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Generic frexp #150

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Generic frexp #150

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18 changes: 15 additions & 3 deletions src/math/prearith/prearith.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -41,21 +41,33 @@ end
flipsign(x::DoubleFloat{T}, y::U) where {T<:IEEEFloat, U<:Unsigned} = +x
copysign(x::DoubleFloat{T}, y::U) where {T<:IEEEFloat, U<:Unsigned} = +x

function Base.Math.frexp(x::DoubleFloat{T}) where {T<:IEEEFloat}
"""
frexps(x::DoubleFloat)

Applies `Base.frexp` to both `hi` and `lo` parts, and returns a tuple of tuples.
See also `DoubleFloats.ldexps` for the inverse, and `DoubleFloats.signs` similar tuple.
"""
function frexps(x::DoubleFloat{T}) where {T<:IEEEFloat}
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This is a bit of an awful name, trying to match signs. Could be more explicit like double_frexp or something.

frhi, exphi = frexp(HI(x))
frlo, explo = frexp(LO(x))
return (frhi, exphi), (frlo, explo)
end

function Base.Math.frexp(x::DoubleFloat{T}) where {T<:IEEEFloat}
frhi, exphi = frexp(HI(x))
frlo, explo = frexp(LO(x))
return DoubleFloat{T}(frhi, ldexp(frlo, explo - exphi)), exphi
end

function Base.Math.ldexp(x::DoubleFloat{T}, exponent::I) where {T<:IEEEFloat, I<:Integer}
return DoubleFloat{T}(ldexp(HI(x), exponent), ldexp(LO(x), exponent))
end

function Base.Math.ldexp(dhi::Tuple{T,I}, dlo::Tuple{T,I}) where {T<:IEEEFloat, I<:Integer}
function ldexps(dhi::Tuple{T,I}, dlo::Tuple{T,I}) where {T<:IEEEFloat, I<:Integer}
return DoubleFloat(ldexp(dhi[1], dhi[2]), ldexp(dlo[1], dlo[2]))
end

function Base.Math.ldexp(dhilo::Tuple{Tuple{T,I}, Tuple{T,I}}) where {T<:IEEEFloat, I<:Integer}
function ldexps(dhilo::Tuple{Tuple{T,I}, Tuple{T,I}}) where {T<:IEEEFloat, I<:Integer}
return ldexp(dhilo[1], dhilo[2])
end

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18 changes: 14 additions & 4 deletions test/prearith.jl
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Expand Up @@ -10,12 +10,22 @@
@test flipsign(negval, 1) == negval
@test copysign(val, -1) == negval
@test copysign(negval, 1) == val

@test ldexp(frexp(val)...,) == val
# @test ldexp(significand(val), exponent(val)) == val

@test signs(val) == (sign(HI(val)), sign(LO(val)))
fr, ex = frexp(val)
@test fr * T(2)^ex == val

@test fr ≈ frexp(Float64(val))[1]
@test ex == frexp(Float64(val))[2]

@test isnan(frexp(T(NaN))[1])
@test isinf(frexp(T(Inf))[1])
@test iszero(frexp(T(0))[1])

@test DoubleFloats.ldexps(DoubleFloats.frexps(val)...,) == val
# @test ldexp(significand(val), exponent(val)) == val

@test signs(val) == (sign(HI(val)), sign(LO(val)))
end

@testset "trunc $T" for T in (Double16, Double32, Double64)
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