Alvaro Fernandez wrote:
>This is more or less what I expected. One issue I ran into a lot was that a
>double precision real on a Sun workstation was equivalent to single
>precision on a Cray.
>
>The trick was that single precision reals were supported in hardware on the
>Cray, whereas double precision were software implemented (at least when I
>dealt with them). If you just copied and recompiled your Sun code on the
>Cray, "double precision" would be the equivalent of quad precision w.r.t.
>the Sun - usually overkill for most applications, and slow to boot because
>you were not taking advantage of the Cray's hardware-implemented precision.
>And you would wonder why your code was slow on the supercomputer... I am
>willing to be corrected on this score if this is no longer an issue on the
>Cray.
>
>
>
The new Cray X1 system (the main product at the moment) is different
from the older Cray machines in that there is support for 32-bit data in
hardware and the floating point hardware is IEEE format. If you don't
specify any command line options, the default data size is 32 bits,
matching Sun and other workstation/server vendors. This should simplify
code porting. There is an option to change the default to 64 bits, at
which point it matches up with the older Cray systems (at least the IEEE
ones). The 128 bit precision operations are still software emulated.
Cheers,
Bill
--
Bill Long [log in to unmask]
Fortran Technical Support & voice: 651-605-9024
Bioinformatics Software Development fax: 651-605-9142
Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120
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