zstd/lib

Zstandard library files

The lib directory is split into several sub-directories, in order to make it easier to select or exclude features.

Building

Makefile script is provided, supporting all standard Makefile conventions, including commands variables, staged install, directory variables and standard targets.

• make : generates both static and dynamic libraries
• make install : install libraries in default system directories

libzstd default scope includes compression, decompression, dictionary building, and decoding support for legacy formats >= v0.5.0.

API

Zstandard's stable API is exposed within lib/zstd.h.

Advanced API

Optional advanced features are exposed via :

• lib/common/zstd_errors.h : translates size_t function results into an ZSTD_ErrorCode, for accurate error handling.
• ZSTD_STATIC_LINKING_ONLY : if this macro is defined before including zstd.h, it unlocks access to advanced experimental API, exposed in second part of zstd.h. These APIs are not "stable", their definition may change in the future. As a consequence, it shall never be used with dynamic library ! Only static linking is allowed.

Modular build

It's possible to compile only a limited set of features.

• Directory lib/common is always required, for all variants.

• Compression source code lies in lib/compress

• Decompression source code lies in lib/decompress

• It's possible to include only compress or only decompress, they don't depend on each other.

• lib/dictBuilder : makes it possible to generate dictionaries from a set of samples. The API is exposed in lib/dictBuilder/zdict.h. This module depends on both lib/common and lib/compress .

• lib/legacy : source code to decompress legacy zstd formats, starting from v0.1.0. This module depends on lib/common and lib/decompress. To enable this feature, define ZSTD_LEGACY_SUPPORT during compilation. Specifying a number limits versions supported to that version onward. For example, ZSTD_LEGACY_SUPPORT=2 means : "support legacy formats >= v0.2.0". ZSTD_LEGACY_SUPPORT=3 means : "support legacy formats >= v0.3.0", and so on. Currently, the default library setting is ZST_LEGACY_SUPPORT=5. It can be changed at build by any other value. Note that any number >= 8 translates into "do not support legacy formats", since all versions of zstd >= v0.8 are compatible with v1+ specification. ZSTD_LEGACY_SUPPORT=0 also means "do not support legacy formats". Once enabled, this capability is transparently triggered within decompression functions. It's also possible to invoke directly legacy API, as exposed in lib/legacy/zstd_legacy.h. Each version also provides an additional dedicated set of advanced API. For example, advanced API for version v0.4 is exposed in lib/legacy/zstd_v04.h . Note : lib/legacy only supports decoding legacy formats.

• Similarly, you can define ZSTD_LIB_COMPRESSION, ZSTD_LIB_DECOMPRESSION, ZSTD_LIB_DICTBUILDER, and ZSTD_LIB_DEPRECATED as 0 to forgo compilation of the corresponding features. This will also disable compilation of all dependencies (eg. ZSTD_LIB_COMPRESSION=0 will also disable dictBuilder).

• There are some additional macros that can be used to minify the decoder.

  Zstandard often has more than one implementation of a piece of functionality, where each implementation optimizes for different scenarios. For example, the Huffman decoder has complementary implementations that decode the stream one symbol at a time or two symbols at a time. Zstd normally includes both (and dispatches between them at runtime), but by defining HUF_FORCE_DECOMPRESS_X1 or HUF_FORCE_DECOMPRESS_X2, you can force the use of one or the other, avoiding compilation of the other. Similarly, ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT and ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG force the compilation and use of only one or the other of two decompression implementations. The smallest binary is achieved by using HUF_FORCE_DECOMPRESS_X1 and ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT.

  For squeezing the last ounce of size out, you can also define ZSTD_NO_INLINE, which disables inlining, and ZSTD_STRIP_ERROR_STRINGS, which removes the error messages that are otherwise returned by ZSTD_getErrorName.

Multithreading support

Multithreading is disabled by default when building with make. Enabling multithreading requires 2 conditions :

• set macro ZSTD_MULTITHREAD
• on POSIX systems : compile with pthread (-pthread compilation flag for gcc)

Both conditions are automatically triggered by invoking make lib-mt target. Note that, when linking a POSIX program with a multithreaded version of libzstd, it's necessary to trigger -pthread flag during link stage.

Multithreading capabilities are exposed via advanced API ZSTD_compress_generic() defined in lib/zstd.h. This API is still considered experimental, but is expected to become "stable" at some point in the future.

Windows : using MinGW+MSYS to create DLL

DLL can be created using MinGW+MSYS with the make libzstd command. This command creates dll\libzstd.dll and the import library dll\libzstd.lib. The import library is only required with Visual C++. The header file zstd.h and the dynamic library dll\libzstd.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 ZSTD consists of a single test-dll.c file it should be linked with dll\libzstd.dll. For example:

    gcc $(CFLAGS) -Iinclude/ test-dll.c -o test-dll dll\libzstd.dll

The compiled executable will require ZSTD DLL which is available at dll\libzstd.dll.

Deprecated API

Obsolete API on their way out are stored in directory lib/deprecated. At this stage, it contains older streaming prototypes, in lib/deprecated/zbuff.h. These prototypes will be removed in some future version. Consider migrating code towards supported streaming API exposed in zstd.h.

Miscellaneous

The other files are not source code. There are :

• LICENSE : contains the BSD license text
• Makefile : make script to build and install zstd library (static and dynamic)
• BUCK : support for buck build system (https://buckbuild.com/)
• libzstd.pc.in : for pkg-config (used in make install)
• README.md : this file