Floating Point and Financial Software

[mpd@netcom.com (Mike Duvos)]

There seem to be a few mini-flames on the list over whether
floating point data representations are appropriate for financial
software.

In a nutshell, the answer is "YES", and the use of floating point
arithmetic is common in such applications.

One argument heard against the use of floating point is that it
is inherently "imprecise." In reality, floating point
representations and the results of floating point operations are
perfectly well defined, and the points on the real number line
which are exactly representable by double-precision floating
point values are usually a superset of those representable by the
default integer on most machines.

Storing monetary values as double-precision floats having integer
values in cents is even common in COBOL programs, where the
"COMP-3" data type allows the use of fast floating point in lieu
of the default and slow manipulation of packed decimal and
decimal data.

It is even common in certain CPUs, like CDC Mainframes and
SPARCS, which are primarily floating point engines, to omit
integer divide and sometimes even multiply, and to provide a
subroutine which employs floating point calculations to emulate
these operations. This is completely transparent to the user of
the machine, and there is no problem in using floating point to
do integer operations.

In fact, when running financial applications on large engineering
mainframes, which generally lack a business instruction set,
floating point is not only commonly employed, it is the obvious
way to get the maximum performance out of the machine.

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     Mike Duvos         $    PGP 2.6 Public Key available     $
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