fix: README -> README.md
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ta6ob/lz4/programs/lz4.1.md
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ta6ob/lz4/programs/lz4.1.md
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lz4(1) -- lz4, unlz4, lz4cat - Compress or decompress .lz4 files
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================================================================
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SYNOPSIS
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--------
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`lz4` [*OPTIONS*] [-|INPUT-FILE] <OUTPUT-FILE>
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`unlz4` is equivalent to `lz4 -d`
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`lz4cat` is equivalent to `lz4 -dcfm`
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When writing scripts that need to decompress files,
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it is recommended to always use the name `lz4` with appropriate arguments
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(`lz4 -d` or `lz4 -dc`) instead of the names `unlz4` and `lz4cat`.
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DESCRIPTION
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-----------
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`lz4` is an extremely fast lossless compression algorithm,
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based on **byte-aligned LZ77** family of compression scheme.
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`lz4` offers compression speeds of 400 MB/s per core, linearly scalable with
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multi-core CPUs.
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It features an extremely fast decoder, with speed in multiple GB/s per core,
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typically reaching RAM speed limit on multi-core systems.
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The native file format is the `.lz4` format.
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### Difference between lz4 and gzip
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`lz4` supports a command line syntax similar _but not identical_ to `gzip(1)`.
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Differences are :
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* `lz4` compresses a single file by default (see `-m` for multiple files)
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* `lz4 file1 file2` means : compress file1 _into_ file2
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* `lz4 file.lz4` will default to decompression (use `-z` to force compression)
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* `lz4` preserves original files
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* `lz4` shows real-time notification statistics
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during compression or decompression of a single file
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(use `-q` to silence them)
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* When no destination is specified, result is sent on implicit output,
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which depends on `stdout` status.
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When `stdout` _is Not the console_, it becomes the implicit output.
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Otherwise, if `stdout` is the console, the implicit output is `filename.lz4`.
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* It is considered bad practice to rely on implicit output in scripts.
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because the script's environment may change.
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Always use explicit output in scripts.
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`-c` ensures that output will be `stdout`.
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Conversely, providing a destination name, or using `-m`
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ensures that the output will be either the specified name, or `filename.lz4` respectively.
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Default behaviors can be modified by opt-in commands, detailed below.
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* `lz4 -m` makes it possible to provide multiple input filenames,
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which will be compressed into files using suffix `.lz4`.
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Progress notifications become disabled by default (use `-v` to enable them).
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This mode has a behavior which more closely mimics `gzip` command line,
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with the main remaining difference being that source files are preserved by default.
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* Similarly, `lz4 -m -d` can decompress multiple `*.lz4` files.
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* It's possible to opt-in to erase source files
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on successful compression or decompression, using `--rm` command.
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* Consequently, `lz4 -m --rm` behaves the same as `gzip`.
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### Concatenation of .lz4 files
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It is possible to concatenate `.lz4` files as is.
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`lz4` will decompress such files as if they were a single `.lz4` file.
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For example:
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lz4 file1 > foo.lz4
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lz4 file2 >> foo.lz4
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Then `lz4cat foo.lz4` is equivalent to `cat file1 file2`.
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OPTIONS
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-------
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### Short commands concatenation
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In some cases, some options can be expressed using short command `-x`
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or long command `--long-word`.
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Short commands can be concatenated together.
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For example, `-d -c` is equivalent to `-dc`.
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Long commands cannot be concatenated. They must be clearly separated by a space.
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### Multiple commands
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When multiple contradictory commands are issued on a same command line,
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only the latest one will be applied.
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### Operation mode
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* `-z` `--compress`:
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Compress.
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This is the default operation mode when no operation mode option is
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specified, no other operation mode is implied from the command name
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(for example, `unlz4` implies `--decompress`),
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nor from the input file name
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(for example, a file extension `.lz4` implies `--decompress` by default).
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`-z` can also be used to force compression of an already compressed
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`.lz4` file.
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* `-d` `--decompress` `--uncompress`:
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Decompress.
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`--decompress` is also the default operation when the input filename has an
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`.lz4` extension.
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* `-t` `--test`:
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Test the integrity of compressed `.lz4` files.
