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sign((-1)//typemin(Int)) != sign(typemin(Int)//(-1)) #32443

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JeffreySarnoff opened this issue Jun 27, 2019 · 4 comments · Fixed by #51085
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sign((-1)//typemin(Int)) != sign(typemin(Int)//(-1)) #32443

JeffreySarnoff opened this issue Jun 27, 2019 · 4 comments · Fixed by #51085
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domain:rationals The Rational type and values thereof

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@JeffreySarnoff
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JeffreySarnoff commented Jun 27, 2019 •
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julia> sign(typemin(Int)//(-1))
-1//1
julia> sign((-1)//typemin(Int))
1//1

and also for the other Signed bitstypes and also for signbit.
@JeffreySarnoff JeffreySarnoff changed the title sign((-1)//typemin(Int)) != sign(typemin(Int)//(-1)) sign((-1)//typemin(Int)) != sign(typemin(Int)//(-1)) Jun 27, 2019
@Moelf
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Moelf commented Jun 28, 2019

problems seems to be:

julia> ((-1)//typemin(Int)).num
1

julia> (typemin(Int)//(-1)).num
-9223372036854775808

@musm
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musm commented Jun 28, 2019

This is because
typemin(Int) == -typemin(Int) # true

@JeffreySarnoff
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one(T)//typemin(T), typemin(T)//one(T) are legit
(-one(T))//typemin(T), typemin(T)//(-one(T)) are not because there is no value in T == |typemin(T)|
we trap Rational overflow rather than autowiden, yet this is not trapped

@JeffBezanson JeffBezanson added the domain:rationals The Rational type and values thereof label Jul 1, 2019
@Liozou
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Liozou commented Apr 12, 2020

Fixed by #32572?

@nhz2 nhz2 mentioned this issue Aug 28, 2023
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oscardssmith pushed a commit that referenced this issue Oct 21, 2023
@nhz2
Throw OverflowError on typemin(Int)//(-1) (#51085)
fb01dd2 
Fixes #32443

Currently `typemin(Int)//(-1) == typemin(Int)//(1)`, ignoring an
overflow.

As noted by @JeffreySarnoff in
[#32443](#32443 (comment))
This should throw an error instead of silently overflowing.

To fix this I am using `checked_neg` instead of `-` in the Rational
constructor.

With this PR `(-one(T))//typemin(T)` will now also throw an
`OverflowError` instead of an `ArgumentError`
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Throw OverflowError on typemin(Int)//(-1) nhz2/julia
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@JeffBezanson @JeffreySarnoff @musm @Moelf @Liozou