trying to understand the suignal line component of the standard MACD.mql4 code

 

Hello forum, I was looking at the standard MACD.mql4 code using  the MetaEditor, as I try to learn to code by example.

It all seemed straight forward  for the calculation of the ExtMacdBuffer, but I am confused as to how "double    ExtSignalBuffer[];" is calculated or is populated by SimpleMAOnBuffer

Is SimpleMAOnBuffer (line 85) a function similar to iMA and if yes, could someone point me to an explanation similar to that provided for iMA  at https://docs.mql4.com/indicators/ima

I need thes things defined with crystal clarity at this point of my learning and the references to "rates_total", "prev_calculated" etc within the calculation occurring at line 85 have me a little confused 

85     SimpleMAOnBuffer(rates_total,prev_calculated,0,InpSignalSMA,ExtMacdBuffer,ExtSignalBuffer);


thanks in advance

iMA - Technical Indicators - MQL4 Reference
iMA - Technical Indicators - MQL4 Reference
  • docs.mql4.com
iMA - Technical Indicators - MQL4 Reference
Files:
MACD.mq4  4 kb