Re: Apple and the Holy War

[dempson@actrix.gen.nz (David Empson)]

Paul Schlyter <pausch@saafNOSPAM.se> wrote:

> In article <20000506192421.16108.00001856@ng-fh1.aol.com>,
> Regnirps <regnirps@aol.com> wrote:
>  
> > pausch@saafNOSPAM.se  (Paul Schlyter) wrote:
> >  
> >> 3. Use table-lookup whenever feasible.  Computations of e.g.
> >> trigonometric function at low precision can be greatly speeded up
> >> by using table lookup and perhaps linear interpolation between
> >> two table values.
> > 
> > I did a pile of 6502 enhancement tricks back when the Apple IIe first
> > came out.  I made ROMs to do things like "instant multiply" of two
> > bytes where the two bytes form the address of the result in two ROMs,
> > a MSB and LSB. So a multiply was basically write write read read
> > (or STA STX LDA LDX) in zero page since I mapped the 4 addresses
> > in ZP. What is that? 8 cycles?
  
[snip]

> In that particular case it would have been advantageous to use the
> 6802 instead, since that CPU did have an 8-bit multiply instruction.
> It had two accumulators, A and B, and the instruction MUL did multiply
> A by B, storing the 16-bit result in A+B.

No it didn't.  The 6800, 6802 and 6808 have A and B accumulators, but
don't support the combined 16-bit D accumulator, and hence don't have
the MUL instruction.  (I just confirmed this in the 6802 data sheet.)

You are probably thinking of the 6801 or 6803, which do have this
feature.  (Or the 68HC11, which is derived from the 6801.)

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand