Adding upstream version 16.2.11+ds.upstream/16.2.11+dsupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+Command Line Interface for Zstandard library
+============================================
+
+Command Line Interface (CLI) can be created using the `make` command without any additional parameters.
+There are however other Makefile targets that create different variations of CLI:
+- `zstd` : default CLI supporting gzip-like arguments; includes dictionary builder, benchmark, and support for decompression of legacy zstd formats
+- `zstd_nolegacy` : Same as `zstd` but without support for legacy zstd formats
+- `zstd-small` : CLI optimized for minimal size; no dictionary builder, no benchmark, and no support for legacy zstd formats
+- `zstd-compress` : version of CLI which can only compress into zstd format
+- `zstd-decompress` : version of CLI which can only decompress zstd format
+
+
+### Compilation variables
+`zstd` scope can be altered by modifying the following `make` variables :
+
+- __HAVE_THREAD__ : multithreading is automatically enabled when `pthread` is detected.
+  It's possible to disable multithread support, by setting `HAVE_THREAD=0`.
+  Example : `make zstd HAVE_THREAD=0`
+  It's also possible to force multithread support, using `HAVE_THREAD=1`.
+  In which case, linking stage will fail if neither `pthread` nor `windows.h` library can be found.
+  This is useful to ensure this feature is not silently disabled.
+
+- __ZSTD_LEGACY_SUPPORT__ : `zstd` can decompress files compressed by older versions of `zstd`.
+  Starting v0.8.0, all versions of `zstd` produce frames compliant with the [specification](../doc/zstd_compression_format.md), and are therefore compatible.
+  But older versions (< v0.8.0) produced different, incompatible, frames.
+  By default, `zstd` supports decoding legacy formats >= v0.4.0 (`ZSTD_LEGACY_SUPPORT=4`).
+  This can be altered by modifying this compilation variable.
+  `ZSTD_LEGACY_SUPPORT=1` means "support all formats >= v0.1.0".
+  `ZSTD_LEGACY_SUPPORT=2` means "support all formats >= v0.2.0", and so on.
+  `ZSTD_LEGACY_SUPPORT=0` means _DO NOT_ support any legacy format.
+  if `ZSTD_LEGACY_SUPPORT >= 8`, it's the same as `0`, since there is no legacy format after `7`.
+  Note : `zstd` only supports decoding older formats, and cannot generate any legacy format.
+
+- __HAVE_ZLIB__ : `zstd` can compress and decompress files in `.gz` format.
+  This is ordered through command `--format=gzip`.
+  Alternatively, symlinks named `gzip` or `gunzip` will mimic intended behavior.
+  `.gz` support is automatically enabled when `zlib` library is detected at build time.
+  It's possible to disable `.gz` support, by setting `HAVE_ZLIB=0`.
+  Example : `make zstd HAVE_ZLIB=0`
+  It's also possible to force compilation with zlib support, using `HAVE_ZLIB=1`.
+  In which case, linking stage will fail if `zlib` library cannot be found.
+  This is useful to prevent silent feature disabling.
+
+- __HAVE_LZMA__ : `zstd` can compress and decompress files in `.xz` and `.lzma` formats.
+  This is ordered through commands `--format=xz` and `--format=lzma` respectively.
+  Alternatively, symlinks named `xz`, `unxz`, `lzma`, or `unlzma` will mimic intended behavior.
+  `.xz` and `.lzma` support is automatically enabled when `lzma` library is detected at build time.
+  It's possible to disable `.xz` and `.lzma` support, by setting `HAVE_LZMA=0`.
+  Example : `make zstd HAVE_LZMA=0`
+  It's also possible to force compilation with lzma support, using `HAVE_LZMA=1`.
+  In which case, linking stage will fail if `lzma` library cannot be found.
+  This is useful to prevent silent feature disabling.
+
+- __HAVE_LZ4__ : `zstd` can compress and decompress files in `.lz4` formats.
+  This is ordered through commands `--format=lz4`.
+  Alternatively, symlinks named `lz4`, or `unlz4` will mimic intended behavior.
+  `.lz4` support is automatically enabled when `lz4` library is detected at build time.
