What we pass to ZSTD Backend

ZSTD gets a level and a strategy

When the -Z|--zstd option is selected, zstd is assigned both a compression level, which is 1-22, and a strategy, which is 1-9. The following settings will be used per compression level -L#.

lrzip-next compression level	zstd compression level	zstd strategy
1	2	ZSTD_fast (1)
2	4	ZSTD_dfast (2)
3	5	ZSTD_greedy (3)
4	7	ZSTD_lazy (4)
5	12	ZSTD_lazy2 (5)
6	15	ZSTD_btlazy2 (6)
7	17	ZSTD_btopt (7)
8	18	ZSTD_btultra (8)
9	22	ZSTD_btultra2 (9)

ZSTD level can be set independently

There is an option --zstd_level which can be used to independently set the zstd level. The zstd strategy is set according to the above mapping automatically. When --zstd_level is used, the -R (for rzip level) option can be set independently for pre-processing. If not, the rzip compression level will be equal to the zstd strategy (1-9).

zstd level	zstd strategy	rzip level
1,2	ZSTD_fast (1)	1
3,4	ZSTD_dfast (2)	2
5	ZSTD_greedy (3)	3
6,7	ZSTD_lazy (4)	4
8-12	ZSTD_lazy2 (5)	5
13-15	ZSTD_btlazy2 (6)	6
16,17	ZSTD_btopt (7)	7
18	ZSTD_btultra (8)	8
19-22	ZSTD_btultra2 (9)	9