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Select parameters for the default dictionary builder algorithm named cover\. If \fId\fR is not specified, then it tries \fId\fR = 6 and \fId\fR = 8\. If \fIk\fR is not specified, then it tries \fIsteps\fR values in the range [50, 2000]\. If \fIsteps\...
.IP
Selects segments of size \fIk\fR with highest score to put in the dictionary\. The score of a segment is computed by the sum of the frequencies of all the subsegments of size \fId\fR\. Generally \fId\fR should be in the range [6, 8], occasionally up ...
.IP
Examples:
.IP
\fBzstd \-\-train\-cover FILEs\fR
.IP
\fBzstd \-\-train\-cover=k=50,d=8 FILEs\fR
.IP
\fBzstd \-\-train\-cover=d=8,steps=500 FILEs\fR
.IP
\fBzstd \-\-train\-cover=k=50 FILEs\fR
.IP
\fBzstd \-\-train\-cover=k=50,split=60 FILEs\fR
.IP
\fBzstd \-\-train\-cover=shrink FILEs\fR
.IP
\fBzstd \-\-train\-cover=shrink=2 FILEs\fR
.TP
\fB\-\-train\-fastcover[=k#,d=#,f=#,steps=#,split=#,accel=#]\fR
Same as cover but with extra parameters \fIf\fR and \fIaccel\fR and different default value of split If \fIsplit\fR is not specified, then it tries \fIsplit\fR = 75\. If \fIf\fR is not specified, then it tries \fIf\fR = 20\. Requires that 0 < \fIf\fR...
.IP
\fIf\fR is log of size of array that keeps track of frequency of subsegments of size \fId\fR\. The subsegment is hashed to an index in the range [0,2^\fIf\fR \- 1]\. It is possible that 2 different subsegments are hashed to the same index, and they a...
.IP
Examples:
.IP
\fBzstd \-\-train\-fastcover FILEs\fR
.IP
\fBzstd \-\-train\-fastcover=d=8,f=15,accel=2 FILEs\fR
.TP
\fB\-\-train\-legacy[=selectivity=#]\fR
Use legacy dictionary builder algorithm with the given dictionary \fIselectivity\fR (default: 9)\. The smaller the \fIselectivity\fR value, the denser the dictionary, improving its efficiency but reducing its achievable maximum size\. \fB\-\-train\-l...
.IP
Examples:
.IP
\fBzstd \-\-train\-legacy FILEs\fR
.IP
\fBzstd \-\-train\-legacy=selectivity=8 FILEs\fR
.SH "BENCHMARK"
.TP
\fB\-b#\fR
benchmark file(s) using compression level #
.TP
\fB\-e#\fR
benchmark file(s) using multiple compression levels, from \fB\-b#\fR to \fB\-e#\fR (inclusive)
.TP
\fB\-i#\fR
minimum evaluation time, in seconds (default: 3s), benchmark mode only
.TP
\fB\-B#\fR, \fB\-\-block\-size=#\fR
cut file(s) into independent chunks of size # (default: no chunking)
.TP
\fB\-\-priority=rt\fR
set process priority to real\-time
.P
\fBOutput Format:\fR CompressionLevel#Filename: InputSize \-> OutputSize (CompressionRatio), CompressionSpeed, DecompressionSpeed
.P
\fBMethodology:\fR For both compression and decompression speed, the entire input is compressed/decompressed in\-memory to measure speed\. A run lasts at least 1 sec, so when files are small, they are compressed/decompressed several times per run, in...
.SH "ADVANCED COMPRESSION OPTIONS"
### \-B#: Specify the size of each compression job\. This parameter is only available when multi\-threading is enabled\. Each compression job is run in parallel, so this value indirectly impacts the nb of active threads\. Default job size varies depe...
.SS "\-\-zstd[=options]:"
\fBzstd\fR provides 22 predefined regular compression levels plus the fast levels\. This compression level is translated internally into a number of specific parameters that actually control the behavior of the compressor\. (You can see the result of...
.TP
\fBstrategy\fR=\fIstrat\fR, \fBstrat\fR=\fIstrat\fR
Specify a strategy used by a match finder\.