+  It's possible to disable `.lz4` support, by setting `HAVE_LZ4=0` .
+  Example : `make zstd HAVE_LZ4=0`
+  It's also possible to force compilation with lz4 support, using `HAVE_LZ4=1`.
+  In which case, linking stage will fail if `lz4` library cannot be found.
+  This is useful to prevent silent feature disabling.
+
+- __ZSTD_NOBENCH__ : `zstd` cli will be compiled without its integrated benchmark module.
+  This can be useful to produce smaller binaries.
+  In this case, the corresponding unit can also be excluded from compilation target.
+
+- __ZSTD_NODICT__ : `zstd` cli will be compiled without support for the integrated dictionary builder.
+  This can be useful to produce smaller binaries.
+  In this case, the corresponding unit can also be excluded from compilation target.
+
+- __ZSTD_NOCOMPRESS__ : `zstd` cli will be compiled without support for compression.
+  The resulting binary will only be able to decompress files.
+  This can be useful to produce smaller binaries.
+  A corresponding `Makefile` target using this ability is `zstd-decompress`.
+
+- __ZSTD_NODECOMPRESS__ : `zstd` cli will be compiled without support for decompression.
+  The resulting binary will only be able to compress files.
+  This can be useful to produce smaller binaries.
+  A corresponding `Makefile` target using this ability is `zstd-compress`.
+
+- __BACKTRACE__ : `zstd` can display a stack backtrace when execution
+  generates a runtime exception. By default, this feature may be
+  degraded/disabled on some platforms unless additional compiler directives are
+  applied. When triaging a runtime issue, enabling this feature can provide
+  more context to determine the location of the fault.
+  Example : `make zstd BACKTRACE=1`
+
+
+### Aggregation of parameters
+CLI supports aggregation of parameters i.e. `-b1`, `-e18`, and `-i1` can be joined into `-b1e18i1`.
+
+
+### Symlink shortcuts
+It's possible to invoke `zstd` through a symlink.
+When the name of the symlink has a specific value, it triggers an associated behavior.
+- `zstdmt` : compress using all cores available on local system.
+- `zcat` : will decompress and output target file using any of the supported formats. `gzcat` and `zstdcat` are also equivalent.
+- `gzip` : if zlib support is enabled, will mimic `gzip` by compressing file using `.gz` format, removing source file by default (use `--keep` to preserve). If zlib is not supported, triggers an error.
+- `xz` : if lzma support is enabled, will mimic `xz` by compressing file using `.xz` format, removing source file by default (use `--keep` to preserve). If xz is not supported, triggers an error.
+- `lzma` : if lzma support is enabled, will mimic `lzma` by compressing file using `.lzma` format, removing source file by default (use `--keep` to preserve). If lzma is not supported, triggers an error.
+- `lz4` : if lz4 support is enabled, will mimic `lz4` by compressing file using `.lz4` format. If lz4 is not supported, triggers an error.
+- `unzstd` and `unlz4` will decompress any of the supported format.
+- `ungz`, `unxz` and `unlzma` will do the same, and will also remove source file by default (use `--keep` to preserve).
+
+
+### Dictionary builder in Command Line Interface
+Zstd offers a training mode, which can be used to tune the algorithm for a selected
+type of data, by providing it with a few samples. The result of the training is stored
+in a file selected with the `-o` option (default name is `dictionary`),
+which can be loaded before compression and decompression.
+
+Using a dictionary, the compression ratio achievable on small data improves dramatically.
+These compression gains are achieved while simultaneously providing faster compression and decompression speeds.
+Dictionary work if there is some correlation in a family of small data (there is no universal dictionary).
+Hence, deploying one dictionary per type of data will provide the greater benefits.
+Dictionary gains are mostly effective in the first few KB. Then, the compression algorithm
+will rely more and more on previously decoded content to compress the rest of the file.
+
+Usage of the dictionary builder and created dictionaries with CLI:
+
+1. Create the dictionary : `zstd --train PathToTrainingSet/* -o dictionaryName`
+2. Compress with the dictionary: `zstd FILE -D dictionaryName`
+3. Decompress with the dictionary: `zstd --decompress FILE.zst -D dictionaryName`
+
+
+### Benchmark in Command Line Interface
+CLI includes in-memory compression benchmark module for zstd.
