Hi,

We recently upgraded zstd to 1.3.3 after reading about the performance improvements for high compression levels, and we were happy to see that the performance increase was very significant (around 40% for level 19). However, we also noticed that the output of zstd 1.3.3 is not binary-identical to zstd 1.3.2, and unfortunately that limits its usefulness for our particular use case because we rely on our compressed data not changing as we upgrade the libzstd library, which we'd like to do in order to get access to bugfixes, new features and performance improvements. We were previously using zlib which I guess hasn't had a bitstream-impacting change in many years.

Is bit-identical output across versions a goal of the zstd project, or do you expect these changes to happen for the foreseeable future?