Matthew Knepley wrote: > On Wed, Nov 4, 2009 at 2:06 PM, Barry Smith <bsmith at mcs.anl.gov > <mailto:bsmith at mcs.anl.gov>> wrote: > > > This is tricky because some C/C++ compilers long double uses 128 > bits of space but actually (on Intel) only uses 80 of the bits > (those are the bits that floating point unit handles). So you do not > really get 128 bits. Also MPI may not properly handle the 128 bit > doubles. > > > I figured that his types were just C++ types once he said they were > provided by a package.
QD is honest quad-double (32 bytes, all of them significant) http://crd.lbl.gov/~dhbailey/mpdist/ They are C++ types with appropriate overloading, but the operations are implemented in terms of conventional double-precision where as "long double" is a different beast. > I am investigating qd now. Is there any MPI implementation that > uses qd? Do you need MPI? > > > Can't we just make a type the correct number of bytes long? I think so (on homogeneous hardware), but you have to create your own version of each MPI_Op that does the right thing with this longer type. Jed -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 261 bytes Desc: OpenPGP digital signature URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20091104/ffa96917/attachment.pgp>