Date:         Thu, 7 Jul 2005 01:37:14 -0400
Reply-To:     Richard Ristow <wrristow@MINDSPRING.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Richard Ristow <wrristow@MINDSPRING.COM>
Subject:      Re: precision & size limits
In-Reply-To:  <200507070510.j675AZnj006221@listserv.cc.uga.edu>
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At 01:10 AM 7/7/2005, Jack Hamilton wrote:

>I've asked for an infinite (or 1 x 10**32000, which is pretty close to
>infiite for most purposes) data type in SAS, similar what already
>exists in REXX, but have always been told that it would be too
>slow.  Too slow compared to what, I wonder - calculating numbers by
>hand?

I'd have called computation speed a non-starter. If arithmetic is, say,
three orders of magnitude slower (probably a great over-estimate,
though I'd expect at least one order of magnitude), well, the existing
data representation is still there and still fast. If you do need huge
dynamic range or huge precision, arithmetic three orders of magnitude
slower is surely faster than "calculating numbers by hand".

I would guess the proposal founders on three issues:
A. It's very rare to need it.
B. Statistical procedures almost always do arithmetic combining several
variables. You'd need not just arithmetic for the new representation,
but arithmetic to coerce standard form to expanded and then calculate.
C. This sounds like a deal-breaker: Most statistical procedures have
internal data structures, for things like SSCP matrices. Those are
almost certainly built around the assumption that all numbers are 8
bytes, and all of the same, standard, datatype. (The latter means that
the structure doesn't need any indication of datatype.) Probably most
statistical procedures would have to be heavily rewritten around a new
structure that accepts multiple datatypes.

There's also changing the representation of the PDV, but I expect that
would be much simpler.