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Don't convert to Float64 in Printf #180

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Don't convert to Float64 in Printf #180

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2 changes: 2 additions & 0 deletions src/DecFP.jl
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Expand Up @@ -807,6 +807,8 @@ promote_rule(::Type{Irrational{s}}, T::Type{Complex{F}}) where {s,F<:DecimalFloa
Base.widen(::Type{Dec32}) = Dec64
Base.widen(::Type{Dec64}) = Dec128

Printf.tofloat(x::DecimalFloatingPoint) = BigFloat(x)
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Don't we need to pass a precision? Otherwise the BigFloat constructor may use too low a precision.

Why do we need a conversion at all here? Wouldn't it be possible to have Printf.tofloat(x::DecimalFloatingPoint) = x and support printing natively on decimal floating point values? It seems like a shame to do a lossy conversion to binary floating point for printing — kinda defeats the point.

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I would also prefer to not go through BigFloat. In the original Printf PR, there is another interface mentioned where we could pass a buffer of digit chars and the location of the decimal point and have that formatted.
I would like to try that interface but I can't find it in the current code. JuliaLang/julia#32859 (comment) Is that interface implemented @quinnj ?


macro d_str(s, flags...) parse(Dec64, s) end
macro d32_str(s, flags...) parse(Dec32, s) end
macro d64_str(s, flags...) parse(Dec64, s) end
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3 changes: 3 additions & 0 deletions test/runtests.jl
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Expand Up @@ -184,6 +184,9 @@ for T in (Dec32, Dec64, Dec128)

@test @sprintf("%.2f %.4f", T("12.34567"), 9.87) == "12.35 9.8700"

# issue #178
@test @sprintf("%.36f", T("0.1")) == "0.100000000000000000000000000000000000"

x,y,z = 1.5, -3.25, 0.0625 # exactly represented in binary
xd = T(x); yd = T(y); zd = T(z)

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