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math: Modf error with negative zero #12867

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ssilverman opened this issue Oct 7, 2015 · 4 comments
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math: Modf error with negative zero #12867

ssilverman opened this issue Oct 7, 2015 · 4 comments
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Go1.6

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@ssilverman
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Since math.Modf(-0.333) produces -0 and -0.333, shouldn't calling math.Modf on negative zero produce -0 and -0?

Example code:
http://play.golang.org/p/pJMBWAXiYa

I create negative zero via: 1 / math.Inf(-1)
@ianlancetaylor ianlancetaylor changed the title math.Modf error with negative zero math: Modf error with negative zero Oct 7, 2015
@ianlancetaylor ianlancetaylor added this to the Go1.6 milestone Oct 7, 2015
@griesemer
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I think it's a bug. The result is 0, -0 which doesn't add up to -0 as it should.

(FYI, you can create a -0 more easily: http://play.golang.org/p/KTgiTOAZl0)

@griesemer griesemer self-assigned this Oct 7, 2015
@cldorian
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cldorian commented Oct 7, 2015

@griesemer, I can fix this if you wish. The remaining problem I have is that the x87 version returns -0, 0 rather than -0, -0, so it will need to either be fixed or discarded.

@griesemer
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@cldorian please go ahead, thanks!

@gopherbot
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CL https://golang.org/cl/15570 mentions this issue.

@golang golang locked and limited conversation to collaborators Oct 9, 2016
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@ssilverman @ianlancetaylor @griesemer @gopherbot @cldorian