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The decompressed data is discarded.
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No files are created nor removed.
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* `-b#`:
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Benchmark mode, using `#` compression level.
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* `--list`:
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List information about .lz4 files.
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note : current implementation is limited to single-frame .lz4 files.
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### Operation modifiers
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* `-#`:
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Compression level, with # being any value from 1 to 12.
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Higher values trade compression speed for compression ratio.
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Values above 12 are considered the same as 12.
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Recommended values are 1 for fast compression (default),
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and 9 for high compression.
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Speed/compression trade-off will vary depending on data to compress.
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Decompression speed remains fast at all settings.
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* `--fast[=#]`:
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Switch to ultra-fast compression levels.
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The higher the value, the faster the compression speed, at the cost of some compression ratio.
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If `=#` is not present, it defaults to `1`.
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This setting overrides compression level if one was set previously.
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Similarly, if a compression level is set after `--fast`, it overrides it.
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* `--best`:
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Set highest compression level. Same as -12.
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* `--favor-decSpeed`:
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Generate compressed data optimized for decompression speed.
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Compressed data will be larger as a consequence (typically by ~0.5%),
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while decompression speed will be improved by 5-20%, depending on use cases.
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This option only works in combination with very high compression levels (>=10).
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* `-D dictionaryName`:
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Compress, decompress or benchmark using dictionary _dictionaryName_.
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Compression and decompression must use the same dictionary to be compatible.
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Using a different dictionary during decompression will either
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abort due to decompression error, or generate a checksum error.
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* `-f` `--[no-]force`:
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This option has several effects:
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If the target file already exists, overwrite it without prompting.
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When used with `--decompress` and `lz4` cannot recognize the type of
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the source file, copy the source file as is to standard output.
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This allows `lz4cat --force` to be used like `cat (1)` for files
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that have not been compressed with `lz4`.
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* `-c` `--stdout` `--to-stdout`:
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Force write to standard output, even if it is the console.
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* `-m` `--multiple`:
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Multiple input files.
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Compressed file names will be appended a `.lz4` suffix.
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This mode also reduces notification level.
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Can also be used to list multiple files.
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`lz4 -m` has a behavior equivalent to `gzip -k`
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(it preserves source files by default).
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* `-r` :
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operate recursively on directories.
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This mode also sets `-m` (multiple input files).
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* `-B#`:
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Block size \[4-7\](default : 7)<br/>
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`-B4`= 64KB ; `-B5`= 256KB ; `-B6`= 1MB ; `-B7`= 4MB
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* `-BI`:
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Produce independent blocks (default)
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* `-BD`:
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Blocks depend on predecessors (improves compression ratio, more noticeable on small blocks)
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* `--[no-]frame-crc`:
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Select frame checksum (default:enabled)
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* `--[no-]content-size`:
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Header includes original size (default:not present)<br/>
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Note : this option can only be activated when the original size can be
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determined, hence for a file. It won't work with unknown source size,
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such as stdin or pipe.
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* `--[no-]sparse`:
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Sparse mode support (default:enabled on file, disabled on stdout)
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* `-l`:
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Use Legacy format (typically for Linux Kernel compression)<br/>
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Note : `-l` is not compatible with `-m` (`--multiple`) nor `-r`
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### Other options
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* `-v` `--verbose`:
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Verbose mode
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* `-q` `--quiet`:
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Suppress warnings and real-time statistics;
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specify twice to suppress errors too
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* `-h` `-H` `--help`:
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Display help/long help and exit
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* `-V` `--version`:
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Display Version number and exit
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* `-k` `--keep`:
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Preserve source files (default behavior)
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* `--rm` :
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Delete source files on successful compression or decompression
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* `--` :
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Treat all subsequent arguments as files
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### Benchmark mode
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* `-b#`:
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Benchmark file(s), using # compression level
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* `-e#`:
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Benchmark multiple compression levels, from b# to e# (included)
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* `-i#`:
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Minimum evaluation time in seconds \[1-9\] (default : 3)
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BUGS
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----
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Report bugs at: https://github.com/lz4/lz4/issues
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AUTHOR
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------
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Yann Collet
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