[GSoC] [WIP] ZSTD Compression with Dictionaries #4248
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This provides ROOT with a hook to train the compressor after the first FlushBaskets has been started, ideally providing higher compression ratios. The contents of the training is kept in the TBranch itself in a new nullable TBuffer member.
The R__unzip code was written in C and inside the compilation unit implementing the old decompression algorithm. This change puts R__unzip into the same compilation unit as the compression code that handles multiple algorithms.
Previously, the ZSTD output did not include the ROOT headers. This writes the headers out and allows the decompression engine to work accordingly.
…de, builtin zstd improvements are separated in other branch
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This PR is a WIP for implementing dictionary reusing within a branch in ZSTD. The work is based on previous work of Brian for the Compression Engine although it does not make use of any of the functions associated with training. This work depends on: #3947
Two extra file are added (ZSTDEngine2.hxx/cxx) that provide the infrastructure to perform a detailed analysis of the compression and decompression at basket level.
An analysis related with the current performance of this implementation can be found here.