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Re: sizemax() and 64-bit systems


From: Mike Miller
Subject: Re: sizemax() and 64-bit systems
Date: Mon, 13 Aug 2012 12:50:26 -0500 (CDT)
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)

On Mon, 13 Aug 2012, Martin Helm wrote:

Just a very short comment from my side, since I do not use the
enable-64bit switch when compiling octave. The problem is obviously not
so much if the libraries are compiled for 64bit (all my libraries are),
but that the default size for an integer in the fortran libraries is set
to 8 byte instead of 4 byte, at least that was my understanding last
time I looked at it.
I can be completely wrong here.


I was getting some info from here...

http://www.gnu.org/software/octave/doc/interpreter/Compiling-Octave-with-64_002dbit-Indexing.html

...which included this:

"all numerical libraries used by Octave will also need to use 64-bit integers for array dimensions and indexing. In most cases, this means they will need to be compiled from source since most (all?) distributions which package these libraries compile them with the default Fortran integer size, which is normally 32-bits wide."

So the problem is with the indexing, not with the memory addressing.

I guess FORTRAN uses signed integers for indexing which really means we have 31 bytes for positive indexing, not 32. I don't understand the negative index, but I'm not much of a computer scientist!

Mike


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