Those six instructions amount to: # a += (*p++) * (*q++) mov x qi , mov y pi , mov b p*q , add , mov a a+b , [fiddle with index registers or store result]

Those six instructions amount to: # a += (*p++) * (*q++) mov x qi , mov y pi , mov b p*q , add , mov a a+b , [fiddle with index registers or store result] It only looks tricky because the operation is manually scheduled onto a fairly deep pipeline, so each unit is doing its phase of a different iteration of the loop in any given cycle.