/lib directory contains many files, but depending on project's objectives, not all of them are necessary.
The minimum required is
lz4.h, which provides the fast compression and decompression algorithms. They generate and decode data using the LZ4 block format.
For more compression ratio at the cost of compression speed, the High Compression variant called lz4hc is available. Add files
lz4hc.h. This variant also compresses data using the LZ4 block format, and depends on regular
lib/lz4.* source files.
In order to produce compressed data compatible with
lz4 command line utility, it‘s necessary to use the official interoperable frame format. This format is generated and decoded automatically by the lz4frame library. Its public API is described in
lib/lz4frame.h. In order to work properly, lz4frame needs all other modules present in
/lib, including, lz4 and lz4hc, and also xxhash. So it’s necessary to include all
*.h files present in
Definitions which are not guaranteed to remain stable in future versions, are protected behind macros, such as
LZ4_STATIC_LINKING_ONLY. As the name strongly implies, these definitions should only be invoked in the context of static linking only. Otherwise, dependent application may fail on API or ABI break in the future. The associated symbols are also not exposed by the dynamic library by default. Should they be nonetheless needed, it's possible to force their publication by using build macros
The following build macro can be selected to adjust source code behavior at compilation time :
LZ4_FAST_DEC_LOOP : this triggers a speed optimized decompression loop, more powerful on modern cpus. This loop works great on
aarch64 cpus, and is automatically enabled for them. It's also possible to enable or disable it manually, by passing
0 to the preprocessor. For example, with
-DLZ4_FAST_DEC_LOOP=1, and with
CPPFLAGS+=-DLZ4_FAST_DEC_LOOP=1 make lz4.
LZ4_DISTANCE_MAX : control the maximum offset that the compressor will allow. Set to 65535 by default, which is the maximum value supported by lz4 format. Reducing maximum distance will reduce opportunities for LZ4 to find matches, hence will produce a worse compression ratio. However, a smaller max distance can allow compatibility with specific decoders using limited memory budget. This build macro only influences the compressed output of the compressor.
LZ4_DISABLE_DEPRECATE_WARNINGS : invoking a deprecated function will make the compiler generate a warning. This is meant to invite users to update their source code. Should this be a problem, it's generally possible to make the compiler ignore these warnings, for example with
_CRT_SECURE_NO_WARNINGS for Visual Studio. This build macro offers another project-specific method by defining
LZ4_DISABLE_DEPRECATE_WARNINGS before including the LZ4 header files.
LZ4_USER_MEMORY_FUNCTIONS : replace calls to 's
free by user-defined functions, which must be called
LZ4_free(). User functions must be available at link time.
LZ4_FORCE_SW_BITCOUNT : by default, the compression algorithm tries to determine lengths by using bitcount instructions, generally implemented as fast single instructions in many cpus. In case the target cpus doesn‘t support it, or compiler intrinsic doesn’t work, or feature bad performance, it‘s possible to use an optimized software path instead. This is achieved by setting this build macros . In most cases, it’s not expected to be necessary, but it can be legitimately considered for less common platforms.
LZ4_ALIGN_TEST : alignment test ensures that the memory area passed as argument to become a compression state is suitably aligned. This test can be disabled if it proves flaky, by setting this value to 0.
lz4 source code can be amalgamated into a single file. One can combine all source code into
lz4_all.c by using following command:
cat lz4.c lz4hc.c lz4frame.c > lz4_all.c
cat file order is important) then compile
*.h files present in
/lib remain necessary to compile
DLL can be created using MinGW+MSYS with the
make liblz4 command. This command creates
dll\liblz4.dll and the import library
dll\liblz4.lib. To override the
dlltool command when cross-compiling on Linux, just set the
DLLTOOL variable. Example of cross compilation on Linux with mingw-w64 64 bits:
make BUILD_STATIC=no CC=x86_64-w64-mingw32-gcc DLLTOOL=x86_64-w64-mingw32-dlltool OS=Windows_NT
The import library is only required with Visual C++. The header files
lz4frame.h and the dynamic library
dll\liblz4.dll are required to compile a project using gcc/MinGW. The dynamic library has to be added to linking options. It means that if a project that uses LZ4 consists of a single
test-dll.c file it should be linked with
dll\liblz4.dll. For example:
$(CC) $(CFLAGS) -Iinclude/ test-dll.c -o test-dll dll\liblz4.dll
The compiled executable will require LZ4 DLL which is available at
Other files present in the directory are not source code. They are :
LICENSE: contains the BSD license text
makescript to compile and install lz4 library (static and dynamic)
README.md: this file
All source material within lib directory are BSD 2-Clause licensed. See LICENSE for details. The license is also reminded at the top of each source file.