Usage of JCXZ/JCXNZAssembler/8086

I've seen many programs which use the inefficient code:

        or      cx,cx
        jz      label
when they should use
        jcxz    label
However, not so obvious is when the code is:
        or      cx,cx
        jnz     label
You can still reduce this by one byte with a 3-byte alias for
        jcxnz   label
by using:
        inc     cx
        loop    label
If CX began as zero, the INC sets it to 0001. That is also the only situation where the LOOP command would permit the code to fall through to the next command instead of looping to the label.
This alias for JCXNZ does affect some flags, so might not be usable in all situations.
Gem writer: Mark Andreas
last updated: 1998-03-16