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Debug impl of floating numbers does not display signaling NaNs #24624

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nagisa opened this issue Apr 20, 2015 · 2 comments
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Debug impl of floating numbers does not display signaling NaNs #24624

nagisa opened this issue Apr 20, 2015 · 2 comments
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C-feature-request Category: A feature request, i.e: not implemented / a PR. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@nagisa
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nagisa commented Apr 20, 2015 

use std::mem;

fn main() {
    let signaling_nan: f32 = unsafe {mem::transmute(0x7FC0_0000u32)};
    assert_eq!(format!("{:?}", signaling_nan), "sNaN(00000)");
}

fails with “assertion failed: (left == right) (left: "NaN", right: "sNaN(00000)")”

The actual representation is bikeshedable (could be just “sNaN” etc).

playpen
@rprichard rprichard mentioned this issue Apr 20, 2015
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@steveklabnik
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steveklabnik commented Jun 27, 2016 •
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Triage: no change

@steveklabnik steveklabnik added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. and removed A-libs labels Mar 24, 2017
@Mark-Simulacrum Mark-Simulacrum added the C-feature-request Category: A feature request, i.e: not implemented / a PR. label Jul 22, 2017
@dtolnay
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dtolnay commented Nov 17, 2017

This seems okay but I would prefer to see an RFC to justify this a little better. In particular:

  • What use cases is this intended to solve?
  • How do some other languages solve those use cases?
  • Does Debug of a quiet NaN also need to tell us which of the many quiet NaNs it is?
  • (less important) Brainstorm some alternative representations.

@dtolnay dtolnay closed this as completed Nov 17, 2017
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@steveklabnik @nagisa @dtolnay @Mark-Simulacrum