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The `/lib` directory contains many files, but depending on project's objectives,
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not all of them are necessary.
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not all of them are required.
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Limited systems may want to reduce the nb of source files to include
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as a way to reduce binary size and dependencies.
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Capabilities are added at the "level" granularity, detailed below.
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#### Level 1 : Minimal LZ4 build
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The minimum required is **`lz4.c`** and **`lz4.h`**,
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which provides the fast compression and decompression algorithms.
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They generate and decode data using the [LZ4 block format].
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#### High Compression variant
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#### Level 2 : High Compression variant
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For more compression ratio at the cost of compression speed,
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the High Compression variant called **lz4hc** is available.
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and depends on regular `lib/lz4.*` source files.
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#### Frame support, for interoperability
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#### Level 3 : Frame support, for interoperability
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In order to produce compressed data compatible with `lz4` command line utility,
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it's necessary to use the [official interoperable frame format].
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Its public API is described in `lib/lz4frame.h`.
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In order to work properly, lz4frame needs all other modules present in `/lib`,
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including, lz4 and lz4hc, and also **xxhash**.
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So it's necessary to include all `*.c` and `*.h` files present in `/lib`.
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So it's necessary to also include `xxhash.c` and `xxhash.h`.
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#### Level 4 : File compression operations
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As a helper around file operations,
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the library has been recently extended with `lz4file.c` and `lz4file.h`
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(still considered experimental at the time of this writing).
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These helpers allow opening, reading, writing, and closing files
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using transparent LZ4 compression / decompression.
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As a consequence, using `lz4file` adds a dependency on `<stdio.h>`.
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`lz4file` relies on `lz4frame` in order to produce compressed data
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conformant to the [LZ4 Frame format] specification.
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Consequently, to enable this capability,
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it's necessary to include all `*.c` and `*.h` files from `lib/` directory.
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#### Advanced / Experimental API
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Definitions which are not guaranteed to remain stable in future versions,
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are protected behind macros, such as `LZ4_STATIC_LINKING_ONLY`.
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As the name strongly implies, these definitions should only be invoked
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As the name suggests, these definitions should only be invoked
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in the context of static linking ***only***.
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Otherwise, dependent application may fail on API or ABI break in the future.
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The associated symbols are also not exposed by the dynamic library by default.
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Set to 65535 by default, which is the maximum value supported by lz4 format.
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Reducing maximum distance will reduce opportunities for LZ4 to find matches,
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hence will produce a worse compression ratio.
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However, a smaller max distance can allow compatibility with specific decoders using limited memory budget.
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Setting a smaller max distance could allow compatibility with specific decoders with limited memory budget.
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This build macro only influences the compressed output of the compressor.
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- `LZ4_DISABLE_DEPRECATE_WARNINGS` : invoking a deprecated function will make the compiler generate a warning.
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This build macro offers another project-specific method
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by defining `LZ4_DISABLE_DEPRECATE_WARNINGS` before including the LZ4 header files.
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- `LZ4_USER_MEMORY_FUNCTIONS` : replace calls to <stdlib>'s `malloc`, `calloc` and `free`
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by user-defined functions, which must be called `LZ4_malloc()`, `LZ4_calloc()` and `LZ4_free()`.
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User functions must be available at link time.
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- `LZ4_FORCE_SW_BITCOUNT` : by default, the compression algorithm tries to determine lengths
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by using bitcount instructions, generally implemented as fast single instructions in many cpus.
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In case the target cpus doesn't support it, or compiler intrinsic doesn't work, or feature bad performance,
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it's possible to use an optimized software path instead.
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This is achieved by setting this build macros .
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This is achieved by setting this build macros.
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In most cases, it's not expected to be necessary,
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but it can be legitimately considered for less common platforms.
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passed as argument to become a compression state is suitably aligned.
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This test can be disabled if it proves flaky, by setting this value to 0.
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- `LZ4_USER_MEMORY_FUNCTIONS` : replace calls to `<stdlib,h>`'s `malloc()`, `calloc()` and `free()`
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by user-defined functions, which must be named `LZ4_malloc()`, `LZ4_calloc()` and `LZ4_free()`.
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User functions must be available at link time.
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- `LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION` :
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Remove support of dynamic memory allocation.
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For more details, see description of this macro in `lib/lz4.c`.
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- `LZ4_FREESTANDING` : by setting this build macro to 1,
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LZ4/HC removes dependencies on the C standard library,
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including allocation functions and `memmove()`, `memcpy()`, and `memset()`.
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This build macro is designed to help use LZ4/HC in restricted environments
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(embedded, bootloader, etc).
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For more details, see description of this macro in `lib/lz4.h`.
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DLL can be created using MinGW+MSYS with the `make liblz4` command.
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This command creates `dll\liblz4.dll` and the import library `dll\liblz4.lib`.
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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:
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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:
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make BUILD_STATIC=no CC=x86_64-w64-mingw32-gcc DLLTOOL=x86_64-w64-mingw32-dlltool OS=Windows_NT
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lib/README.md
