new crate.
• As long as the implementation is correct, the origin of the impl doesn't seem important.

So, yeah, option 2 seems best.

[CryZe]

target_pointer_width tells you nothing about whether f64 is natively supported or not.

[nickmertin]

Has there been any movement on this?

[burrbull]

Don't forget that we have target attributes: #[cfg(target_pointer_width = "64")]

[alexcrichton]

I would personally think that actually having both the 64-bit emulation as well as the 32-bit implementation is a viable option. I would imagine that implementing the 32-bit operation in terms of the 64-bit operation improves code-size if you use both, which might be important for some situations (?).

Additionally I would expected that any 32-bit-specific version would be thoroughly tested, so the maintenance burden doesn't seem like it would be especially high to have two versions (assuming the 32-bit version is a trivial wrapper around the 64-bit version).

The important bit here though I think is the 32-bit-specific CI. I think we'd need a target on CI that verifies that 64-bit things weren't used in the implementation, but I'm not sure how to write that CI myself.

[burrbull]

We can use 64-bit version for 64-bit systems and have cargo option like force-i32 for special use cases.