All use macd = MA(fast) - MA(slow) and signal = MA(macd)
mt4 uses EMA(f/s, appliedPrice) and SMA(macd) others may allow different types of MAs
mt4 displays two lines macd/signal. Some display a histogram of macd instead of a line and others display the two lines and a histogram of the difference.
If you want to verify the difference between mt4's macd and "truemacd" You have to POST THE CODE, or a link - There are no mind readers here.
MACD - Wikipedia, the free encyclopedia