DirectX Compute and thread addressing

Hi

I have been working through the DirectCompute PDC HOL tutorials. The last example - the Game of Life was particulary relevant as I would like to implement a GPGPU version of a reaction- diffusion system in 3D. In the Game of Life periodic boundary conditions are assumed and I can see how the thread addressing can be manipulated to achieve this - see below extracted from the tutorial.

For my implementation I would need Von Neumann (reflective/no flux) boundary conditions. I am at a loss as how to implement this or change the code below to go from periodic to reflective boundaries. Any advice would be much appreciated,

Thanks in advance... 

//--------------------------------------------------------------------------------------

// threadIDToCell

// given a thread DTid and group Gid, calculate the corresponding cell position

//--------------------------------------------------------------------------------------

uint3 threadIDToCell( uint3 DTid, uint3 Gid )

{

    uint3 output;

    output.x = DTid.x - 2 * Gid.x - 1;

    output.y = DTid.y - 2 * Gid.y - 1;

    output.z = DTid.z - 2 * Gid.z - 1;

    return output;

}

//--------------------------------------------------------------------------------------

// getBufferIndex

// given a thread DTid and group Gid, calculate the corresponding cell index in the buffer

//--------------------------------------------------------------------------------------

uint getBufferIndex( uint3 DTid, uint3 Gid )

{

    uint3 wrapped;

    wrapped.x = ( DTid.x - 2 * Gid.x - 1  + BUFFER_SIZE_X ) % BUFFER_SIZE_X;

    wrapped.y = ( DTid.y - 2 * Gid.y - 1  + BUFFER_SIZE_Y ) % BUFFER_SIZE_Y;

    wrapped.z = ( DTid.z - 2 * Gid.z - 1            + BUFFER_SIZE_Z ) % BUFFER_SIZE_Z;

    return wrapped.x + (wrapped.y * BUFFER_SIZE_X) + (wrapped.z * BUFFER_SIZE_X * BUFFER_SIZE_Y);

}

@cotrf: I would look into AMP.

http://channel9.msdn.com/search?term=amp