[NeXus-tech] NeXus API and large arrays

[freddie.akeroyd at stfc.ac.uk]

Hi,

We have managed to create a rather large (>2 billion elements) one dimensional array on one of our instruments - this has caused issues with the NeXus API as the functions dealing with array dimensions are all signed 32bit integers. I have worked around this in the local implementation, but was wondering if some additions to the NeXus API would be the best solution for the future (in this particular case I intend to try and split data before it gets to this point in future, but I'm sure a similar situation could arise again elsewhere)

HDF5 uses hsize_t internally for array dimension, which is an unsigned 64bit type - my suggestion is that we create a set of new NeXus API functions handling "int64_t" dimensions (I suggest this rather than uint64_t as NX_UNLIMITED is -1 and I'm always a little cautious about casting negative numbers to unsigned). As for naming these functions, how about adding "64" to the end of the function name?

The main functions that would need adding are:

NXputslab64
NXgetslab64
NXgetinfo64
NXgetrawinfo64

The following should probably be added too for completeness:
NXmakedata64
NXcompmakedata64
NXmalloc64

Regards,

Freddie

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