make sign preserve type

Author: araujoms

src/math/prearith/prearith.jl

@@ -1,5 +1,5 @@
 @inline signbit(a::DoubleFloat{T}) where {T} = signbit(HI(a))
-@inline sign(a::DoubleFloat{T}) where {T} = sign(HI(a))
+@inline sign(a::DoubleFloat{T}) where {T} = DoubleFloat{T}(sign(HI(a)))
 
 @inline function (-)(a::DoubleFloat{T}) where {T<:IEEEFloat}
     if iszero(LO(a)) || isnan(LO(a))

test/prearith.jl

@@ -26,6 +26,8 @@
     # @test ldexp(significand(val), exponent(val)) == val
 
     @test signs(val) == (sign(HI(val)), sign(LO(val)))
+    @test sign(val) === T(1)
+    @test sign(negval) === T(-1)
 end
 
 @testset "trunc $T" for T in (Double16, Double32, Double64)