Re: [Axiom-developer] Left shifts of negative numbers

[Dylan Thurston]

On Tue, Oct 14, 2003 at 07:06:07PM -0400, Page, Bill wrote:
> [ Some of your emails arrive as text file attachments to
> otherwise empty emails (such as this one) and other times
> as ordinary email? Are you sending an unusual format to
> the axioim mailing list? (e.g. HTML or "rich text" format). ]

It's because I habitually sign my e-mails, and that's how the mailing
list software deals with it.  I'll stop if it's too annoying.

> ... Oddly, I could not find any definition for
> QSLEFTSHIFT.

It's defined as a macro equivalent to ash for fixnum's in
src/interp/vmlisp.lisp.pamphlet.

> Failing finding a native Lisp function that does the
> job, how about defining it as
> 
>   shift(x,y) == integer(ASH(x-1,y)$Lisp)+1

In the case when x and y are both negative, I think this gives the
"round towards zero" semantics that seem to be expected.  An
alternative is

  shift(x,y) == -integer(ASH(-x,y)$LISP)

which might be clearer.

Peace,
        Dylan