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Complex +-0. #4748

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vicuna opened this issue Mar 18, 2009 · 1 comment
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Complex +-0. #4748

vicuna opened this issue Mar 18, 2009 · 1 comment
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bug stdlib suspended

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@vicuna
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vicuna commented Mar 18, 2009

Original bug ID: 4748
Reporter: @Chris00
Status: resolved (set by @xavierleroy on 2013-07-19T09:40:54Z)
Resolution: suspended
Priority: normal
Severity: minor
Version: 3.11.0
Category: standard library
Related to: #8267
Monitored by: @Chris00

Bug description

This is related to bug #1817 albeit not fitting the description, thus I open a new issue.

Complex.mul Complex.one {Complex.re=(-1.); Complex.im = 0.0};;

  • : Complex.t = {Complex.re = -1.; Complex.im = 0.}

Complex.div Complex.one {Complex.re=(-1.); Complex.im = 0.0};;

  • : Complex.t = {Complex.re = -1.; Complex.im = -0.}

(note the sign of the imaginary part). I believe the second is correct while the first one should return {Complex.re = -1.; Complex.im = -0.}.
@vicuna
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vicuna commented Jul 19, 2013

Comment author: @xavierleroy

I welcome pointers to a good tutorial on complex arithmetic using IEEE754 floats.

I can understand why you'd expect im = -0.0 in the first example, yet the "_Cmultd" reference implementation of complex multiply in ISO C99, annex G, gives im = +0.0...

Suspending this PR until we have solid background on complex IEEE754 arithmetic.

@vicuna vicuna closed this as completed Jul 19, 2013
@vicuna vicuna mentioned this issue Mar 14, 2019
Closed
@vicuna vicuna added the bug label Mar 20, 2019
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