Difference between revisions of "Z80 Routines:Optimized:addAtoHL"

Revision as of 01:41, 9 November 2009

This is an optimized addAtoHL. It is a little faster and doesn't need another 16-bit register.

Also it can be changed to add A to any 16-bit register. The only down side is one extra byte.

Use it as a subroutine (don't forget the ret) or macro.

Normal way:

	ld d,$00
	ld e,a
	add hl,de
;4 bytes and 22 clock cycles
 

Alternatives:

addAtoHL:
	add a,l
	ld l,a
	adc a,h    ;^ these two lines
	sub l      ;v increase h if there is carry
	ld h,a
;5 bytes and 20 clock cycles
;but no other 16-bit register messed up
 

Thanks to CoBB.

Another alternate way which uses branching and saves 1 T-state on one path (when carrying to h) :

addAtoHL:
	add a,l
	ld l,a
	jr nc, $+3
	inc h
;5 bytes, 19/20 clock cycles