Re: 3DLDF

[Frank Heckenbach]

Hans Aberg wrote:

> At 01:52 +0100 2004/08/16, Frank Heckenbach wrote:
> >> The arithmetic operations, I think, though, will preserve precision
> >> length. But someone wrote on top of GMP a C++ library that sort backwards
> >> tries to figure out a dynamic precision.
> >
> >Seems useful in many cases, problematic in others (does it add the
> >factor's precisions in a multiplication?), impossible in some (sqrt,
> >even most divisions).
> 
> I do not myself believe in this idea.

Well, you brought it up here.

> In the beginning of the eighties, people using the popular Borland Pascal
> compiler (which you are cloning?)

No thanks (only some backward-compatible features of it for legacy
code). It doesn't really implement the original Pascal language to
start with, leave alone newer versions, and does a lot of unportable
things.

> remarked its multiprecision very useful.

Borland Pascal itself didn't have any multiprecision. There may have
been external libraries for it (perhaps similar to GMP), I don't
know.

> There are still new standard revisions of C, latest is C99. Is Pascal still
> being developed?

Sure. Though the latest ISO/ANSI standard is from 1990, there have
been standard drafts etc. since them. I don't know when the
committee will get together to formalize them, but I don't care so
much ...

> >Most texts about numerical algorithms that I know do their
> >computations with real numbers indeed and talk about rounding
> >errors. (Of course, computing the rounding errors requires knowledge
> >about the (floating-point or other) implementation. But it requires
> >more detailed information than just that it's floating-point, which
> >is all that C guarantees.)
> 
> This is why it is important to distiguish the flotang point type from other
> numerical types, such as the real numbers.

My point was that only knowing *that* it's floating point, without
knowing all the parameters, doesn't help too much.

Frank

-- 
Frank Heckenbach, address@hidden
http://fjf.gnu.de/
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