a second adder configured to modulo add {HEAD ~ an output} of {TAIL ~ the fixed MD5 nonlinear function processing unit} and the first adder 
of
a second adder configured to modulo add { HEAD ~ an output } of { TAIL ~ the fixed MD5 nonlinear function processing unit } and the first adder
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH