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