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dll/example | ||
.gitignore | ||
liblz4-dll.rc.in | ||
liblz4.pc.in | ||
LICENSE | ||
lz4.c | ||
lz4.h | ||
lz4frame_static.h | ||
lz4frame.c | ||
lz4frame.h | ||
lz4hc.c | ||
lz4hc.h | ||
Makefile | ||
README.md | ||
xxhash.c | ||
xxhash.h |
LZ4 - Library Files
The /lib
directory contains many files, but depending on project's objectives,
not all of them are necessary.
Minimal LZ4 build
The minimum required is lz4.c
and lz4.h
,
which provides the fast compression and decompression algorithms.
They generate and decode data using the LZ4 block format.
High Compression variant
For more compression ratio at the cost of compression speed,
the High Compression variant called lz4hc is available.
Add files lz4hc.c
and lz4hc.h
.
This variant also compresses data using the LZ4 block format,
and depends on regular lib/lz4.*
source files.
Frame support, for interoperability
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 *.c
and *.h
files present in /lib
.
Advanced / Experimental API
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 LZ4_PUBLISH_STATIC_FUNCTIONS
and LZ4F_PUBLISH_STATIC_FUNCTIONS
.
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 x86, x64 and aarch64 cpus, and is automatically enabled for them. It's also possible to enable or disable it manually, by passingLZ4_FAST_DEC_LOOP=1
or0
to the preprocessor. For example, withgcc
:-DLZ4_FAST_DEC_LOOP=1
, and withmake
: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-Wno-deprecated-declarations
ongcc
, or_CRT_SECURE_NO_WARNINGS
for Visual Studio. Another project-specific method is to defineLZ4_DISABLE_DEPRECATE_WARNINGS
before including the LZ4 header files. -
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.
Amalgamation
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 lz4_all.c
.
All *.h
files present in /lib
remain necessary to compile lz4_all.c
.
Windows : using MinGW+MSYS to create DLL
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 lz4.h
, lz4hc.h
, 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 dll\liblz4.dll
.
Miscellaneous
Other files present in the directory are not source code. They are :
LICENSE
: contains the BSD license textMakefile
:make
script to compile and install lz4 library (static and dynamic)liblz4.pc.in
: forpkg-config
(used inmake install
)README.md
: this file
License
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.