+The benchmark is conducted using given filenames. The files are read into memory and joined together.
+It makes benchmark more precise as it eliminates I/O overhead.
+Multiple filenames can be supplied, as multiple parameters, with wildcards,
+or names of directories can be used as parameters with `-r` option.
+
+The benchmark measures ratio, compressed size, compression and decompression speed.
+One can select compression levels starting from `-b` and ending with `-e`.
+The `-i` parameter selects minimal time used for each of tested levels.
+
+
+### Usage of Command Line Interface
+The full list of options can be obtained with `-h` or `-H` parameter:
+```
+Usage :
+      zstd [args] [FILE(s)] [-o file]
+
+FILE    : a filename
+          with no FILE, or when FILE is - , read standard input
+Arguments :
+ -#     : # compression level (1-19, default: 3)
+ -d     : decompression
+ -D file: use `file` as Dictionary
+ -o file: result stored into `file` (only if 1 input file)
+ -f     : overwrite output without prompting and (de)compress links
+--rm    : remove source file(s) after successful de/compression
+ -k     : preserve source file(s) (default)
+ -h/-H  : display help/long help and exit
+
+Advanced arguments :
+ -V     : display Version number and exit
+ -v     : verbose mode; specify multiple times to increase verbosity
+ -q     : suppress warnings; specify twice to suppress errors too
+ -c     : force write to standard output, even if it is the console
+ -l     : print information about zstd compressed files
+--exclude-compressed:  only compress files that are not previously compressed
+--ultra : enable levels beyond 19, up to 22 (requires more memory)
+--long[=#]: enable long distance matching with given window log (default: 27)
+--fast[=#]: switch to very fast compression levels (default: 1)
+--adapt : dynamically adapt compression level to I/O conditions
+--stream-size=# : optimize compression parameters for streaming input of given number of bytes
+--size-hint=# optimize compression parameters for streaming input of approximately this size
+--target-compressed-block-size=# : make compressed block near targeted size
+ -T#    : spawns # compression threads (default: 1, 0==# cores)
+ -B#    : select size of each job (default: 0==automatic)
+--rsyncable : compress using a rsync-friendly method (-B sets block size)
+--no-dictID : don't write dictID into header (dictionary compression)
+--[no-]check : integrity check (default: enabled)
+--[no-]compress-literals : force (un)compressed literals
+ -r     : operate recursively on directories
+--output-dir-flat[=directory]: all resulting files stored into `directory`.
+--format=zstd : compress files to the .zst format (default)
+--format=gzip : compress files to the .gz format
+--test  : test compressed file integrity
+--[no-]sparse : sparse mode (default: disabled)
+ -M#    : Set a memory usage limit for decompression
+--no-progress : do not display the progress bar
+--      : All arguments after "--" are treated as files
+
+Dictionary builder :
+--train ## : create a dictionary from a training set of files
+--train-cover[=k=#,d=#,steps=#,split=#,shrink[=#]] : use the cover algorithm with optional args
+--train-fastcover[=k=#,d=#,f=#,steps=#,split=#,accel=#,shrink[=#]] : use the fast cover algorithm with optional args
+--train-legacy[=s=#] : use the legacy algorithm with selectivity (default: 9)
+ -o file : `file` is dictionary name (default: dictionary)
+--maxdict=# : limit dictionary to specified size (default: 112640)
+--dictID=# : force dictionary ID to specified value (default: random)
+
+Benchmark arguments :
+ -b#    : benchmark file(s), using # compression level (default: 3)
+ -e#    : test all compression levels from -bX to # (default: 1)
+ -i#    : minimum evaluation time in seconds (default: 3s)
+ -B#    : cut file into independent blocks of size # (default: no block)
+--priority=rt : set process priority to real-time
+```
+
+### Passing parameters through Environment Variables
+`ZSTD_CLEVEL` can be used to modify the default compression level of `zstd`
+(usually set to `3`) to another value between 1 and 19 (the "normal" range).
