Re: IEEE Decimal Float on Itanium

On Fri, 08 Dec 2006 19:36:54 -0800, Arne Vajhøj <arne@xxxxxxxxxx> wrote:

Tom Linden wrote:
On Fri, 08 Dec 2006 12:06:31 -0800, Stephen Hoffman <Hoff@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
John Reagan wrote:
Most definitely. Currency calculations. Many (and I do mean MANY) applications incorrectly use binary floating point to manipulate currency. They often find out too late that 1.23 + 4.56 may not equal 5.79 (at least exactly). COBOL on Alpha and I64 have lots of software to emulate that decimal abilities on the VAX. Having it back in hardware might allow COBOL applications to see a performance increase.

The question should better have been "do you have something in particular here requiring integer values larger than, say, quadwords?" And if so, are the numbers of quadword (or larger) operations required going to see a particular benefit from the addition of hardware and/or software?

There are certainly organizations that are dealing with vast sums of money, though most also have the budgets needed for customized hardware.
We had a bit of a discussion on this topic in comp.lang.pl1 and I think
it was somewhat evenly divided on the value of this. The group I fell
into was of the opinion that scaled fixed decimal (which on VAX and Alpha
gives us 31 digits) was adequated for the task. The other group that it
was good because it would obviate FIXED OVER FLOW EXCEPTIONS, FOFL in PL/I
ecxception handling parlance.
As it turns out, studying the IBM papers on this, they use an encoding
techniques which gives them two additional digits of accuracy to 33, but
when the computations are performed they convert to packed decimal, bcd
format. My own feeling is that if they add this as a new data type in
C, for example, it would make C viable to be used in financial applications.
My god, have we sunk that low:-)

decimal is actually a builtin type in the newest "big" language: C#.
I presume that is IEEE (proposed) float decimal?

IBM could use C# via Mono on Linux running on zSeries hardware
Well the code generator would have to be taught to emit all those new
instructions

But Cobol or Java seems more likely on zSeries (BigDecimal is
a class in Java, but nothing prevents the JVM from JIT'ing
it to something hardware supported).

Arne



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