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<DIV dir=ltr align=left><SPAN class=932433315-04092008><FONT face=Arial
color=#0000ff size=2>Terabytes are pushed back and forth already now, maybe not
yet in one piece. MPI-3 is a couple of years away, by which time who knows what
may happen. Anyway, you're right, this may not be an immediate
concern.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=932433315-04092008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=932433315-04092008><FONT face=Arial
color=#0000ff size=2>At the moment, IBM Power apparently implements lp64 model.
We typically see the same thing on Intel 64 based platforms. Our compiler's
long long is 64 bit in that case, too. Same on Itanium. The latter already
has several multiply/add commands with an intermediate full 128-bit
product out of 64-bit int operands, and the corresponding compiler intrinsics,
however.</FONT></SPAN><BR></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
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<FONT face=Tahoma size=2><B>From:</B> mpi-22-bounces@lists.mpi-forum.org
[mailto:mpi-22-bounces@lists.mpi-forum.org] <B>On Behalf Of </B>Richard
Treumann<BR><B>Sent:</B> Thursday, September 04, 2008 5:25 PM<BR><B>To:</B> MPI
2.2<BR><B>Subject:</B> Re: [Mpi-22] New proposal: Support for large message
counts<BR></FONT><BR></DIV>
<DIV></DIV>
<P>Are there systems today that use a 128 bit long long? Are there virtual
memory systems or filesystems coming in the reasonable future that use a 128 bit
address range?<BR><BR>On IBM Power we support both 32 bit and 64 bit
executables. For both 32 bit and 64 bit executables, the C compilers treat int
as 32 bits and long long as 64 bit. C long differs so is 32 bits in a 32 bit
executable and 64 bits in a 64 bit executable (I.E. big enough to hold an
address/pointer). <BR><BR>The jump from 32 bits to 64 bits is a factor of 4
billion so it may be goodness in the abstract to think about what comes after 64
bits gives way to 128 bits, should we consider this a real problem?<BR><BR>I do
not see much reason to worry about the fact that multiplying 2 arbitrary 64 bit
values can overflow a 64 bit result unless we think some real situation will
call for 128 bit results. <BR><BR><BR><BR>Dick Treumann - MPI Team <BR>IBM
Systems & Technology Group<BR>Dept X2ZA / MS P963 -- 2455 South Road --
Poughkeepsie, NY 12601<BR>Tele (845) 433-7846 Fax (845)
433-8363<BR><BR><TT>Alexander</TT> wrote<BR><TT><snip></TT><BR><TT>>
Another thing is that if we multiply to long values, the result may <BR>>
potentially overflow a long. So, for a library that allows long <BR>> counts
and long datatype extents, the internals of the library will <BR>> have to be
long long. long long (128 bit) arithmetic may be rather <BR>> expensive on
some CPUs. So, the 64-bit interface should probably be
optional.</TT><BR><TT><snip><BR></TT></P><pre>---------------------------------------------------------------------
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