Yes, the program uses the Pouchou and Pichoir – Simplified XPP method as described in many documents released about the program.
I've searched on various websites and I encountered the same information on all of them. They all indicate the usage of the method you have mentioned above.
You can also download a document with slides that provides some information about this: http://www.geology.wisc.edu/~johnf/g777/ppt/60_ZAF.ppt
Note: You need a compatible PPT viewer to open that file (Microsoft Office, LibreOffice, OpenOffice etc. )