Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!hplabs!hpda!hpisod1!hpcllla!hpclisp!hpclcdb!cdb
From: cdb@hpclcdb.HP.COM (Carl Burch)
Newsgroups: comp.lang.fortran
Subject: Re: Want Fast Double Precision?
Message-ID: <6690011@hpclcdb>
Date: 30 Jan 88 23:33:00 GMT
References: <32300003@ccvaxa>
Lines: 27

> msf@amelia.nas.nasa.gov (Michael S. Fischbein) writes :
> 
> The HP Precision Architecture hardware floating point is faster at
> double precision than single precision.
> 
> I believe that is because it is 64-bits wide and must add a truncation
> instruction for single precision.  Anyone who knows the internals out there?

I just ran the Linpack and Whetstone benchmarks on our HP9000 Series 840,
and the ratios of the times were 1.44 and 1.52, respectively - both double 
longer than single.  (NOTE : Usual disclaimer about not being official
benchmark results, etc - even just as a ratio.  Actually, these are just
ballpark ratios : running benchmarks is almost as hard as writing them - 
which is impossible.)

These ratios will vary considerably with the implementation of the architecture,
but I haven't heard of a hardware implementation that does faster double than
single.  Of course, it's always possible for some programs to run faster in
double than single (faster converging algorithms, overflow traps in single, 
etc.).

The difference you may be thinking of is that the above ratios are not as
great as some other machines'.  That may well change as HP releases new
implementations of the Precision Architecture family.

							Carl Burch
							HP Fortran Team