[PLUG] Compressed data files

[Bill Barry]

Ah yes, the lossy compression algorithm implemented many years ago
rm filename

Bill

On Mon, Nov 11, 2002 at 09:36:31PM -0800, Matt Alexander wrote:
> If you really want to reduce the file sizes for your programs, check out
> lzip:
> http://lzip.sourceforge.net/
> It provides better compression than even bzip2, which is pretty
> impressive.
> ~M
> 
> 
> On Mon, 11 Nov 2002, Bear Giles wrote:
> 
> > Ed Sawicki wrote:
> > > I'm wondering how some programs deal with data files that
> > > are sometimes compressed using gzip. I haven't yet written
> > > code for this.
> >
> > The zlib (and bz2lib) libraries are easy to use.  You can either use the
> > stdio-ish routines, e.g., zfopen(), zread(), zprintf(), or call the
> > inflater and deflater routines directly.  That takes a bit more work,
> > but it gives you *much* more flexibility in doing things like inserting
> > a Z_SYNC_FLUSH after every meaningful chunk of data (e.g., every file in
> > an archive) so that you can recover the maximum amount of data even if
> > the file is subsequently corrupted.
> >
> > As for gzip in particular, it's a well-documented format that provides a
> > wrapper around the zlib output.  Things like original filename,
> > timestamp, and at the end of the file the uncompressed size and CRC
> > checksum.
> >
> > Put it all together and you get a very nice function that I'm surprised
> > has never been put into a library - maybe it's just too obvious - ...
> >
> > 1) open the file
> > 2) lock it
> > 3) mmap it
> > 4) check the first few bytes - if it's a GZIP file mmap a buffer large
> > enough to hold the uncompressed data and blitz your original file into
> > the second mmap file.  Unlock and close the original file.
> > 5) return the structure containing the information needed when you close
> > the file - file pointer, locks, mmap ptr, etc.
> >
> > This is the type of code that can be a pain to get right the first time,
> > but once you have it working it can be reused everywhere and you wonder
> > how you ever got by without it.
> >
> >
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> > http://lists.pdxlinux.org/mailman/listinfo/plug
> >
> 
> 
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