Feature: Add XZ compression

[dnltz]

Hey @klayoutmatthias ,

I'm a huge fan of the integrated gzip support in KLayout! I always compress GDS files because they have a big compression potential. However, I have seen XZ compression is now used more and more in other open-source projects. I was wondering if you would be interested in added XZ as well as compression?

I can work on that feature, but I want to check whether you're interested or you see any blocker implementing this feature.

I just tried XZ on a random GDS file, I found on my disk, and the result is quite promising:

$ ls -lh 6_final.gds*
-rw-r--r-- 1 daniel daniel 106M Aug 21 11:18 6_final.gds
-rw-r--r-- 1 daniel daniel  17M Aug 21 11:18 6_final.gds.gz
-rw-r--r-- 1 daniel daniel 8.0M Aug 21 11:18 6_final.gds.xz

[klayoutmatthias]

Hi @dnltz,

If you want to have a more promising compression, use OASIS:

-rw-r--r-- 1 matthias matthias 31054670 Aug 17 14:54 sealring.gds
-rw-rw-r-- 1 matthias matthias     1436 Aug 19 23:47 sealring.oas

(testcase is here: #2423).

Frankly, I have no plans to add more compression formats. First, there is OASIS, second people will ask then for zip, bzip2 and whatever, third every library to include potentially creates a maintenance issue and forth, the zlib conveniently wraps compression/decompression in a transparent way, i.e. does not need a special decision whether the file is compressed or not - but there can only be one.

I should also add, that xz is slow: In the above example

• gzip: 5872478 Bytes, 2.9s
• xz: 2274680 Bytes, 16.6s
• OASIS: 1436 Bytes, 0.6s (KLayout strm2oas tool)

Matthias