Re: New Vax - future directions :-)

[Anders Magnusson <ragge%tethuvudet.se@localhost>]

> > > If you have two 64-bit values which you multiply, there is a fair 
> > > chance the result will not fit into 64 bits, and a carry won't be 
> > > enough to handle the overflow. :-) Then what? Just give up. Leave it 
> > > all to be done in software? Or add some instruction that can assist 
> > > you?
> > Yes, do it in software.  You don't have any modern language that want 
> > to deal with the upper part anyway.
>
> Ok. Fair enough. That wasn't a very meaningful example or question. 
> (Well, it's meaningful sometimes to assembler programmers, but hardly 
> for any higher level language.)
> But for the VAX32, having support allowing for efficient 
> multiplication of 64-bit values is something I see value in.
> I sortof see the same for a VAX64 to efficiently deal with 128 bit 
> multiplications as well.
> But as this does not extend to larger values, maybe it's questionable 
> how much value it do have in the end.
A side note: There is a very interesting part of the instruction set 
that I think should be investigated more - the packed decimal instructions.
Those will in fact implement arbitrary precision in hardware, which 
could be really nice to have when doing things like crypto calculations 
etc...

-- R