omegadrh
commented
8 years ago The usage info, manpage, README, etc, should probably be updated to include this information, but here's my understanding of the situation as a starting point.
When ZPAQ compression is used, there are actually only three predefined compression models; method 1 and 2 (the "fast" methods) described on the zpaq page apparently aren't available through libzpaq[1]. This leaves us with just methods 3, 4, and 5.
As you noted, the lrzip program requires that the level argument be 1-9; with ZPAQ compression, this gets mapped to libzpaq levels 1-3 in stream.c:184 as compression_level / 4 + 1 (obviously rounded to an integer).
What this ultimately means the 1-9 -L options for lrzip map out accordingly:
| lrzip -L | libzpaq level | zpaq -method equivalent |
|---|---|---|
| 1 | 1 | 3 |
| 2 | 2 | 4 |
| 3 | 2 | 4 |
| 4 | 2 | 4 |
| 5 | 2 | 4 |
| 6 | 3 | 5 |
| 7 | 3 | 5 |
| 8 | 3 | 5 |
| 9 | 3 | 5 |
[1]: From libzpaq.h:457 in the zpaq source code
It does not work with the fast method type arguments to compress() or compressBlock(). Levels 1, 2, and 3 correspond approximately to "3", "4", and "5".
shrx
The help output suggests that we can choose a compression level with
-L #switch when using lzma/bzip2/gzip compression.However,
-Lalso affects the compression level when using the ZPAQ compression with-z. ZPAQ's number of compression levels varies with version number [1]. What ZPAQ compression levels do the lrzip's compression levels 1-9 correspond to?