On Fri, 11 Feb 2000, James Newton wrote:

> Doh! adding A2 twice does not multiply by 2! Thanks for spotting that one.
>
> >-92 = 0xa4
> > and 0xa4 << 1 is 0x48
> yes, but 0x48 or (72 + x) mod 256 is (x-184) mod 256 or in other words,
> adding 72 and wrapping around 256 is the same as subtracting 184. I think
> I'm right on that one.

True but, there's also that carry bit. A two's complement can be written
in terms of a one's complement:

two's complement of x = 1 + one's complement of x.
So, taking this snippet from your web page:

> >>>     rlf     Tens,f  ;B1 = 2*(4A2+A1-92) = 8A2+2A1-184
> >>>     rlf     Ones,f  ;B0 = 2*(A3+A2+A1+4) = 2A3+2A2+2A1+8
>         comf    Ones,f  ;B0 = -2A3-2A2-2A1-8
>         rlf     Ones,f  ;B0 = 2*(-2A3-2A2-2A1-8) = -4A3-4A2-4A1-16


     rlf     Tens,f  ;B1 = 2*(4A2+A1-92) = 8A2+2A1-184 (I'll leave this)
     rlf     Ones,f  ;B0 = 2*(A3+A2+A1+4) = 2A3+2A2+2A1+9
     comf    Ones,f  ;B0 = ~(2A3+2A2+2A1+9) = -2A3-2A2-2A1-8
     rlf     Ones,f  ;B0 = 2*(-2A3-2A2-2A1-8) = -4A3-4A2-4A1-16

The comf's comment is still the same...

So now that I think about it, Payson new what he was doing (ah, should I
have ever doubted...)

Scott