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GH-37730: [C#] throw OverflowException in DecimalUtility if fractionalPart is too large #37731

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merged 7 commits into from
Oct 6, 2023
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GH-37730: [C#] throw OverflowException in DecimalUtility if fractionalPart is too large #37731

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dd4595a
add support for BIGNUMERIC values
Sep 15, 2023
7d8955a
remove unnecessary usings
Sep 15, 2023
8d3237f
update values
Sep 15, 2023
cc89bb1
update wording
Oct 6, 2023
844200b
Merge branch 'apache:main' into dev/large-decimal
davidhcoe Oct 6, 2023
d60bce0
Merge branch 'apache:main' into dev/large-decimal
davidhcoe Oct 6, 2023
a1f7915
update error message
Oct 6, 2023
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6 changes: 5 additions & 1 deletion csharp/src/Apache.Arrow/DecimalUtility.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,11 @@ internal static decimal GetDecimal(in ArrowBuffer valueBuffer, int index, int sc
BigInteger integerPart = BigInteger.DivRem(integerValue, scaleBy, out BigInteger fractionalPart);
if (integerPart > _maxDecimal || integerPart < _minDecimal) // decimal overflow, not much we can do here - C# needs a BigDecimal
{
throw new OverflowException($"Value: {integerPart} too big or too small to be represented as a decimal");
throw new OverflowException($"Value: {integerValue} is too big or too small to be represented as a decimal");
}
if (fractionalPart > _maxDecimal || fractionalPart < _minDecimal) // decimal overflow, not much we can do here - C# needs a BigDecimal
{
throw new OverflowException($"Value: {integerValue} is too big or too small to be represented as a decimal");
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The test cases confused me, but looking at it, it's not necessarily about too big or too small, but rather too precise?

Arrow represents 7.89 in decimal256(76,38) as 789000000000000000000000000000000000000
integerPart is then 7
fractionalPart is 89000000000000000000000000000000000000
and that's just too many digits of precision for decimal?

Which, it is literally too big, but that's a bit confusing unless you are thinking about the representation.

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Separately, I think it would be useful to differentiate the error messages here and possibly include the problematic value

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updated in latest push

}
return (decimal)integerPart + DivideByScale(fractionalPart, scale);
}
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19 changes: 19 additions & 0 deletions csharp/test/Apache.Arrow.Tests/DecimalUtilityTests.cs
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Expand Up @@ -46,6 +46,25 @@ public void HasExpectedResultOrThrows(decimal d, int precision , int scale, bool
Assert.Equal(d, result.GetValue(0));
}
}

[Theory]
[InlineData(4.56, 38, 9, false)]
[InlineData(7.89, 76, 38, true)]
public void Decimal256HasExpectedResultOrThrows(decimal d, int precision, int scale, bool shouldThrow)
{
var builder = new Decimal256Array.Builder(new Decimal256Type(precision, scale));
builder.Append(d);
Decimal256Array result = builder.Build(new TestMemoryAllocator()); ;

if (shouldThrow)
{
Assert.Throws<OverflowException>(() => result.GetValue(0));
}
else
{
Assert.Equal(d, result.GetValue(0));
}
}
}
}
}
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