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rational powers (fixes #18114) #18118

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Aug 19, 2016
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rational powers (fixes #18114) #18118

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rational powers (fixes #18114)
pwl Aug 18, 2016
eef0c45
Update numbers.jl
pwl Aug 18, 2016
d7a1cf3
Update rational.jl
pwl Aug 19, 2016
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4 changes: 2 additions & 2 deletions base/rational.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -375,8 +375,8 @@ function ^(x::Rational, n::Integer)
end

^(x::Number, y::Rational) = x^(y.num/y.den)
^{T<:AbstractFloat}(x::T, y::Rational) = x^(convert(T, y.num / y.den))
^{T<:AbstractFloat}(x::Complex{T}, y::Rational) = x^(convert(T, y.num / y.den))
^{T<:AbstractFloat}(x::T, y::Rational) = x^convert(T,y)
^{T<:AbstractFloat}(x::Complex{T}, y::Rational) = x^convert(T,y)

^{T<:Rational}(z::Complex{T}, n::Bool) = n ? z : one(z) # to resolve ambiguity
function ^{T<:Rational}(z::Complex{T}, n::Integer)
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3 changes: 2 additions & 1 deletion test/numbers.jl
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Expand Up @@ -2137,7 +2137,8 @@ rationalize(nextfloat(0.0)) == 0//1
# rational-exponent promotion rules (issue #3155):
@test 2.0f0^(1//3) == 2.0f0^(1.0f0/3)
@test 2^(1//3) == 2^(1/3)

# no loss of precision for rational powers (issue #18114)
@test BigFloat(2)^(BigFloat(1)/BigFloat(3)) == BigFloat(2)^(1//3)
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Not a big deal, but you can use cbrt(BigFloat(2)) on the left-hand side

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@stevengj stevengj Aug 18, 2016 •
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Not if we want to guarantee exact equality, since cbrt might eventually do something fancy.

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It already does for BigFloat, which calls mpfr_cbrt.


# large shift amounts
@test Int32(-1)>>31 == -1
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