--- /dev/null
+zstd(1) -- zstd, zstdmt, unzstd, zstdcat - Compress or decompress .zst files
+============================================================================
+
+SYNOPSIS
+--------
+
+`zstd` [<OPTIONS>] [-|<INPUT-FILE>] [-o <OUTPUT-FILE>]
+
+`zstdmt` is equivalent to `zstd -T0`
+
+`unzstd` is equivalent to `zstd -d`
+
+`zstdcat` is equivalent to `zstd -dcf`
+
+
+DESCRIPTION
+-----------
+`zstd` is a fast lossless compression algorithm and data compression tool,
+with command line syntax similar to `gzip`(1) and `xz`(1).
+It is based on the **LZ77** family, with further FSE & huff0 entropy stages.
+`zstd` offers highly configurable compression speed,
+from fast modes at > 200 MB/s per core,
+to strong modes with excellent compression ratios.
+It also features a very fast decoder, with speeds > 500 MB/s per core.
+
+`zstd` command line syntax is generally similar to gzip,
+but features the following differences:
+
+ - Source files are preserved by default.
+ It's possible to remove them automatically by using the `--rm` command.
+ - When compressing a single file, `zstd` displays progress notifications
+ and result summary by default.
+ Use `-q` to turn them off.
+ - `zstd` displays a short help page when command line is an error.
+ Use `-q` to turn it off.
+ - `zstd` does not accept input from console,
+ though it does accept `stdin` when it's not the console.
+ - `zstd` does not store the input's filename or attributes, only its contents.
+
+`zstd` processes each _file_ according to the selected operation mode.
+If no _files_ are given or _file_ is `-`, `zstd` reads from standard input
+and writes the processed data to standard output.
+`zstd` will refuse to write compressed data to standard output
+if it is a terminal: it will display an error message and skip the file.
+Similarly, `zstd` will refuse to read compressed data from standard input
+if it is a terminal.
+
+Unless `--stdout` or `-o` is specified, _files_ are written to a new file
+whose name is derived from the source _file_ name:
+
+* When compressing, the suffix `.zst` is appended to the source filename to
+ get the target filename.
+* When decompressing, the `.zst` suffix is removed from the source filename to
+ get the target filename
+
+### Concatenation with .zst Files
+It is possible to concatenate multiple `.zst` files. `zstd` will decompress
+such agglomerated file as if it was a single `.zst` file.
+
+OPTIONS
+-------
+
+### Integer Suffixes and Special Values
+
+In most places where an integer argument is expected,
+an optional suffix is supported to easily indicate large integers.
+There must be no space between the integer and the suffix.
+
+* `KiB`:
+ Multiply the integer by 1,024 (2\^10).
+ `Ki`, `K`, and `KB` are accepted as synonyms for `KiB`.
+* `MiB`:
+ Multiply the integer by 1,048,576 (2\^20).
+ `Mi`, `M`, and `MB` are accepted as synonyms for `MiB`.
+
+### Operation Mode
+
+If multiple operation mode options are given,
+the last one takes effect.
+
+* `-z`, `--compress`:
+ Compress.
+ This is the default operation mode when no operation mode option is specified
+ and no other operation mode is implied from the command name
+ (for example, `unzstd` implies `--decompress`).
+* `-d`, `--decompress`, `--uncompress`:
+ Decompress.
+* `-t`, `--test`:
+ Test the integrity of compressed _files_.
+ This option is equivalent to `--decompress --stdout > /dev/null`,
+ decompressed data is discarded and checksummed for errors.
+ No files are created or removed.
+* `-b#`:
+ Benchmark file(s) using compression level _#_.
+ See _BENCHMARK_ below for a description of this operation.
+* `--train FILES`:
+ Use _FILES_ as a training set to create a dictionary.
+ The training set should contain a lot of small files (> 100).
+ See _DICTIONARY BUILDER_ below for a description of this operation.
+* `-l`, `--list`:
+ Display information related to a zstd compressed file, such as size, ratio, and checksum.
+ Some of these fields may not be available.
+ This command's output can be augmented with the `-v` modifier.
+
+### Operation Modifiers
+
+* `-#`:
+ selects `#` compression level \[1-19\] (default: 3)
+* `--ultra`:
+ unlocks high compression levels 20+ (maximum 22), using a lot more memory.
+ Note that decompression will also require more memory when using these levels.
+* `--fast[=#]`:
+ switch to ultra-fast compression levels.
+ If `=#` is not present, it defaults to `1`.
+ The higher the value, the faster the compression speed,
+ at the cost of some compression ratio.
+ This setting overwrites compression level if one was set previously.
+ Similarly, if a compression level is set after `--fast`, it overrides it.
+* `-T#`, `--threads=#`:
+ Compress using `#` working threads (default: 1).
+ If `#` is 0, attempt to detect and use the number of physical CPU cores.
+ In all cases, the nb of threads is capped to `ZSTDMT_NBWORKERS_MAX`,
+ which is either 64 in 32-bit mode, or 256 for 64-bit environments.
+ This modifier does nothing if `zstd` is compiled without multithread support.
+* `--single-thread`:
+ Use a single thread for both I/O and compression.
+ As compression is serialized with I/O, this can be slightly slower.
+ Single-thread mode features significantly lower memory usage,
+ which can be useful for systems with limited amount of memory, such as 32-bit systems.
+
+ Note 1: this mode is the only available one when multithread support is disabled.
+
+ Note 2: this mode is different from `-T1`, which spawns 1 compression thread in parallel with I/O.
+ Final compressed result is also slightly different from `-T1`.
+* `--auto-threads={physical,logical} (default: physical)`:
+ When using a default amount of threads via `-T0`, choose the default based on the number
+ of detected physical or logical cores.
+* `--adapt[=min=#,max=#]`:
+ `zstd` will dynamically adapt compression level to perceived I/O conditions.
+ Compression level adaptation can be observed live by using command `-v`.
+ Adaptation can be constrained between supplied `min` and `max` levels.
+ The feature works when combined with multi-threading and `--long` mode.
+ It does not work with `--single-thread`.
+ It sets window size to 8 MiB by default (can be changed manually, see `wlog`).
+ Due to the chaotic nature of dynamic adaptation, compressed result is not reproducible.
+
+ _Note_: at the time of this writing, `--adapt` can remain stuck at low speed
+ when combined with multiple worker threads (>=2).
+* `--long[=#]`:
+ enables long distance matching with `#` `windowLog`, if `#` is not
+ present it defaults to `27`.
+ This increases the window size (`windowLog`) and memory usage for both the
+ compressor and decompressor.
+ This setting is designed to improve the compression ratio for files with
+ long matches at a large distance.
+
+ Note: If `windowLog` is set to larger than 27, `--long=windowLog` or
+ `--memory=windowSize` needs to be passed to the decompressor.
+* `-D DICT`:
+ use `DICT` as Dictionary to compress or decompress FILE(s)
+* `--patch-from FILE`:
+ Specify the file to be used as a reference point for zstd's diff engine.
+ This is effectively dictionary compression with some convenient parameter
+ selection, namely that _windowSize_ > _srcSize_.
+
+ Note: cannot use both this and `-D` together.
+
+ Note: `--long` mode will be automatically activated if _chainLog_ < _fileLog_
+ (_fileLog_ being the _windowLog_ required to cover the whole file). You
+ can also manually force it.
+
+ Note: for all levels, you can use `--patch-from` in `--single-thread` mode
+ to improve compression ratio at the cost of speed.
+
+ Note: for level 19, you can get increased compression ratio at the cost
+ of speed by specifying `--zstd=targetLength=` to be something large
+ (i.e. 4096), and by setting a large `--zstd=chainLog=`.
+* `--rsyncable`:
+ `zstd` will periodically synchronize the compression state to make the
+ compressed file more rsync-friendly.
+ There is a negligible impact to compression ratio,
+ and a potential impact to compression speed, perceptible at higher speeds,
+ for example when combining `--rsyncable` with many parallel worker threads.
+ This feature does not work with `--single-thread`. You probably don't want
+ to use it with long range mode, since it will decrease the effectiveness of
+ the synchronization points, but your mileage may vary.
+* `-C`, `--[no-]check`:
+ add integrity check computed from uncompressed data (default: enabled)
+* `--[no-]content-size`:
+ enable / disable whether or not the original size of the file is placed in
+ the header of the compressed file. The default option is
+ `--content-size` (meaning that the original size will be placed in the header).
+* `--no-dictID`:
+ do not store dictionary ID within frame header (dictionary compression).
+ The decoder will have to rely on implicit knowledge about which dictionary to use,
+ it won't be able to check if it's correct.
+* `-M#`, `--memory=#`:
+ Set a memory usage limit. By default, `zstd` uses 128 MiB for decompression
+ as the maximum amount of memory the decompressor is allowed to use, but you can
+ override this manually if need be in either direction (i.e. you can increase or
+ decrease it).
+
+ This is also used during compression when using with `--patch-from=`. In this case,
+ this parameter overrides that maximum size allowed for a dictionary. (128 MiB).
+
+ Additionally, this can be used to limit memory for dictionary training. This parameter
+ overrides the default limit of 2 GiB. zstd will load training samples up to the memory limit
+ and ignore the rest.
+* `--stream-size=#`:
+ Sets the pledged source size of input coming from a stream. This value must be exact, as it
+ will be included in the produced frame header. Incorrect stream sizes will cause an error.
+ This information will be used to better optimize compression parameters, resulting in
+ better and potentially faster compression, especially for smaller source sizes.
+* `--size-hint=#`:
+ When handling input from a stream, `zstd` must guess how large the source size
+ will be when optimizing compression parameters. If the stream size is relatively
+ small, this guess may be a poor one, resulting in a higher compression ratio than
+ expected. This feature allows for controlling the guess when needed.
+ Exact guesses result in better compression ratios. Overestimates result in slightly
+ degraded compression ratios, while underestimates may result in significant degradation.
+* `-o FILE`:
+ save result into `FILE`.
+* `-f`, `--force`:
+ disable input and output checks. Allows overwriting existing files, input
+ from console, output to stdout, operating on links, block devices, etc.
+ During decompression and when the output destination is stdout, pass-through
+ unrecognized formats as-is.
+* `-c`, `--stdout`:
+ write to standard output (even if it is the console); keep original files unchanged.
+* `--[no-]sparse`:
+ enable / disable sparse FS support,
+ to make files with many zeroes smaller on disk.
+ Creating sparse files may save disk space and speed up decompression by
+ reducing the amount of disk I/O.
+ default: enabled when output is into a file,
+ and disabled when output is stdout.
+ This setting overrides default and can force sparse mode over stdout.
+* `--[no-]pass-through`
+ enable / disable passing through uncompressed files as-is. During
+ decompression when pass-through is enabled, unrecognized formats will be
+ copied as-is from the input to the output. By default, pass-through will
+ occur when the output destination is stdout and the force (`-f`) option is
+ set.
+* `--rm`:
+ remove source file(s) after successful compression or decompression.
+ This command is silently ignored if output is `stdout`.
+ If used in combination with `-o`,
+ triggers a confirmation prompt (which can be silenced with `-f`), as this is a destructive operation.
+* `-k`, `--keep`:
+ keep source file(s) after successful compression or decompression.
+ This is the default behavior.
+* `-r`:
+ operate recursively on directories.
+ It selects all files in the named directory and all its subdirectories.
+ This can be useful both to reduce command line typing,
+ and to circumvent shell expansion limitations,
+ when there are a lot of files and naming breaks the maximum size of a command line.
+* `--filelist FILE`
+ read a list of files to process as content from `FILE`.
+ Format is compatible with `ls` output, with one file per line.
+* `--output-dir-flat DIR`:
+ resulting files are stored into target `DIR` directory,
+ instead of same directory as origin file.
+ Be aware that this command can introduce name collision issues,
+ if multiple files, from different directories, end up having the same name.
+ Collision resolution ensures first file with a given name will be present in `DIR`,
+ while in combination with `-f`, the last file will be present instead.
+* `--output-dir-mirror DIR`:
+ similar to `--output-dir-flat`,
+ the output files are stored underneath target `DIR` directory,
+ but this option will replicate input directory hierarchy into output `DIR`.
+
+ If input directory contains "..", the files in this directory will be ignored.
+ If input directory is an absolute directory (i.e. "/var/tmp/abc"),
+ it will be stored into the "output-dir/var/tmp/abc".
+ If there are multiple input files or directories,
+ name collision resolution will follow the same rules as `--output-dir-flat`.
+* `--format=FORMAT`:
+ compress and decompress in other formats. If compiled with
+ support, zstd can compress to or decompress from other compression algorithm
+ formats. Possibly available options are `zstd`, `gzip`, `xz`, `lzma`, and `lz4`.
+ If no such format is provided, `zstd` is the default.
+* `-h`/`-H`, `--help`:
+ display help/long help and exit
+* `-V`, `--version`:
+ display version number and exit.
+ Advanced: `-vV` also displays supported formats.
+ `-vvV` also displays POSIX support.
+ `-q` will only display the version number, suitable for machine reading.
+* `-v`, `--verbose`:
+ verbose mode, display more information
+* `-q`, `--quiet`:
+ suppress warnings, interactivity, and notifications.
+ specify twice to suppress errors too.
+* `--no-progress`:
+ do not display the progress bar, but keep all other messages.
+* `--show-default-cparams`:
+ shows the default compression parameters that will be used for a particular input file, based on the provided compression level and the input size.
+ If the provided file is not a regular file (e.g. a pipe), this flag will output the parameters used for inputs of unknown size.
+* `--`:
+ All arguments after `--` are treated as files
+
+
+### gzip Operation Modifiers
+When invoked via a `gzip` symlink, `zstd` will support further
+options that intend to mimic the `gzip` behavior:
+
+* `-n`, `--no-name`:
+ do not store the original filename and timestamps when compressing
+ a file. This is the default behavior and hence a no-op.
+* `--best`:
+ alias to the option `-9`.
+
+
+### Environment Variables
+
+Employing environment variables to set parameters has security implications.
+Therefore, this avenue is intentionally limited.
+Only `ZSTD_CLEVEL` and `ZSTD_NBTHREADS` are currently supported.
+They set the compression level and number of threads to use during compression, respectively.
+
+`ZSTD_CLEVEL` can be used to set the level between 1 and 19 (the "normal" range).
+If the value of `ZSTD_CLEVEL` is not a valid integer, it will be ignored with a warning message.
+`ZSTD_CLEVEL` just replaces the default compression level (`3`).
+
+`ZSTD_NBTHREADS` can be used to set the number of threads `zstd` will attempt to use during compression.
+If the value of `ZSTD_NBTHREADS` is not a valid unsigned integer, it will be ignored with a warning message.
+`ZSTD_NBTHREADS` has a default value of (`1`), and is capped at ZSTDMT_NBWORKERS_MAX==200.
+`zstd` must be compiled with multithread support for this to have any effect.
+
+They can both be overridden by corresponding command line arguments:
+`-#` for compression level and `-T#` for number of compression threads.
+
+
+DICTIONARY BUILDER
+------------------
+`zstd` offers _dictionary_ compression,
+which greatly improves efficiency on small files and messages.
+It's possible to train `zstd` with a set of samples,
+the result of which is saved into a file called a `dictionary`.
+Then, during compression and decompression, reference the same dictionary,
+using command `-D dictionaryFileName`.
+Compression of small files similar to the sample set will be greatly improved.
+
+* `--train FILEs`:
+ Use FILEs as training set to create a dictionary.
+ The training set should ideally contain a lot of samples (> 100),
+ and weight typically 100x the target dictionary size
+ (for example, ~10 MB for a 100 KB dictionary).
+ `--train` can be combined with `-r` to indicate a directory rather than listing all the files,
+ which can be useful to circumvent shell expansion limits.
+
+ Since dictionary compression is mostly effective for small files,
+ the expectation is that the training set will only contain small files.
+ In the case where some samples happen to be large,
+ only the first 128 KiB of these samples will be used for training.
+
+ `--train` supports multithreading if `zstd` is compiled with threading support (default).
+ Additional advanced parameters can be specified with `--train-fastcover`.
+ The legacy dictionary builder can be accessed with `--train-legacy`.
+ The slower cover dictionary builder can be accessed with `--train-cover`.
+ Default `--train` is equivalent to `--train-fastcover=d=8,steps=4`.
+
+* `-o FILE`:
+ Dictionary saved into `FILE` (default name: dictionary).
+* `--maxdict=#`:
+ Limit dictionary to specified size (default: 112640 bytes).
+ As usual, quantities are expressed in bytes by default,
+ and it's possible to employ suffixes (like `KB` or `MB`)
+ to specify larger values.
+* `-#`:
+ Use `#` compression level during training (optional).
+ Will generate statistics more tuned for selected compression level,
+ resulting in a _small_ compression ratio improvement for this level.
+* `-B#`:
+ Split input files into blocks of size # (default: no split)
+* `-M#`, `--memory=#`:
+ Limit the amount of sample data loaded for training (default: 2 GB).
+ Note that the default (2 GB) is also the maximum.
+ This parameter can be useful in situations where the training set size
+ is not well controlled and could be potentially very large.
+ Since speed of the training process is directly correlated to
+ the size of the training sample set,
+ a smaller sample set leads to faster training.
+
+ In situations where the training set is larger than maximum memory,
+ the CLI will randomly select samples among the available ones,
+ up to the maximum allowed memory budget.
+ This is meant to improve dictionary relevance
+ by mitigating the potential impact of clustering,
+ such as selecting only files from the beginning of a list
+ sorted by modification date, or sorted by alphabetical order.
+ The randomization process is deterministic, so
+ training of the same list of files with the same parameters
+ will lead to the creation of the same dictionary.
+
+* `--dictID=#`:
+ A dictionary ID is a locally unique ID.
+ The decoder will use this value to verify it is using the right dictionary.
+ By default, zstd will create a 4-bytes random number ID.
+ It's possible to provide an explicit number ID instead.
+ It's up to the dictionary manager to not assign twice the same ID to
+ 2 different dictionaries.
+ Note that short numbers have an advantage:
+ an ID < 256 will only need 1 byte in the compressed frame header,
+ and an ID < 65536 will only need 2 bytes.
+ This compares favorably to 4 bytes default.
+
+ Note that RFC8878 reserves IDs less than 32768 and greater than or equal to 2\^31, so they should not be used in public.
+
+* `--train-cover[=k#,d=#,steps=#,split=#,shrink[=#]]`:
+ Select parameters for the default dictionary builder algorithm named cover.
+ If _d_ is not specified, then it tries _d_ = 6 and _d_ = 8.
+ If _k_ is not specified, then it tries _steps_ values in the range [50, 2000].
+ If _steps_ is not specified, then the default value of 40 is used.
+ If _split_ is not specified or split <= 0, then the default value of 100 is used.
+ Requires that _d_ <= _k_.
+ If _shrink_ flag is not used, then the default value for _shrinkDict_ of 0 is used.
+ If _shrink_ is not specified, then the default value for _shrinkDictMaxRegression_ of 1 is used.
+
+ Selects segments of size _k_ 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 _d_.
+ Generally _d_ should be in the range [6, 8], occasionally up to 16, but the
+ algorithm will run faster with d <= _8_.
+ Good values for _k_ vary widely based on the input data, but a safe range is
+ [2 * _d_, 2000].
+ If _split_ is 100, all input samples are used for both training and testing
+ to find optimal _d_ and _k_ to build dictionary.
+ Supports multithreading if `zstd` is compiled with threading support.
+ Having _shrink_ enabled takes a truncated dictionary of minimum size and doubles
+ in size until compression ratio of the truncated dictionary is at most
+ _shrinkDictMaxRegression%_ worse than the compression ratio of the largest dictionary.
+
+ Examples:
+
+ `zstd --train-cover FILEs`
+
+ `zstd --train-cover=k=50,d=8 FILEs`
+
+ `zstd --train-cover=d=8,steps=500 FILEs`
+
+ `zstd --train-cover=k=50 FILEs`
+
+ `zstd --train-cover=k=50,split=60 FILEs`
+
+ `zstd --train-cover=shrink FILEs`
+
+ `zstd --train-cover=shrink=2 FILEs`
+
+* `--train-fastcover[=k#,d=#,f=#,steps=#,split=#,accel=#]`:
+ Same as cover but with extra parameters _f_ and _accel_ and different default value of split
+ If _split_ is not specified, then it tries _split_ = 75.
+ If _f_ is not specified, then it tries _f_ = 20.
+ Requires that 0 < _f_ < 32.
+ If _accel_ is not specified, then it tries _accel_ = 1.
+ Requires that 0 < _accel_ <= 10.
