Decimal.Multiply precision failing at decimal places between 4294.000000 and 4295.000000 for two decimal types multiplication

[sachincholkar]

Type of issue

Code doesn't work

Description

//Code result = 0 decimal price = 0m; decimal valUnits = 4295.000000m; Console.WriteLine(Decimal.Multiply(price, valUnits));

//Code result = 0.000000 decimal price = 0m; decimal valUnits = 4294.000000m; Console.WriteLine(Decimal.Multiply(price, valUnits));

//Code result = 0.000000 decimal price = 0m; decimal valUnits = 4295.00000m; //reduced decimal places to 5 Console.WriteLine(Decimal.Multiply(price, valUnits));

when working with decimal types, expectation is for result decimal to preserve the decimal zeros. Even if the result is 0, then it should be common for all the results. Between 4294.000000 & 4295.000000, the binary values don't change significantly except for the lowest bit.

Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.decimal.multiply?view=net-8.0#system-decimal-multiply(system-decimal-system-decimal)

Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System/Decimal.xml

Document Version Independent Id

4ec1f71e-31ee-e91a-5126-48b16ef44812

Article author

@dotnet-bot

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[tannergooding]

This is how its always behaved and it matches how the underlying Win32 DECIMAL type on which this is based behaves as well.

[tannergooding]

In general you can compare the decimal behavior with the underlying VarDec* function (VarDecMul in this case) and we are expected to match that behavior.

In this case, the underlying native implementation does not preserve trailing zeros in all cases and there is, AFAIK, no guarantee of that in any documentation. The managed implementation of this function is here: https://source.dot.net/#System.Private.CoreLib/src/libraries/System.Private.CoreLib/src/System/Decimal.DecCalc.cs,04f3e28ca99259ec

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