.IP
There are 9 strategies numbered from 1 to 9, from fastest to strongest: 1=\fBZSTD_fast\fR, 2=\fBZSTD_dfast\fR, 3=\fBZSTD_greedy\fR, 4=\fBZSTD_lazy\fR, 5=\fBZSTD_lazy2\fR, 6=\fBZSTD_btlazy2\fR, 7=\fBZSTD_btopt\fR, 8=\fBZSTD_btultra\fR, 9=\fBZSTD_btult...
.TP
\fBwindowLog\fR=\fIwlog\fR, \fBwlog\fR=\fIwlog\fR
Specify the maximum number of bits for a match distance\.
.IP
The higher number of increases the chance to find a match which usually improves compression ratio\. It also increases memory requirements for the compressor and decompressor\. The minimum \fIwlog\fR is 10 (1 KiB) and the maximum is 30 (1 GiB) on 32\...
.IP
Note: If \fBwindowLog\fR is set to larger than 27, \fB\-\-long=windowLog\fR or \fB\-\-memory=windowSize\fR needs to be passed to the decompressor\.
.TP
\fBhashLog\fR=\fIhlog\fR, \fBhlog\fR=\fIhlog\fR
Specify the maximum number of bits for a hash table\.
.IP
Bigger hash tables cause fewer collisions which usually makes compression faster, but requires more memory during compression\.
.IP
The minimum \fIhlog\fR is 6 (64 entries / 256 B) and the maximum is 30 (1B entries / 4 GiB)\.
.TP
\fBchainLog\fR=\fIclog\fR, \fBclog\fR=\fIclog\fR
Specify the maximum number of bits for the secondary search structure, whose form depends on the selected \fBstrategy\fR\.
.IP
Higher numbers of bits increases the chance to find a match which usually improves compression ratio\. It also slows down compression speed and increases memory requirements for compression\. This option is ignored for the \fBZSTD_fast\fR \fBstrategy...
.IP
The minimum \fIclog\fR is 6 (64 entries / 256 B) and the maximum is 29 (512M entries / 2 GiB) on 32\-bit platforms and 30 (1B entries / 4 GiB) on 64\-bit platforms\.
.TP
\fBsearchLog\fR=\fIslog\fR, \fBslog\fR=\fIslog\fR
Specify the maximum number of searches in a hash chain or a binary tree using logarithmic scale\.
.IP
More searches increases the chance to find a match which usually increases compression ratio but decreases compression speed\.
.IP
The minimum \fIslog\fR is 1 and the maximum is \'windowLog\' \- 1\.
.TP
\fBminMatch\fR=\fImml\fR, \fBmml\fR=\fImml\fR
Specify the minimum searched length of a match in a hash table\.
.IP
Larger search lengths usually decrease compression ratio but improve decompression speed\.
.IP
The minimum \fImml\fR is 3 and the maximum is 7\.
.TP
\fBtargetLength\fR=\fItlen\fR, \fBtlen\fR=\fItlen\fR
The impact of this field vary depending on selected strategy\.
.IP
For \fBZSTD_btopt\fR, \fBZSTD_btultra\fR and \fBZSTD_btultra2\fR, it specifies the minimum match length that causes match finder to stop searching\. A larger \fBtargetLength\fR usually improves compression ratio but decreases compression speed\.
.IP
For \fBZSTD_fast\fR, it triggers ultra\-fast mode when > 0\. The value represents the amount of data skipped between match sampling\. Impact is reversed: a larger \fBtargetLength\fR increases compression speed but decreases compression ratio\.
.IP
For all other strategies, this field has no impact\.
.IP
The minimum \fItlen\fR is 0 and the maximum is 128 KiB\.
.TP
\fBoverlapLog\fR=\fIovlog\fR, \fBovlog\fR=\fIovlog\fR
Determine \fBoverlapSize\fR, amount of data reloaded from previous job\. This parameter is only available when multithreading is enabled\. Reloading more data improves compression ratio, but decreases speed\.
.IP
The minimum \fIovlog\fR is 0, and the maximum is 9\. 1 means "no overlap", hence completely independent jobs\. 9 means "full overlap", meaning up to \fBwindowSize\fR is reloaded from previous job\. Reducing \fIovlog\fR by 1 reduces the reloaded amoun...
.TP
\fBldmHashLog\fR=\fIlhlog\fR, \fBlhlog\fR=\fIlhlog\fR