The fixed nonlinear function processing units in {TAIL ~ a given stage} implement {HEAD ~ only the nonlinear function} needed for the MD5 round being performed by the stage 
The fixed nonlinear function processing units in { TAIL ~ a given stage } implement { HEAD ~ only the nonlinear function } needed for the MD5 round being performed by the stage
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH