Re: [f-cpu] Reamrks and suggestions about the manual

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

On Mon, Jul 08, 2002 at 12:06:57AM +0200, Yann Guidon wrote:
[...]
> > > At the top of the page you say 'logici.xxxx' so I understand this style
> > > of codding 'logici.0111' like for the logic operand but ater you say
> > > 'logici.s' like for bitop, we must clarify this and I think it was best
> > > to have the same form for logic and logici even if we don't have all the
> > > function of logic in logici.
> > 
> > The `logic[i].xxxx' instruction is obsolete. And it's rather hard to
> > grok right because the function encoding is non-intuitive - e.g. does
> > `logic.0010 A, B, C' mean `A and not B' or `B and not A'? Is `logic.0001'
> > an AND or NOR operation? Both variants are possible, depending on the
> > interpretation of the function field.
> 
> There is another problem : when one of the operands is negated
> (ANDN and ORN), which one is it ?

Since all operands have the form

	operation r3-or-imm8, r2, r1

and the mathematical interpretation is

	r1 := r2 <op> r3

and `andn' means `and not',

	r1 := r2 and not r3

is the logical choice.

-- 
 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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