+ Requires that _d_ = 6 or _d_ = 8.
+
+ _f_ is log of size of array that keeps track of frequency of subsegments of size _d_.
+ The subsegment is hashed to an index in the range [0,2^_f_ - 1].
+ It is possible that 2 different subsegments are hashed to the same index, and they are considered as the same subsegment when computing frequency.
+ Using a higher _f_ reduces collision but takes longer.
+
+ Examples:
+
+ `zstd --train-fastcover FILEs`
+
+ `zstd --train-fastcover=d=8,f=15,accel=2 FILEs`
+
+* `--train-legacy[=selectivity=#]`:
+ Use legacy dictionary builder algorithm with the given dictionary
+ _selectivity_ (default: 9).
+ The smaller the _selectivity_ value, the denser the dictionary,
+ improving its efficiency but reducing its achievable maximum size.
+ `--train-legacy=s=#` is also accepted.
+
+ Examples:
+
+ `zstd --train-legacy FILEs`
+
+ `zstd --train-legacy=selectivity=8 FILEs`
+
+
+BENCHMARK
+---------
+
+* `-b#`:
+ benchmark file(s) using compression level #
+* `-e#`:
+ benchmark file(s) using multiple compression levels, from `-b#` to `-e#` (inclusive)
+* `-i#`:
+ minimum evaluation time, in seconds (default: 3s), benchmark mode only
+* `-B#`, `--block-size=#`:
+ cut file(s) into independent chunks of size # (default: no chunking)
+* `--priority=rt`:
+ set process priority to real-time
+
+**Output Format:** CompressionLevel#Filename: InputSize -> OutputSize (CompressionRatio), CompressionSpeed, DecompressionSpeed
+
+**Methodology:** 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 order to improve measurement accuracy.
+
+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 depending on compression level (generally `4 * windowSize`).
+`-B#` makes it possible to manually select a custom size.
+Note that job size must respect a minimum value which is enforced transparently.
+This minimum is either 512 KB, or `overlapSize`, whichever is largest.
+Different job sizes will lead to non-identical compressed frames.
+
+### --zstd[=options]:
+`zstd` 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 this translation with `--show-default-cparams`.)
+These specific parameters can be overridden with advanced compression options.
+The _options_ are provided as a comma-separated list.
+You may specify only the options you want to change and the rest will be
+taken from the selected or default compression level.
+The list of available _options_:
+
+- `strategy`=_strat_, `strat`=_strat_:
+ Specify a strategy used by a match finder.
+
+ There are 9 strategies numbered from 1 to 9, from fastest to strongest:
+ 1=`ZSTD_fast`, 2=`ZSTD_dfast`, 3=`ZSTD_greedy`,
+ 4=`ZSTD_lazy`, 5=`ZSTD_lazy2`, 6=`ZSTD_btlazy2`,
+ 7=`ZSTD_btopt`, 8=`ZSTD_btultra`, 9=`ZSTD_btultra2`.
+
+- `windowLog`=_wlog_, `wlog`=_wlog_:
+ Specify the maximum number of bits for a match distance.
+
+ 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 _wlog_ is 10 (1 KiB) and the maximum is 30 (1 GiB) on 32-bit
+ platforms and 31 (2 GiB) on 64-bit platforms.
+
+ Note: If `windowLog` is set to larger than 27, `--long=windowLog` or
+ `--memory=windowSize` needs to be passed to the decompressor.
+
+- `hashLog`=_hlog_, `hlog`=_hlog_:
+ Specify the maximum number of bits for a hash table.
+
+ Bigger hash tables cause fewer collisions which usually makes compression
+ faster, but requires more memory during compression.
+
+ The minimum _hlog_ is 6 (64 entries / 256 B) and the maximum is 30 (1B entries / 4 GiB).
+
+- `chainLog`=_clog_, `clog`=_clog_:
+ Specify the maximum number of bits for the secondary search structure,
+ whose form depends on the selected `strategy`.
+
+ 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 `ZSTD_fast` `strategy`, which only has the primary hash table.
+
+ The minimum _clog_ 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.
+
+- `searchLog`=_slog_, `slog`=_slog_:
+ Specify the maximum number of searches in a hash chain or a binary tree
+ using logarithmic scale.
