Slight optimization to legacy operand decoder by using a lookup map rather than generating masks every time
Slight optimization to legacy operand decoder by using a lookup map rather than generating masks every time

spthaolt/jemul8,spthaolt/jemul8,asmblah/jemul8,spthaolt/jemul8,asmblah/jemul8,asmblah/jemul8