Change return type for T::{log,log2,log10} to u32.

[falk-hueffner]

The value is at most 128, and this is consistent with using u32 for small values elsewhere (e.g. BITS, count_ones, leading_zeros).

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Mark-Simulacrum (or someone else) soon.

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[falk-hueffner]

See also the comment here #70887 (comment)

[scottmcm]

I think this makes good sense to me. u32::log2 for me is just the more useful version of leading_zeros, so having the same return type there seems logical. And I saw that @joshtriplett 👍'd the comment so I'll count that as a libs "seems reasonable" for the change, since this is just unstable anyway.

r? @scottmcm
@bors r+

[bors]

📌 Commit d760c33 has been approved by scottmcm

[bors]

⌛ Testing commit d760c33 with merge b2d9bcd...

[bors]

☀️ Test successful - checks-actions
Approved by: scottmcm
Pushing b2d9bcd to master...

[agausmann]

Super late, but I think it's worth specifically pointing out: this change also agrees with the signature of integer power functions (e.g. u64::pow). All of them use u32 for the exponent argument.

So with this change, this (albeit contrived) expression passes typechecking, if x: u32:
2u64.pow(x).log2() == x