zstd: Add Best compression mode #304
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Add slow compression mode, but with the best compression ratio available Allows a nice size improvement over "better" mode, but at a significant CPU penalty. Typical speed is currently around 20MB/s Some speed examples: ``` github-june-2days-2019.json zskp 1 6273951764 699045015 11634 514.29 github-june-2days-2019.json zskp 2 6273951764 617881763 17756 336.96 github-june-2days-2019.json zskp 3 6273951764 537511906 35785 167.20 github-june-2days-2019.json zskp 4 6273951764 518319822 102880 58.16 silesia.tar zskp 1 211947520 73118028 713 283.09 silesia.tar zskp 2 211947520 67504318 1049 192.50 silesia.tar zskp 3 211947520 65102964 2466 81.93 silesia.tar zskp 4 211947520 62790088 8498 23.78 enwik8 zskp 1 100000000 39176328 408 233.17 enwik8 zskp 2 100000000 36036946 623 152.83 enwik8 zskp 3 100000000 33583681 1551 61.47 enwik8 zskp 4 100000000 31601631 4421 21.57 TS40.txt zskp 1 400000000 156408033 1857 205.42 TS40.txt zskp 2 400000000 144331263 2713 140.61 TS40.txt zskp 3 400000000 135435550 5997 63.61 TS40.txt zskp 4 400000000 127882512 18920 20.16 ```
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Add slow compression mode, but with the best compression ratio available
Allows a nice size improvement over "better" mode, but at a significant CPU penalty.
Typical speed is currently around 25MB/s
Some speed examples:
So far fairly naiive implementation, but offers decent improvements.
Longer term it should probably have chaining replace some of the alternative scans. Some contribute very little.