Re: Information Systems Annex (usefulness of Decimal Floats)

["Warren W. Gay VE3WWG" <ve3wwg@cogeco.ca>]

Robert Dewar wrote:
> "Robert C. Leif" <rleif@rleif.com> wrote in message news:<mailman.1029282844.28090.comp.lang.ada@ada.eu.org>...
> 
>>Ada decimal types (as currently defined) are fixed-point
>>types.
>>
>>Are you asking for decimal floating-point?
> 
> Decimal floating-point would be quite useless in financial
> applications as far as I can see (COBOL does not have this
> facility). 

"Useless" is extreme. There are situations where decimal floating
point is useful in computing financial values, but normally as
intermediate results. The final values of financial calculations
are obviously stored in fixed point.

Currency conversions are often performed in floating point
decimal since the currencies move all over the map in
relative terms in terms of scale. As long as the precision
is maintained in the intermediate results, and that you
properly anticipate the resulting scale and precision, the
use of decimal floats as intermediates work well, with
the final results being stored in a fixed point decimal form.

One recent example of this, was the Euro conversion,
where we had to do those triangulation computations (three
currencies were involved). You have a broad range of values
between British pound and the Turkish Lira, for example.

For smaller numbers you might still cry foul, but when you're
computing the asset value of fund or fund(s) or management
company(ies), you run into larger numbers ;-)

Again of course, you _could_ structure your computations such
that you don't need decimal floats, but this requires
extreme care and good testing (something you don't often
get from junior programmers - but that is a different issue ;-).
So often it is just easier and safer to use decimal floats
provided that the necessary precision is maintained.

As a side note I should mention that in C/C++ code, floating
point decimal is really the only other choice to binary
floating point values. Database vendors INFORMIX
and ORACLE for example, provide routines for decimal
floating point computations (but not for fixed point).
--
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg