Well our new friend is not very clear what are your doubts .. It seems that you don't believe in some magic .Listen Sytem generator is a generator of a fixed number DSP functions .. what Simulink does is just passes the parameters to produce those blocks for the functions that you simulated with the SUMULINK enviroment .. The VHDL code generated is reliable ,because it was designed to produce straight forward synthetized code .System generator won't generate a weird function not implied in the simulink toolbox ! So if you give the wrong parameters you are at fault !. There are other tools to synthesize MATLAB language .. but there are so many intrinsic function in matlab . that this MATLAB synthesis compiler being so new hasn't mapped yet .. On top is too expensive ($35,000) that is not worth mentioning ..