extend iseven/isodd to Number #38976
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Sacha0
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Dec 23, 2020
Keno
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Dec 25, 2020
| @@ -122,7 +123,8 @@ julia> iseven(10) | |||
| true | |||
| ``` | |||
| """ | |||
| iseven(n::Integer) = !isodd(n) | |||
| iseven(n::Number) = isreal(n) && iseven(real(n)) | |||
| iseven(n::Real) = isinteger(n) && iszero(rem(Integer(n), 2)) | |||
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Doesn't the cast to Integer here defeat the purpose?
julia> Integer(2.0^65)
ERROR: InexactError: Int64(3.6893488147419103e19)
Stacktrace:
[1] Int64
@ ./float.jl:747 [inlined]
[2] Integer(x::Float64)
@ Core ./boot.jl:789
[3] top-level scope
@ REPL[2]:1
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No, because there is a specialized method for AbstractFloat in float.jl.
This is just the fallback definition, which works for things like Complex{Int} and Rational{Int}.
ElOceanografo
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* extend iseven/isodd to Number * add PR num to NEWS
rfourquet
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This method was depending on the generic implementation `iseven(x::Integer) = !isodd(x)` for its efficiency, but this was removed in #38976, making `iseven(::BigInt)` 30 times slower.
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shirodkara
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This method was depending on the generic implementation `iseven(x::Integer) = !isodd(x)` for its efficiency, but this was removed in JuliaLang#38976, making `iseven(::BigInt)` 30 times slower.
johanmon
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This method was depending on the generic implementation `iseven(x::Integer) = !isodd(x)` for its efficiency, but this was removed in JuliaLang#38976, making `iseven(::BigInt)` 30 times slower.
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Similar to #37635 for
ispow2, it seems like there is no reason to restrict these functions toIntegertypes.I ran into this recently in SpecialFunctions.jl when I was trying to compute something like
(-z)^a Γ(z)bysign * exp(a*log(abs(z)) + logabsgamma(z))forisinteger(a), but whereais not necessarily anIntegertype. In order to compute thesign, I wanted to checkiseven(a), but it didn't work for floating-point types. Andiseven(Int(a))could overflow, so I couldn't use that without an additional guard.