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Implement LowerExp and UpperExp for integers #39479

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clarfonthey opened this issue Feb 3, 2017 · 5 comments
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Implement LowerExp and UpperExp for integers #39479

clarfonthey opened this issue Feb 3, 2017 · 5 comments
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C-feature-accepted Category: A feature request that has been accepted pending implementation. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@clarfonthey
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clarfonthey commented Feb 3, 2017 •
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I'd be willing to work on this at some point, but I figured that I'd offer this as a feature request in case someone else is interested.

It's very useful to be able to print large integers in scientific notation to get a glance at what order of magnitude they are. For example, seeing 1e10 is much easier to comprehend than 10000000000.
@clarfonthey clarfonthey mentioned this issue Feb 3, 2017
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@phungleson
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Thanks @clarcharr, looks interesting and simple enough for me.

I can look into this.

@phungleson
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@clarcharr seems like the implementation for f32 and f64 is around this function

rust/src/libcore/fmt/mod.rs

Line 1539 in 86d9ed6

fn float_to_exponential_common<T>(fmt: &mut Formatter, num: &T, upper: bool) -> Result

Do you think we can just reuse it?

@hanna-kruppe
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hanna-kruppe commented Feb 6, 2017 •
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That code is strongly tied to floats. I don't believe it can be reused for (64- and 128-bit) integers at all, but even if, it would probably be much more painful than just writing a clean-room implementation tailored to integers.

@Mark-Simulacrum Mark-Simulacrum added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label May 20, 2017
@Mark-Simulacrum Mark-Simulacrum added the C-feature-request Category: A feature request, i.e: not implemented / a PR. label Jul 27, 2017
@dtolnay dtolnay added C-feature-accepted Category: A feature request that has been accepted pending implementation. and removed C-feature-request Category: A feature request, i.e: not implemented / a PR. labels Nov 18, 2017
@dtolnay
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dtolnay commented Nov 18, 2017

I agree that a separate implementation for integers would be easier than trying to use the float one. I would love a PR to add these impls!

@maxbla maxbla mentioned this issue Nov 24, 2019
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Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this issue Feb 15, 2020
@Dylan-DPC
Rollup merge of rust-lang#66721 - maxbla:exp-format-integers, r=KodrAus
afea30d 
implement LowerExp and UpperExp for integers

Addresses rust-lang#39479

This implementation is heavily based on the preexisting `macro_rules! impl_Display` in the same file. I don't like the liberal use of unsafe in that macro and would like to modify it so `unsafe` is only present where necessary. What is Rust's policy on doing such modifications?

Also, I couldn't figure out where to put tests, can I have some help with that?
@maxbla
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maxbla commented Mar 12, 2020

I fixed this with #66721, but this issue wasn't automatically closed

@dtolnay dtolnay closed this as completed Mar 12, 2020
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@phungleson @dtolnay @hanna-kruppe @Mark-Simulacrum @maxbla @clarfonthey