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Convert fill values correctly from negative to unsigned integers #165

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Convert fill values correctly from negative to unsigned integers #165

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83016d2
Convert fill values correctly from negative to unsigned integers
asinghvi17 Sep 11, 2024
f931176
Only reinterpret negative integers when decoding fill values to unsigned
asinghvi17 Oct 21, 2024
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9 changes: 9 additions & 0 deletions src/metadata.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -216,5 +216,14 @@ Base.eltype(::Metadata{T}) where T = T
fill_value_decoding(v::AbstractString, T::Type{<:Number}) = parse(T, v)
fill_value_decoding(v::Nothing, ::Any) = v
fill_value_decoding(v, T) = T(v)

fill_value_decoding(v::Number, T::Type{String}) = v == 0 ? "" : T(UInt8[v])
fill_value_decoding(v, ::Type{ASCIIChar}) = v == "" ? nothing : v
# Sometimes when translating between CF (climate and forecast) convention data
# and Zarr groups, fill values are left as "negative integers" to encode unsigned
# integers. So, we have to convert to the signed type with the same number of bytes
# as the unsigned integer, then reinterpret as unsigned. That's how a fill value
# of -1 can have a realistic meaning with an unsigned dtype.
# However, we have to apply this correction only if the integer is negative.
# If it's positive, then the value might be out of range of the signed integer type.
fill_value_decoding(v::Integer, T::Type{<: Unsigned}) = sign(v) < 0 ? reinterpret(T, signed(T)(v)) : T(v)
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