Hi!
A snippet for the beginners like me

To add an 8 bit value (a) to a 16 bit register (hl) I used to do this:
That takes 22 cycles and destroys an additinoal register (de).

There is a way to do the addition without using any additional register, slightly faster (20 cycles) but 1 byte longer:
Note that bc register or de register can be used instead of hl.

Oh, not mine; just found on the internet. Can't remember where; maybe here.
Strangely, it is not in the classical "Z80 maths" pages That's why I put it here.

You're right. I'm a newbie; I forgot about the M1 cycle
Anyway, it's still useful if other registers cannot be detroyed (the push/pop pair would make the code longer and slower) or if the operation to accomplish is bc+=a or de+=a.