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G.3 Compiling Octave with 64-bit Indexing

Note: the following only applies to systems that have 64-bit pointers. Configuring Octave with --enable-64 cannot magically make a 32-bit system have a 64-bit address space.

On 64-bit systems, Octave is limited to (approximately) the following array sizes when using the default 32-bit indexing mode:

double:         16GB
single:          8GB
uint64, int64:  16GB
uint32, int32:   8GB
uint16, int16:   4GB
uint8, int8:     2GB

In each case, the limit is really (approximately) 2^{31} elements because of the default type of the value used for indexing arrays (signed 32-bit integer, corresponding to the size of a Fortran INTEGER value).

Trying to create larger arrays will produce the following error:

octave:1> a = zeros (1024*1024*1024*3, 1, 'int8');
error: memory exhausted or requested size too large
       for range of Octave's index type --
       trying to return to prompt

You will obtain this error even if your system has enough memory to create this array (4 GB in the above case).

To use arrays larger than 2 GB, Octave has to be configured with the option --enable-64. This option is experimental and you are encouraged to submit bug reports if you find a problem. With this option, Octave will use 64-bit integers internally for array dimensions and indexing. However, 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.

The following instructions were tested with the development version of Octave and GCC 4.3.4 on an x86_64 Debian system.

The versions listed below are the versions used for testing. If newer versions of these packages are available, you should try to use them, although there may be some differences.

All libraries and header files will be installed in subdirectories of $prefix64 (you must choose the location of this directory).

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