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Support arbitrary AbstractIrrationals #116

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Support arbitrary AbstractIrrationals #116

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2 changes: 1 addition & 1 deletion src/Quadmath.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -465,7 +465,7 @@ end

Float128(::Irrational{:π}) = reinterpret(Float128, 0x4000921fb54442d18469898cc51701b8)
Float128(::Irrational{:ℯ}) = reinterpret(Float128, 0x40005bf0a8b1457695355fb8ac404e7a)
Float128(x::Irrational{T}) where {T} = Float128(BigFloat(x))
Float128(x::AbstractIrrational) = Float128(BigFloat(x))

@stevengj stevengj Sep 26, 2026 •
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Shouldn't we specify the precision here? (The default BigFloat precision of 256 is more than what is required, but the user might have called setprecision to a lower precision.)

Suggested change
Float128(x::AbstractIrrational) = Float128(BigFloat(x))
Float128(x::AbstractIrrational) = Float128(BigFloat(x, precision=128))

(technically I guess you could use precision=113, but it seems sensible to have a few guard bits and I doubt there is much of a performance price to round up to the next power of 2)


import Base.MPFR

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7 changes: 7 additions & 0 deletions test/runtests.jl
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Expand Up @@ -202,11 +202,18 @@ end
@test parse(Float128,"3.0") == Float128(3.0)
end

struct TwoPi <: AbstractIrrational
end
Base.BigFloat(::TwoPi; precision=precision(BigFloat)) =
setprecision(() -> 2 * big(π), BigFloat, precision)
Base.Float64(x::TwoPi) = Float64(big(x))

@testset "irrationals" begin
tiny = 2eps(Float128(1))
@test abs(cos(Float128(pi)) + 1) < tiny
@test abs(log(Float128(ℯ)) - 1) < tiny
@test abs((2*Float128(MathConstants.golden) - 1)^2 - 5) < 5 * tiny
@test abs(cos(Float128(TwoPi())) - 1) < tiny

@stevengj stevengj Sep 26, 2026

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Would be good to test the above issue by surrounding the tests with setprecision(16) do ... end

end

@testset "rationals" begin
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