wow I am amazed. Anyways no Fallen_Ghost was not saying that jr (a) is a valid instruction he was simply trying to prove a point of why it was not self-explanatory. He was saying hey why wouldn't jr (a) work. That is all.

I'm wondering, does ex (sp),ix/ex (sp),iy work?

Well the ex commands, unfortunately, are exceptions to that rule (last i checked)

EX (SP),IY and the like *do* work, according to the "documentation". They're slow, so I wouldn't recommend using 'em unless you ran out of registers or something (which is very likely in high-intensity situations).

It's just that EX DE,HL lacks that same kind of modifier. And don't we wish EXX had that kind of modifier?

But for some other assembly code optimizations...
( meh. I'm running out of things to say... )

To make use of the wonderful array of flags, you should make all loops that count decrement toward zero. In this way, you remove the needed CP instruction prior to the condition test and you cause the loop to run faster. If you're using register B for this purpose, then you should already be familiar with the DJNZ instruction. If you need something counting upward, however, you can use an extra register to keep track of the count. If you are running short on registers, you can do some CPL/NEG magic with the counter if the count upwards happens to be starting from 255 counting downward, or if the counting number happens to require that kind of value.

As with any ASM optimization, you ought to write your code first and then see if you can improve the code's form in any way. Whether it be taking advantage of a conveniently placed flag, condensing the code so it uses less registers, removing instances of "slow" instructions in favor of "faster" instructions, limiting the scope of what your code is doing to *exactly* what it should do... and making sure that if you make any changes to subroutines with its input, ensure that the input values of the calling routine are well-suited to handle the changes.

Sometimes, you will want to change input values to certain subroutines because the calling routine will usually have its input in a certain format. For example, if you needed a routine that would extract size bytes out of a program var right after a _chkfindsym, you'd take DE as the address of the program. If you're doing this multiple times, you're saving yourself a few bytes of having to do "EX DE,HL" each time you called _chkfindsym.

Experiment with these optimizations, but before you do any kind of optimization, please, for the love of all that is good, make sure that the program works prior to potentially breaking it. You'll thank yourself later.

hmm yes very nice calc84maniac. Simple yet straight to the point.

ADD HL,DE only modifies the carry flags, which doesn't matter in this case. ADC HL,DE, however, modifies the same flags as SBC HL,DE.