Zipped octave file formats and octave core and default file formats

[David Bateman]

Dear All,

At the request of John, I am moving a discussion we were having to the 
maintainers list... I recently implemented gzipped file formats that 
allows all octave file formats, including matlab file but excluding hdf5 
files, to be saved gzipped using zlib. The files can easily be unzipped 
with "gzip -d". This is controlled by the "-z" flag to the save command. 
At the same type I added support for the Matlab v7 miCOMPRESSED format, 
so the majority of matlab v7 files (ie. those not using miUTF16 or 
miUTF32 formats) can be loaded and even saved.

However, this implementation raises a question of how to treat the issue 
of defining the octave core and default file formats. At the moment 
these are defined by the variables octave_core_file_format and 
default_save_format. The Matlab v7 format can be defined here as this is 
a real new file format, but the other compressed formats are just the 
old file formats run through zlib and are use like "save -binary -z 
...". Whereas the variables octave_core_file_format and 
default_save_format are defined as a single string without the "-".

There are three basic ways we could add the capability to define a 
compressed file format for the core and default save formats, these being

1) Add a new variable for core and default formats to store the options 
to use

2) Add new file formats like "zipped-binary"

3) Change the meaning and probably the name of octave_core_file_format 
and default_save_format so that they are the options to use to save 
rather than a file format. That is "binary" becomes "-binary" and zipped 
files might be defined like "-binary -z" in the core and default file 
options variable (whatever they are called)

The first two options have the advantage of being backward compatible, 
but both involve rather crufty changes to load-save.cc to allow them to 
work. The third option is NOT backward compatible but allows a cleaner 
implementation, and so I propose the third solution as the best one to 
pursue. However, I'd like comments on this beforehand, especially from 
those that actually use these options...

Regards
David

--
David Bateman                                address@hidden
Motorola Labs - Paris                        +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
91193 Gif-Sur-Yvette FRANCE

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