Comment by aidanhs

First off, I love zstd and thanks for your work - I've used it multiple times with great success.

My question is...what's up with zstd compression levels? It seems to be impossible to find documentation on what the supported compression levels are, and then there are magic numbers that make things more confusing (I think last time I checked, 0 means 'default' which translates to level 3?)

My notes when I was trying to track through the minimum compression level through multiple header files seemed to indicate it's MINCLEVEL...which appears to be -131072? But it starts talking about block sizes and target length, and I'm not entirely sure why they would relate to a compression level.

  # define MINCLEVEL  ZSTD_minCLevel() [0]
  int ZSTD_minCLevel(void) { return (int)-ZSTD_TARGETLENGTH_MAX; } [1]
  #define ZSTD_TARGETLENGTH_MAX    ZSTD_BLOCKSIZE_MAX [2]
  #define ZSTD_BLOCKSIZE_MAX     (1<<ZSTD_BLOCKSIZELOG_MAX) [3]
  #define ZSTD_BLOCKSIZELOG_MAX  17 [3]

[0] https://github.com/facebook/zstd/blob/550410d05d7c7815b1ff41... [1] https://github.com/facebook/zstd/blob/550410d05d7c7815b1ff41... [2] https://github.com/facebook/zstd/blob/550410d05d7c7815b1ff41... [3] https://github.com/facebook/zstd/blob/550410d05d7c7815b1ff41...

Basically, is there a decent reference I can be looking at here?