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[pcsx_rearmed.git] / deps / libchdr / deps / zstd-1.5.5 / contrib / pzstd / README.md

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+# Parallel Zstandard (PZstandard)
+
+Parallel Zstandard is a Pigz-like tool for Zstandard.
+It provides Zstandard format compatible compression and decompression that is able to utilize multiple cores.
+It breaks the input up into equal sized chunks and compresses each chunk independently into a Zstandard frame.
+It then concatenates the frames together to produce the final compressed output.
+Pzstandard will write a 12 byte header for each frame that is a skippable frame in the Zstandard format, which tells PZstandard the size of the next compressed frame.
+PZstandard supports parallel decompression of files compressed with PZstandard.
+When decompressing files compressed with Zstandard, PZstandard does IO in one thread, and decompression in another.
+
+## Usage
+
+PZstandard supports the same command line interface as Zstandard, but also provides the `-p` option to specify the number of threads.
+Dictionary mode is not currently supported.
+
+Basic usage
+
+    pzstd input-file -o output-file -p num-threads -#          # Compression
+    pzstd -d input-file -o output-file -p num-threads          # Decompression
+
+PZstandard also supports piping and fifo pipes
+
+    cat input-file | pzstd -p num-threads -# -c > /dev/null
+
+For more options
+
+    pzstd --help
+
+PZstandard tries to pick a smart default number of threads if not specified (displayed in `pzstd --help`).
+If this number is not suitable, during compilation you can define `PZSTD_NUM_THREADS` to the number of threads you prefer.
+
+## Benchmarks
+
+As a reference, PZstandard and Pigz were compared on an Intel Core i7 @ 3.1 GHz, each using 4 threads, with the [Silesia compression corpus](https://sun.aei.polsl.pl//~sdeor/index.php?page=silesia).
+
+Compression Speed vs Ratio with 4 Threads | Decompression Speed with 4 Threads
+------------------------------------------|-----------------------------------
+![Compression Speed vs Ratio](images/Cspeed.png "Compression Speed vs Ratio") | ![Decompression Speed](images/Dspeed.png "Decompression Speed")
+
+The test procedure was to run each of the following commands 2 times for each compression level, and take the minimum time.
+
+    time pzstd -# -p 4    -c silesia.tar     > silesia.tar.zst
+    time pzstd -d -p 4    -c silesia.tar.zst > /dev/null
+
+    time pigz  -# -p 4 -k -c silesia.tar     > silesia.tar.gz
+    time pigz  -d -p 4 -k -c silesia.tar.gz  > /dev/null
+
+PZstandard was tested using compression levels 1-19, and Pigz was tested using compression levels 1-9.
+Pigz cannot do parallel decompression, it simply does each of reading, decompression, and writing on separate threads.
+
+## Tests
+
+Tests require that you have [gtest](https://github.com/google/googletest) installed.
+Set `GTEST_INC` and `GTEST_LIB` in `Makefile` to specify the location of the gtest headers and libraries.
+Alternatively, run `make googletest`, which will clone googletest and build it.
+Run `make tests && make check` to run tests.