* RLA, RRA, RLCA, RRCA are essentially optimized versions, one byte smaller and one M-cycle faster, of RL A, RR A, RLC A, RRC A.
* ADD HL,HL is 3 bytes smaller and one M-cycle faster than SLA L; RL H.
* Unconditional JR is one byte shorter than unconditional JP and takes the same amount of time on CPC.
* To set A to zero, XOR A is one byte smaller and one M-cycle faster than LD A,0.
* To check if A is zero, AND A or OR A are one byte smaller and one M-cycle faster than CP 0.