+
+ More searches increases the chance to find a match which usually increases
+ compression ratio but decreases compression speed.
+
+ The minimum _slog_ is 1 and the maximum is 'windowLog' - 1.
+
+- `minMatch`=_mml_, `mml`=_mml_:
+ Specify the minimum searched length of a match in a hash table.
+
+ Larger search lengths usually decrease compression ratio but improve
+ decompression speed.
+
+ The minimum _mml_ is 3 and the maximum is 7.
+
+- `targetLength`=_tlen_, `tlen`=_tlen_:
+ The impact of this field vary depending on selected strategy.
+
+ For `ZSTD_btopt`, `ZSTD_btultra` and `ZSTD_btultra2`, it specifies
+ the minimum match length that causes match finder to stop searching.
+ A larger `targetLength` usually improves compression ratio
+ but decreases compression speed.
+
+ For `ZSTD_fast`, it triggers ultra-fast mode when > 0.
+ The value represents the amount of data skipped between match sampling.
+ Impact is reversed: a larger `targetLength` increases compression speed
+ but decreases compression ratio.
+
+ For all other strategies, this field has no impact.
+
+ The minimum _tlen_ is 0 and the maximum is 128 KiB.
+
+- `overlapLog`=_ovlog_, `ovlog`=_ovlog_:
+ Determine `overlapSize`, 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.
+
+ The minimum _ovlog_ is 0, and the maximum is 9.
+ 1 means "no overlap", hence completely independent jobs.
+ 9 means "full overlap", meaning up to `windowSize` is reloaded from previous job.
+ Reducing _ovlog_ by 1 reduces the reloaded amount by a factor 2.
+ For example, 8 means "windowSize/2", and 6 means "windowSize/8".
+ Value 0 is special and means "default": _ovlog_ is automatically determined by `zstd`.
+ In which case, _ovlog_ will range from 6 to 9, depending on selected _strat_.
+
+- `ldmHashLog`=_lhlog_, `lhlog`=_lhlog_:
+ Specify the maximum size for a hash table used for long distance matching.
+
+ This option is ignored unless long distance matching is enabled.
+
+ Bigger hash tables usually improve compression ratio at the expense of more
+ memory during compression and a decrease in compression speed.
+
+ The minimum _lhlog_ is 6 and the maximum is 30 (default: 20).
+
+- `ldmMinMatch`=_lmml_, `lmml`=_lmml_:
+ Specify the minimum searched length of a match for long distance matching.
+
+ This option is ignored unless long distance matching is enabled.
+
+ Larger/very small values usually decrease compression ratio.
+
+ The minimum _lmml_ is 4 and the maximum is 4096 (default: 64).
+
+- `ldmBucketSizeLog`=_lblog_, `lblog`=_lblog_:
+ Specify the size of each bucket for the hash table used for long distance
+ matching.
+
+ This option is ignored unless long distance matching is enabled.
+
+ Larger bucket sizes improve collision resolution but decrease compression
+ speed.
+
+ The minimum _lblog_ is 1 and the maximum is 8 (default: 3).
+
+- `ldmHashRateLog`=_lhrlog_, `lhrlog`=_lhrlog_:
+ Specify the frequency of inserting entries into the long distance matching
+ hash table.
+
+ This option is ignored unless long distance matching is enabled.
+
+ Larger values will improve compression speed. Deviating far from the
+ default value will likely result in a decrease in compression ratio.
+
+ The default value is `wlog - lhlog`.
+
+### Example
+The following parameters sets advanced compression options to something
+similar to predefined level 19 for files bigger than 256 KB:
+
+`--zstd`=wlog=23,clog=23,hlog=22,slog=6,mml=3,tlen=48,strat=6
+
+SEE ALSO
+--------
+`zstdgrep`(1), `zstdless`(1), `gzip`(1), `xz`(1)
+
+The <zstandard> format is specified in Y. Collet, "Zstandard Compression and the 'application/zstd' Media Type", https://www.ietf.org/rfc/rfc8878.txt, Internet RFC 8878 (February 2021).
+
+BUGS
+----
+Report bugs at: https://github.com/facebook/zstd/issues
+
+AUTHOR
+------
+Yann Collet
notaz.gp2x.de / pcsx_rearmed.git / blobdiff