Re: A82: fast multiply...

To: assembly-82@lists.ticalc.org
Subject: Re: A82: fast multiply...
From: Henrik Edlund <piett@piett.com>
Date: Sun, 3 Aug 1997 12:02:15 +0200 (MET DST)
In-Reply-To: <32031F35.82DF6AE5@swipnet.se>
Reply-To: assembly-82@lists.ticalc.org

 This is directly from "Programming the Z80" by Rodney Zaks. It's very 
optimized, but it could be unrolled to further speed it up. 
   ;HL=L*E 
    ld B, 8 
   MULT: 
    add HL, HL 
    jr nc, NOADD 
    add HL, DE 
   NOADD: 
    djnz MULT 

On Sat, 3 Aug 1996, Lars Ahlzén wrote:

> Hello!
> As the Z80 doesn't have a multiply instruction (which is almost
> necessary for star-scrolls and things like that) then I've tried to do
> my own routines. It surely works, but I think it takes more than 80
> cycles to execute. (here's the code:)
> 
> Multiply:
> ; Multiplies b and de and gives the product in hl
>     ld  hl,0
>     ld  a,1
> mulloop:
>     ld  c,a
>     and b
>     jr  z,noadd
>     add hl,de
> noadd:
>     ld  a,c
>     sla e
>     rl  d
>     add a,a
>     jr  nc,mulloop
>     ret
> 
> Someone must have written a faster way of mulitplying two 8-bit numbers
> than this, or...? If so, could you reply to this and show your routines?
> 
> (by the way: is there a fast way for integer division, too?)
> 
> Lars Ahlzen
> lars.ahlzen@swipnet.se
> 

--------------------------------------------------
Henrik Edlund                    Piett Productions
piett@piett.com              http://www.piett.com/

  "They were in the wrong place at the wrong time.
Naturally they became heroes."
                  Leia Organa of Alderaan, Senator
--------------------------------------------------

References:

A82: fast multiply...

From: "Lars Ahlzén" <lars.ahlzen@swipnet.se>