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Tracking issue for extra floating-point logarithm constants #50540

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clarfon opened this issue May 8, 2018 · 9 comments

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@clarfon
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commented May 8, 2018

Specifically, LOG10_2 and LOG2_10. PR: #50539

@clarfon

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commented Nov 27, 2018

Has anyone used these constants at all and want to pitch in for stabilisation of these? These have landed for a while and I'm curious how many people are using them.

@kennytm

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commented Dec 1, 2018

+1 for stabilization. (Tried to see if log2(10) exists and found that it is unstable 🙄.)

@clarfon

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commented Dec 1, 2018

(Mind providing the specific use case? Curious to see if people are using this for anything other than scientific computing.)

@kennytm

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commented Dec 1, 2018

@clarcharr to estimate the "−log2(probability)" of collision of two values chosen randomly from a set, which will be used to derive the probability of collision of N values (≈ 1 − e-pN2/2, p ≪ 1, N ≫ 1).

log2 is chosen instead of natural log because the set size is often 2n (e.g. u32), but sometimes it is drawn from a set of n decimal digits which would then involve n·log2(10).

@iliekturtles

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commented Aug 7, 2019

One hartley is = log2(10) shannons (bits). Currently the constant is duplicated in uom.

@clarfon

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commented Aug 7, 2019

I can't @ anyone from the libs team but do you think we'd be able to start an FCP for this?

@varkor

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commented Sep 28, 2019

@alexcrichton

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commented Sep 30, 2019

@rfcbot fcp merge

I believe the stabilization includes core::{f32, f64}::{LOG2_10, LOG10_2}.

@rfcbot

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commented Sep 30, 2019

Team member @alexcrichton has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

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