Re: Decimal Floating types was RE: Information Systems Annex was RE: Dispatching and generics - language lawyer question

[dewar@gnat.com (Robert Dewar)]

"Robert C. Leif" <rleif@rleif.com> wrote in message news:<mailman.1029448504.10558.comp.lang.ada@ada.eu.org>...

> Since COBOL does not have a decimal floating point, COBOL 
> programmers, who still do most of the financial 
> applications, have not had a chance
> to try it!.

And why do you suppose COBOL does not have this? It is
because the COBOL standards committee does not consider
it worth adding. What does Robert Leif know that the
committee does not :-)

The point is that in financial calculations, you either
want absolute error control, e.g. in computing yields of
bonds, where very often the instruments specify the exact
algorithm in terms of fixed-point decimal.

Or you want approximate results rounded. There is no
requirement for mathematically accurate rounding for
decimal floating-point that I am aware of, so in practice
if you are doing approximate calculations, it is just fine
to do things in binary with sufficient precision and then
round the binary to decimal. Yes, there are marginal cases
where the double rounding can lead you to be "off" by 1 ulp
but there are no situations where this would matter.

Furthermore, as I noted before, there is no point in embedding such a
feature into the language. If you want
decimal floating-point, just use a library, there are many,
that supply this capability and make calls to this library.
That's what the compiler would do anyway.

COBOL programmers can perfectly well use such libraries.
COBOL is perfectly capable of calling library routines!

This seems a perfect example of a "requirement" generated
out of the blue, without full understanding of the actual
problem space.

The COBOL committee has been extremely adventurous in
extending the language (the COBOL object model is for
example more ambitious than that of C++ or Ada). If there
was the slightest good argument for adding decimal floating
point to the language, it would have been seriously considered.