Added snappy-1.1.3 compression library

external/snappy-1.1.3/README

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+Snappy, a fast compressor/decompressor.
+
+
+Introduction
+============
+
+Snappy is a compression/decompression library. It does not aim for maximum
+compression, or compatibility with any other compression library; instead,
+it aims for very high speeds and reasonable compression. For instance,
+compared to the fastest mode of zlib, Snappy is an order of magnitude faster
+for most inputs, but the resulting compressed files are anywhere from 20% to
+100% bigger. (For more information, see "Performance", below.)
+
+Snappy has the following properties:
+
+ * Fast: Compression speeds at 250 MB/sec and beyond, with no assembler code.
+   See "Performance" below.
+ * Stable: Over the last few years, Snappy has compressed and decompressed
+   petabytes of data in Google's production environment. The Snappy bitstream
+   format is stable and will not change between versions.
+ * Robust: The Snappy decompressor is designed not to crash in the face of
+   corrupted or malicious input.
+ * Free and open source software: Snappy is licensed under a BSD-type license.
+   For more information, see the included COPYING file.
+
+Snappy has previously been called "Zippy" in some Google presentations
+and the like.
+
+
+Performance
+===========
+ 
+Snappy is intended to be fast. On a single core of a Core i7 processor
+in 64-bit mode, it compresses at about 250 MB/sec or more and decompresses at
+about 500 MB/sec or more. (These numbers are for the slowest inputs in our
+benchmark suite; others are much faster.) In our tests, Snappy usually
+is faster than algorithms in the same class (e.g. LZO, LZF, FastLZ, QuickLZ,
+etc.) while achieving comparable compression ratios.
+
+Typical compression ratios (based on the benchmark suite) are about 1.5-1.7x
+for plain text, about 2-4x for HTML, and of course 1.0x for JPEGs, PNGs and
+other already-compressed data. Similar numbers for zlib in its fastest mode
+are 2.6-2.8x, 3-7x and 1.0x, respectively. More sophisticated algorithms are
+capable of achieving yet higher compression rates, although usually at the
+expense of speed. Of course, compression ratio will vary significantly with
+the input.
+
+Although Snappy should be fairly portable, it is primarily optimized
+for 64-bit x86-compatible processors, and may run slower in other environments.
+In particular:
+
+ - Snappy uses 64-bit operations in several places to process more data at
+   once than would otherwise be possible.
+ - Snappy assumes unaligned 32- and 64-bit loads and stores are cheap.
+   On some platforms, these must be emulated with single-byte loads 
+   and stores, which is much slower.
+ - Snappy assumes little-endian throughout, and needs to byte-swap data in
+   several places if running on a big-endian platform.
+
+Experience has shown that even heavily tuned code can be improved.
+Performance optimizations, whether for 64-bit x86 or other platforms,
+are of course most welcome; see "Contact", below.
+
+
+Usage
+=====
+
+Note that Snappy, both the implementation and the main interface,
+is written in C++. However, several third-party bindings to other languages
+are available; see the Google Code page at http://code.google.com/p/snappy/
+for more information. Also, if you want to use Snappy from C code, you can
+use the included C bindings in snappy-c.h.
+
+To use Snappy from your own C++ program, include the file "snappy.h" from
+your calling file, and link against the compiled library.
+
+There are many ways to call Snappy, but the simplest possible is
+
+  snappy::Compress(input.data(), input.size(), &output);
+
+and similarly
+
+  snappy::Uncompress(input.data(), input.size(), &output);
+
+where "input" and "output" are both instances of std::string.
+
+There are other interfaces that are more flexible in various ways, including
+support for custom (non-array) input sources. See the header file for more
+information.
+
+
+Tests and benchmarks
+====================
+
+When you compile Snappy, snappy_unittest is compiled in addition to the
+library itself. You do not need it to use the compressor from your own library,
+but it contains several useful components for Snappy development.
+
+First of all, it contains unit tests, verifying correctness on your machine in
+various scenarios. If you want to change or optimize Snappy, please run the
+tests to verify you have not broken anything. Note that if you have the
+Google Test library installed, unit test behavior (especially failures) will be
+significantly more user-friendly. You can find Google Test at
+
+  http://code.google.com/p/googletest/
+
+You probably also want the gflags library for handling of command-line flags;
+you can find it at
+
+  http://code.google.com/p/google-gflags/
+
+In addition to the unit tests, snappy contains microbenchmarks used to
+tune compression and decompression performance. These are automatically run
+before the unit tests, but you can disable them using the flag
+--run_microbenchmarks=false if you have gflags installed (otherwise you will
+need to edit the source).
+
+Finally, snappy can benchmark Snappy against a few other compression libraries
+(zlib, LZO, LZF, FastLZ and QuickLZ), if they were detected at configure time.
+To benchmark using a given file, give the compression algorithm you want to test
+Snappy against (e.g. --zlib) and then a list of one or more file names on the
+command line. The testdata/ directory contains the files used by the
+microbenchmark, which should provide a reasonably balanced starting point for
+benchmarking. (Note that baddata[1-3].snappy are not intended as benchmarks; they
+are used to verify correctness in the presence of corrupted data in the unit
+test.)
+
+
+Contact
+=======
+
+Snappy is distributed through Google Code. For the latest version, a bug tracker,
+and other information, see
+
+  http://code.google.com/p/snappy/