Stavros,
thanks again for your helpful comments.
Volker
PS: I guess there isn't any documentation about simp.lisp ?
Am 17 Mar 2008 um 16:23 hat Stavros Macrakis geschrieben:
> On Mon, Mar 17, 2008 at 3:20 PM, van Nek <van.nek at arcor.de> wrote:
> > Am 17 Mar 2008 um 13:55 hat Stavros Macrakis geschrieben:
> > > I would recommend that you choose either lsh or rsh as
> fundamental,
> > > and simplify the other one to it, e.g. rsh(x,2) == lsh(x,-2).
> >
> > Stavros, my intention is the here, to make clear the shift
> direction just by the functions
> > name. The original Lisp function ash (artihmetric shift) doesn't
> do so. But you are right,
> > lsh(x,-1) is understandable as a shift to the right.
>
> The name ash in Lisp is a historical remnant. lsh with a negative
> shift treated the integer as a fixed-size word and shifted in
> zeroes
> from the left; while ash shifted in ones from the left for
> negative
> numbers. With arbitrary-sized integers, the distinction is
> meaningless. Having one function rather than two is always
> better.
> Consider the identity lsh(x,1)-rsh(x,-1)=0. If rsh simplifies to
> lsh,
> this is handled trivially by the unmodified + simplifier. If not,
> there needs to be a special case in the + simplifier or a special
> simplification function.
>
> > integer_length(-1) returns 0, because for negative integers it
> returns the position of the
> > leftmost zero (the leftmost 1 in case of positive ints).
> > So integer_length(-2^100) returns 100.
>
> So integer_length(-n-1) = integer_length(n) for n>=0? And
> integer_length(0)=0?
>
> > > > if at least one arg is a string, a Maxima list or constant
> but not an integer => merror
> > > Why not extend to non-integers? logior(1/2,1/3) => 5/6;
> > It was not my intention to handle these numbers. I just looked
> into the Mathematica doc and
> > they also only care about integers.
>
> > Stavros, do you see an interesting application of such to
> rationals extended bitwise
> > operations ?
>
> No applications in mind, it just seems like a natural extension,
> so
> why give an error? Why not just leave unsimplified until someone
> comes along and programs this case? Certainly some cases are easy:
> logop(m/2^i,n/2^i) == logop(m,n)/2^i and preserve all the useful
> identities. If you don't allow this, then simplifying logand(x,x)
> is
> only correct if x is an integer.
>
> > > There are many other useful simplifications,
> > Right, these are useful simplifications. Can you give me any
> hint, how to manage them.
>
> Take a look at, say, simpmin to see how to write simplifying
> routines.
>
> -s
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