[Zlib-devel] Z_RLE for zlib-1.2.0

[Cosmin Truta]

Hello, zlib developers,

About a year ago I was promising to implement a new strategy, Z_RLE.

Well, I am happy to bring it to you now, just in time (I hope) for
the release of zlib-1.2.0.

See

  http://www.cs.toronto.edu/~cosmin/pngtech/z_rle/

or download

  http://www.cs.toronto.edu/~cosmin/pngtech/z_rle/deflate-120-rle-full.zip

There is not really much change in the source files, and most of it was
done some time ago, but I had to test it myself first, and decide there
are good reasons to stay that way. I had some bigger intentions, which
couldn't materialize due to lack of time.
The good news is that the essential work is done.

I felt it's important for this API addition to make it into the very
first of the zlib-1.2.x series, because it's easier to remember just
"the zlib-1.2.x series supports the Z_RLE strategy", rather than
"in order to compile your program that uses Z_RLE, you need at least
zlib-1.2.2" or so.

If, on the other hand, you cannot include the Z_RLE implementation in
the 1.2.0 release, I wrote an alternative as a dummy Z_RLE that acts
just like Z_HUFFMAN_ONLY. This should be easy to integrate, the changes
are small and straightforward.
Its advantage is that users' code won't break the compilation if it
is being built using zlib-1.2.0, instead of a later, required version.

The patch archives contain the modified versions of
zlib.h, deflate.c, gzio.c, minigzip.c, as well as "unified diff" files.

I run pretty intensive testing (I think), using OptiPNG. This way
I tested lots of combinations automatically.
minigzip and Info-Zip's zip are other programs I used for testing.

I also have other (minor) proposed changes for deflation. The web page
given above provides extensive information about the modifications, the
implementation decisions, and the testing involved.


Best regards,
Cosmin