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 [Makefile conventions](https://www.gnu.org/prep/standards/html_node/Makefile-Conventions.html#Makefile-Conventions), including commands variables, staged install, directory variables and standard targets. - `make` : generates both static and dynamic libraries - `make install` : install libraries and headers in target system directories `libzstd` default scope is pretty large, including compression, decompression, dictionary builder, and support for decoding legacy formats >= v0.5.0. The scope can be reduced on demand (see paragraph _modular build_). #### Multithreading support Multithreading is disabled by default when building with `make`. Enabling multithreading requires 2 conditions : - set build macro `ZSTD_MULTITHREAD` (`-DZSTD_MULTITHREAD` for `gcc`) - for POSIX systems : compile with pthread (`-pthread` compilation flag for `gcc`) Both conditions are automatically applied when invoking `make lib-mt` target. When linking a POSIX program with a multithreaded version of `libzstd`, note that it's necessary to request the `-pthread` flag during link stage. Multithreading capabilities are exposed via the [advanced API defined in `lib/zstd.h`](https://github.com/facebook/zstd/blob/v1.3.8/lib/zstd.h#L592). #### API Zstandard's stable API is exposed within [lib/zstd.h](zstd.h). #### Advanced API Optional advanced features are exposed via : - `lib/common/zstd_errors.h` : translates `size_t` function results into a `ZSTD_ErrorCode`, for accurate error handling. - `ZSTD_STATIC_LINKING_ONLY` : if this macro is defined _before_ including `zstd.h`, it unlocks access to the experimental API, exposed in the second part of `zstd.h`. All definitions in the experimental APIs are unstable, they may still change in the future, or even be removed. As a consequence, experimental definitions 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 within `libzstd`. The file structure is designed to make this selection manually achievable for any build system : - 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` : makes it possible 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". Conversely, `ZSTD_LEGACY_SUPPORT=0` means "do __not__ support legacy formats". By default, this build macro is set as `ZSTD_LEGACY_SUPPORT=5`. Decoding supported legacy format is a transparent capability triggered within decompression functions. It's also allowed to invoke legacy API directly, exposed in `lib/legacy/zstd_legacy.h`. Each version does also provide its own set of advanced API. For example, advanced API for version `v0.4` is exposed in `lib/legacy/zstd_v04.h` . - While invoking `make libzstd`, it's possible to define build macros `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 build 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`. - While invoking `make libzstd`, the build macro `ZSTD_LEGACY_MULTITHREADED_API=1` will expose the deprecated the `ZSTDMT` API exposed by `zstdmt_compress.h` in the shared library, which is now hidden by default. #### 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 : - `BUCK` : support for `buck` build system (https://buckbuild.com/) - `Makefile` : `make` script to build and install zstd library (static and dynamic) - `README.md` : this file - `dll/` : resources directory for Windows compilation - `libzstd.pc.in` : script for `pkg-config` (used in `make install`)