Interface from a C DLL to .NET

__declspec(dllexport) void __stdcall ProcessChunk(
    void *p_prochdl,
    const BIG_INPUT_STRC *p_inparams,
    BIG_OUTPUT_STRC *p_outparams
);

byte[] buffer = ...;
fixed(byte *pBuffer = buffer)
{
   // do something with the pBuffer
}

someValue = buffer[(elementsPerDimensions * x) + y];