Translate and explain some C++ bit operations to C#

Can you help me with the translation to c# of this 3rd part API method:

I also didnt understand everything that is happening at the bit operations..

inline void SetBits(unsigned long& aValue,unsigned int aData,unsigned int aPosition,unsigned int aLength)
{
    unsigned int datamask;   // data mask, before aPosition shift

    if (aLength == 32)
        datamask = 0xFFFFFFFF;
    else
        datamask = (1L << aLength) - 1;

    aValue &= ~(datamask << aPosition);             // Clear bits
    aValue |= (aData & datamask) << aPosition;      // Set value
}

Im getting this error in C# version:

Error Operator '<<' cannot be applied to operands of type 'long' and 'uint'

Error Operator '<<' cannot be applied to operands of type 'uint' and 'uint'

EDITED:

I think this solution is ok:

    private void SetBits(ref uint value, uint data开发者_运维问答, int position, int length)
    {
        uint datamask;   // data mask, before position shift

        if (length >= 32)
            datamask = 0xFFFFFFFF;
        else
            datamask = ((uint)1 << length) - 1;

        value &= ~(datamask << position);             // Clear bits
        value |= (data & datamask) << position;      // Set value
    }

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The count part of a shift operation in C# should always be an int. So try making aLength and aPosition into an int instead of a uint. See here.

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As an example to explain the code (in 8-bit, for the sake of simplicity), lets say aValue = 01101001, aData = 00100110, aPosition = 3 and aLength = 4:

datamask = (1L << aLength) - 1;

creates a mask with the aLength (4) rightmost bits set to one: datamask = 00001111.

aValue &= ~(datamask << aPosition);

clears the aLength (4) bits at the aPositionth (3rd) bit position: aValue = 01101001 & 10000111 = 00000001.

aValue |= (aData & datamask) << aPosition;

now copies the aLength (4) rightmost bits of aData to the aPositionth (3rd) bit position in aValue: aValue = 00000001 | 00110000 = 00110001.

So what this function does, is replace the aLength bits at the aPositionth bit position in aValue with the aLength rightmost bits in aData.

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I didnt understand what happens here: datamask = (1L << aLength) - 1;

This code creates a mask with the first (right-most) aLength bits set to 1. The code uses a special rule for aLength=32 because this formula would overflow.