It's beeen a long time, but I seem to remember that the command LDIR was
really easy to use and very fast!??
love
Freya
----- Original Message -----
From: Laurens Holst <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, November 15, 2001 2:01 AM
Subject: Re: Large loops (was: Z80 loops)
> > In general, for a loop with more than 256 steps, I use the following
> > code:
> >
> > ld bc,ITERATIONS
> > LOOP: push bc
> > ...
> > (whatever must be done ITERATIONS times)
> > ...
> > pop bc
> > dec bc
> > ld a,b
> > or c
> > jr nz,LOOP
>
> Faster is:
>
> ld b,ITERATIONS mod 256
> ld c,(ITERATIONS-1) / 256 +1
> LOOP:
> {do whatever you want to do, just don't mess with BC}
> djnz LOOP
> dec c
> jp nz,LOOP
>
> You use the 8-bit djnz for a 16-bit loop (much faster than dec bc : ld a,b
: or
> c : jp nz,LOOP, difference is 11 T-states). The additional '16-bit code'
(still
> faster than the dec bc : ld a,b : or c : jp nz,LOOP sequence, to be
precise 2 T
> states :)) is only executed once every 256 loops. Plus, it doesn't modify
the A
> register, which can be quite useful.
>
> If you want to use a variable loop count (number of loops provided in DE),
you
> can use the following code instead of the initial ld b,bla and ld c,bla
> instructions:
>
> dec de
> inc d
> inc e
> ld b,e
> ld c,d
>
> Very fast code (only 22 t-states), and only executed once.
>
>
> Greetings,
>
> ~Grauw
>
>
>
> --
> For info, see http://www.stack.nl/~wynke/MSX/listinfo.html
>
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