Mini-challenge - fastest 24 bit countdown

[IamRob]

I guess the routine I posted fails in one respect. If the Accumulator is already at $FF, then gets incremented to $00, then the subtraction at the bottom of the routine will fail as the carry will be cleared in that case.

[BigEd]

oh no!

[IamRob]

* I just had to revisit this thread as I couldn’t get this out of my head,

* This should be up there for one of the smallest/fastest
* The smallest

INY
INX
INC $0

LOOP EQU * ; 5 cycles per loop
DEY
BNE LOOP

DEX
BNE LOOP

DEC $0
BNE LOOP

RETURN RTS


* The fastest

INY
INX
INC $0 ; or INC for 65c02

LP EQU *
DEY
BNE LP
BEQ DOX

LOOP EQU *
DEY
DEY
DEY
DEY
DEY
DEY
DEY
DEY
DEY
DEY

DOX EQU *
DEX
BNE LOOP

DEC $0 ; or just DEC for 65c02
BNE LOOP

RETURN RTS