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check for typemin(T) in denominator of rational #32572

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merged 9 commits into from
Dec 17, 2019
Merged

check for typemin(T) in denominator of rational #32572

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c6df5aa
check for `typemin(T)` in denominator of rational
simeonschaub Jul 13, 2019
1b275d7
add test for #32569
simeonschaub Jul 13, 2019
f3dcb6e
check if `typemin` is defined before calling it
simeonschaub Jul 13, 2019
b441119
use `isbitstype` instead of `hasmethod`
simeonschaub Jul 24, 2019
6b299e6
add `hastypemin`, use in Rational constructor
simeonschaub Jul 27, 2019
e0ce76c
`signbit(den) && signbit(-den)` instead of typemin
simeonschaub Nov 25, 2019
418da48
implement suggestions from @KlausC
simeonschaub Nov 29, 2019
afe59bf
remove unnecessary issue number
simeonschaub Nov 30, 2019
52f1bd8
divgcd before typemin check
simeonschaub Dec 12, 2019
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8 changes: 6 additions & 2 deletions base/rational.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -11,12 +11,16 @@ struct Rational{T<:Integer} <: Real
den::T

function Rational{T}(num::Integer, den::Integer) where T<:Integer
num == den == zero(T) && __throw_rational_argerror(T)
num == den == zero(T) && __throw_rational_argerror_zero(T)
if T <: Signed && hasmethod(typemin, Tuple{Type{T}})
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den == typemin(T) && __throw_rational_argerror_typemin(T)
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I'm sorry, in my previous review I was just looking at the typemin stuff, but actually I think this error logic here is not appropriate in general. A type could have a typemin without the current definition being an error. The real problem occurs when typemin(T) == -typemin(T) (which is typically true for bit types which use 2-complement arithmetic). So I suggest instead moving the error checking in the below line, something like: T <: Signed && signbit(den) && signbit(-den) && throw(...).

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Yes, makes sense. So just delete all the hastypemin stuff?

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I don't think, this check is very good, because it requires construction of -den, which is expensive in the case of BigInt.

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It can be constructed only when necessary.

end
num2, den2 = signbit(den) ? divgcd(-num, -den) : divgcd(num, den)
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As @KlausC suggested, this constructs unnecessarily -den once more than necessary. You can rearrange the code to fix that, e.g.

num2, den2 = if signbit(den)
    den = -den
    T <: Signed && signbit(den) && __throw_rational_argerror_typemin(T)
    divgcd(-num, den)
else
    divgcd(num, den)
end

new(num2, den2)
end
end
@noinline __throw_rational_argerror(T) = throw(ArgumentError("invalid rational: zero($T)//zero($T)"))
@noinline __throw_rational_argerror_zero(T) = throw(ArgumentError("invalid rational: zero($T)//zero($T)"))
@noinline __throw_rational_argerror_typemin(T) = throw(ArgumentError("invalid rational: denominator can't be typemin($T)"))

Rational(n::T, d::T) where {T<:Integer} = Rational{T}(n,d)
Rational(n::Integer, d::Integer) = Rational(promote(n,d)...)
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2 changes: 2 additions & 0 deletions test/rational.jl
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Expand Up @@ -32,6 +32,8 @@ using Test
@test_throws ArgumentError rationalize(Int, big(3.0), -1.)
# issue 26823
@test_throws InexactError rationalize(Int, NaN)
# issue 32569
@test_throws ArgumentError 1 // typemin(Int)

for a = -5:5, b = -5:5
if a == b == 0; continue; end
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