+This can be useful when `zstd` CLI is invoked in a way that doesn't allow passing arguments.
+One such scenario is `tar --zstd`.
+As `ZSTD_CLEVEL` only replaces the default compression level,
+it can then be overridden by corresponding command line arguments.
+
+There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner.
+Using environment variables for this purpose has security implications.
+Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL`.
+
+### Long distance matching mode
+The long distance matching mode, enabled with `--long`, is designed to improve
+the compression ratio for files with long matches at a large distance (up to the
+maximum window size, `128 MiB`) while still maintaining compression speed.
+
+Enabling this mode sets the window size to `128 MiB` and thus increases the memory
+usage for both the compressor and decompressor. Performance in terms of speed is
+dependent on long matches being found. Compression speed may degrade if few long
+matches are found. Decompression speed usually improves when there are many long
+distance matches.
+
+Below are graphs comparing the compression speed, compression ratio, and
+decompression speed with and without long distance matching on an ideal use
+case: a tar of four versions of clang (versions `3.4.1`, `3.4.2`, `3.5.0`,
+`3.5.1`) with a total size of `244889600 B`. This is an ideal use case as there
+are many long distance matches within the maximum window size of `128 MiB` (each
+version is less than `128 MiB`).
+
+Compression Speed vs Ratio | Decompression Speed
+---------------------------|---------------------
+![Compression Speed vs Ratio](https://raw.githubusercontent.com/facebook/zstd/v1.3.3/doc/images/ldmCspeed.png "Compression Speed vs Ratio") | ![Decompression Speed](https://raw.githubusercontent.com/facebook/zstd/v1.3.3/doc/images/ldmDspeed.png "Decompression Speed")
+
+| Method | Compression ratio | Compression speed | Decompression speed  |
+|:-------|------------------:|-------------------------:|---------------------------:|
+| `zstd -1`  | `5.065`    | `284.8 MB/s`  | `759.3 MB/s`  |
+| `zstd -5`  | `5.826`    | `124.9 MB/s`  | `674.0 MB/s`  |
+| `zstd -10` | `6.504`    | `29.5 MB/s`   | `771.3 MB/s`  |
+| `zstd -1 --long` | `17.426` | `220.6 MB/s` | `1638.4 MB/s` |
+| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s` |
+| `zstd -10 --long`| `21.949` |  `75.6 MB/s` | `1632.6 MB/s` |
+
+On this file, the compression ratio improves significantly with minimal impact
+on compression speed, and the decompression speed doubles.
+
+On the other extreme, compressing a file with few long distance matches (such as
+the [Silesia compression corpus]) will likely lead to a deterioration in
+compression speed (for lower levels) with minimal change in compression ratio.
+
+The below table illustrates this on the [Silesia compression corpus].
+
+[Silesia compression corpus]: http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia
+
+| Method | Compression ratio | Compression speed | Decompression speed  |
+|:-------|------------------:|------------------:|---------------------:|
+| `zstd -1`        | `2.878` | `231.7 MB/s`      | `594.4 MB/s`   |
+| `zstd -1 --long` | `2.929` | `106.5 MB/s`      | `517.9 MB/s`   |
+| `zstd -5`        | `3.274` | `77.1 MB/s`       | `464.2 MB/s`   |
+| `zstd -5 --long` | `3.319` | `51.7 MB/s`       | `371.9 MB/s`   |
+| `zstd -10`       | `3.523` | `16.4 MB/s`       | `489.2 MB/s`   |
+| `zstd -10 --long`| `3.566` | `16.2 MB/s`       | `415.7 MB/s`   |
+
+
+### zstdgrep
+
+`zstdgrep` is a utility which makes it possible to `grep` directly a `.zst` compressed file.
+It's used the same way as normal `grep`, for example :
+`zstdgrep pattern file.zst`
+
+`zstdgrep` is _not_ compatible with dictionary compression.
+
+To search into a file compressed with a dictionary,
+it's necessary to decompress it using `zstd` or `zstdcat`,
+and then pipe the result to `grep`. For example  :
+`zstdcat -D dictionary -qc -- file.zst | grep pattern`