Comment 2 for bug 1998470

Cross-referencing Ilya's comment about testing from here:
https://bugs.launchpad.net/ubuntu/+source/zlib/+bug/1982583/comments/7
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I ran tests 1-3 with Frank's 1:1.2.13.dfsg-1ubuntu3. They all pass; the performance improvement is also measurable.

Test 4 turned out to be meaningless: Ubuntu requires at least z13.
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Just notice that we have z13 as minimal required Z architecture starting with Ubuntu 20.04/focal anyway.