A backdoor in xz

Indeed; I somehow totally missed that when glancing over zstd's options earlier today. Thanks for pointing that out.

Interestingly it does worse than "xz -T0" does wrt. how many cores it can effectively use. On my 32-core system with the same 1.6 GB input file "zstd --ultra -22 -T0" starts out using four cores but drops down to & stays at three cores after a handful of seconds. Therefore processing still takes 7m38s. Using a file or STDIN as input makes no difference. I guess zstd simply cannot segment the source as much as xz does.

Now "xz -T0" (which is the default in recent xz versions) also only uses eight cores on the same machine. Then again even with "-9" it is worlds faster both per core & in total than "zstd --ultra -22".

Then again, I'm really not trying to argue that xz is better than zstd, even though I probably sound like it. I just tried to answer the question why the OSS community has adopted xz as widely as it has, simply to satisfy my own curiosity. Also it's good to know the strengths & weaknesses of the various tools at our disposal.