Correct fns exp2 that were calling exp

[carols10cents]

Fixes#22080.

I was working on adding examples to the documentation in std::num::Float. I got to exp2, which says "Returns 2 raised to the power of the number, 2^(self)."

So I tried running this code:

use std::num::Float;
#[test]
fn test_exp2() {
assert_eq!(32.0, 5.0.exp2());
}

and it resulted in a failure of (left: 32, right: 148.413159). That 148.413159 is the value for e^5, which is exp(), not exp2().

Sure enough, exp2 is calling exp and shouldn't be, looks like a copy-paste error.

I haven't added any tests for this since it's unlikely to break again, but I will happily do so if people think that would be a good idea. The doc examples are coming :)

I scanned through the other functions in these files for similar sorts of errors and didn't notice any.

[rust-highfive]

r? @aturon

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[huonw]

Nice catch! It seem like all of these functions should have some basic tests to protect against issues like this, a few have such tests (e.g. asinh) but there's a lot missing. Could you add one for exp2 testing a handful of numbers (e.g. extremes like INFINITY, NEG_INFINITY, 0 and one or two "general" values)?

If you're feeling energetic it would be great to add some tests for some of the other functions, but this is definitely not necessary in this patch.

[carols10cents]

@huonw I've added some tests for exp and exp2, I'll probably add tests for the others in another PR. Thank you!!!! 🌻

[mdinger]

Ug. See #22030 which is documenting float. Sounds like you're working on the same thing. Probably don't want to be duplicating each others work...Maybe we should check to see if one has better examples...

[carols10cents]

@mdinger I didn't get too far with the documentation, I stopped when I hit this bug, so you've got better examples for the docs. It's so funny that we both found this within hours!!!

[mdinger]

Agreed. FYI, I'm working from the top down so if you decide to submit a PR against it, start at the bottom and work up. I typically only do a few examples day so it may take a few more days to finish. Then I have to test it.

[huonw]

@bors r+ 8379

Thanks

[bors]

⌛ Testing commit 8379062 with merge 5936278...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-32-nopt-t, auto-win-32-opt, auto-win-64-nopt-t, auto-win-64-opt