Re: 6/8 bits imm instructions ( was Re: Rep:Re: [f-cpu] statistics of direct indexing usage)

[Michael Riepe <michael@stud.uni-hannover.de>]

On Fri, Jan 10, 2003 at 09:38:38AM +0100, devik wrote:
> > > > like to use this particular combinaison?).
> > >
> > > uh uh, can you give me please some examples of such instruction ?
> >
> > It's the problème of bit 12-13 (manual 0.2.5).
> >
> > It's use in the scan instruction to bit-reverse the input or negate it.
> > It used as negate sign flag of the MAC instruction. All of this flag
> > can't be used in the 8 bits immediat of such fonction. So is a pain or
> > not ?
> 
> scan and mac doesn't use 12-13 (mac uses it for reg3) according
> manual 2.7. And why do you want to use immediates for scan !?

I guess he's counting from the other side (that is, opcode in 0-7).
In that case, 12-13 would be the two flags that will be lost if you
extend r3 (17-12, in the official counting scheme) to an imm8 (19-12).

In case of scan ([lm]sb[01]), a third operand doesn't make sense, be
it register or immediate. `maci', on the other hand, might be an
option - but that one has room for an 8-bit immediate.

-- 
 Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
 "All I wanna do is have a little fun before I die"
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