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Fix Random.Next returns negative numbers #405 #840

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Sep 5, 2018
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Fix Random.Next returns negative numbers #405 #840

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2 changes: 1 addition & 1 deletion src/CLR/CorLib/corlib_native_System_Random.cpp
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Expand Up @@ -14,7 +14,7 @@ HRESULT Library_corlib_native_System_Random::Next___I4( CLR_RT_StackFrame& stack

NANOCLR_CHECK_HRESULT(GetRandom( stack, rand ));

stack.SetResult_I4( rand->Next() );
stack.SetResult_I4( rand->Next() & 0x7FFFFFFF );
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Isn't simply casting a less "expensive" operation as it just gets compiled without requiring any extra operations (ANDing with 0x7FFFFFFF)?

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No. Casting for instance 0xFFFFFFFF which is a valid return value from rand->Next() into an int32 results in the value -1. So I think we need ANDing or modulo operation like % 0x7FFFFFFF

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OK! so we have a winner! 👍

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@doingnz doingnz Sep 5, 2018 •
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Personally I am inclined to avoid "magic values" in code. Maybe in the future we could use & Int32.MaxValue which is equivalent to the implemented & 0x7FFFFFFF as it helps the source code to be "self documenting" as to why the specific mask is being applied.

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@doingnz I don't know if we have access to Int32.MaxValue

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I agree with @doingnz .
There is a constant in the CRT lib with that value...
Or maybe a comment explaining why that is being done is good enough.


NANOCLR_NOCLEANUP();
}
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