1Zstandard library files 2================================ 3 4The __lib__ directory is split into several sub-directories, 5in order to make it easier to select or exclude features. 6 7 8#### Building 9 10`Makefile` script is provided, supporting [Makefile conventions](https://www.gnu.org/prep/standards/html_node/Makefile-Conventions.html#Makefile-Conventions), 11including commands variables, staged install, directory variables and standard targets. 12- `make` : generates both static and dynamic libraries 13- `make install` : install libraries and headers in target system directories 14 15`libzstd` default scope is pretty large, including compression, decompression, dictionary builder, 16and support for decoding legacy formats >= v0.5.0. 17The scope can be reduced on demand (see paragraph _modular build_). 18 19 20#### Multithreading support 21 22Multithreading is disabled by default when building with `make`. 23Enabling multithreading requires 2 conditions : 24- set build macro `ZSTD_MULTITHREAD` (`-DZSTD_MULTITHREAD` for `gcc`) 25- for POSIX systems : compile with pthread (`-pthread` compilation flag for `gcc`) 26 27Both conditions are automatically applied when invoking `make lib-mt` target. 28 29When linking a POSIX program with a multithreaded version of `libzstd`, 30note that it's necessary to request the `-pthread` flag during link stage. 31 32Multithreading capabilities are exposed 33via the [advanced API defined in `lib/zstd.h`](https://github.com/facebook/zstd/blob/v1.3.8/lib/zstd.h#L592). 34This API is still labelled experimental, 35but is expected to become "stable" in the near future. 36 37 38#### API 39 40Zstandard's stable API is exposed within [lib/zstd.h](zstd.h). 41 42 43#### Advanced API 44 45Optional advanced features are exposed via : 46 47- `lib/common/zstd_errors.h` : translates `size_t` function results 48 into a `ZSTD_ErrorCode`, for accurate error handling. 49 50- `ZSTD_STATIC_LINKING_ONLY` : if this macro is defined _before_ including `zstd.h`, 51 it unlocks access to the experimental API, 52 exposed in the second part of `zstd.h`. 53 All definitions in the experimental APIs are unstable, 54 they may still change in the future, or even be removed. 55 As a consequence, experimental definitions shall ___never be used with dynamic library___ ! 56 Only static linking is allowed. 57 58 59#### Modular build 60 61It's possible to compile only a limited set of features within `libzstd`. 62The file structure is designed to make this selection manually achievable for any build system : 63 64- Directory `lib/common` is always required, for all variants. 65 66- Compression source code lies in `lib/compress` 67 68- Decompression source code lies in `lib/decompress` 69 70- It's possible to include only `compress` or only `decompress`, they don't depend on each other. 71 72- `lib/dictBuilder` : makes it possible to generate dictionaries from a set of samples. 73 The API is exposed in `lib/dictBuilder/zdict.h`. 74 This module depends on both `lib/common` and `lib/compress` . 75 76- `lib/legacy` : makes it possible to decompress legacy zstd formats, starting from `v0.1.0`. 77 This module depends on `lib/common` and `lib/decompress`. 78 To enable this feature, define `ZSTD_LEGACY_SUPPORT` during compilation. 79 Specifying a number limits versions supported to that version onward. 80 For example, `ZSTD_LEGACY_SUPPORT=2` means : "support legacy formats >= v0.2.0". 81 Conversely, `ZSTD_LEGACY_SUPPORT=0` means "do __not__ support legacy formats". 82 By default, this build macro is set as `ZSTD_LEGACY_SUPPORT=5`. 83 Decoding supported legacy format is a transparent capability triggered within decompression functions. 84 It's also allowed to invoke legacy API directly, exposed in `lib/legacy/zstd_legacy.h`. 85 Each version does also provide its own set of advanced API. 86 For example, advanced API for version `v0.4` is exposed in `lib/legacy/zstd_v04.h` . 87 88- While invoking `make libzstd`, it's possible to define build macros 89 `ZSTD_LIB_COMPRESSION, ZSTD_LIB_DECOMPRESSION`, `ZSTD_LIB_DICTBUILDER`, 90 and `ZSTD_LIB_DEPRECATED` as `0` to forgo compilation of the corresponding features. 91 This will also disable compilation of all dependencies 92 (eg. `ZSTD_LIB_COMPRESSION=0` will also disable dictBuilder). 93 94- There are some additional build macros that can be used to minify the decoder. 95 96 Zstandard often has more than one implementation of a piece of functionality, 97 where each implementation optimizes for different scenarios. For example, the 98 Huffman decoder has complementary implementations that decode the stream one 99 symbol at a time or two symbols at a time. Zstd normally includes both (and 100 dispatches between them at runtime), but by defining `HUF_FORCE_DECOMPRESS_X1` 101 or `HUF_FORCE_DECOMPRESS_X2`, you can force the use of one or the other, avoiding 102 compilation of the other. Similarly, `ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT` 103 and `ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG` force the compilation and use of 104 only one or the other of two decompression implementations. The smallest 105 binary is achieved by using `HUF_FORCE_DECOMPRESS_X1` and 106 `ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT`. 107 108 For squeezing the last ounce of size out, you can also define 109 `ZSTD_NO_INLINE`, which disables inlining, and `ZSTD_STRIP_ERROR_STRINGS`, 110 which removes the error messages that are otherwise returned by 111 `ZSTD_getErrorName`. 112 113 114#### Windows : using MinGW+MSYS to create DLL 115 116DLL can be created using MinGW+MSYS with the `make libzstd` command. 117This command creates `dll\libzstd.dll` and the import library `dll\libzstd.lib`. 118The import library is only required with Visual C++. 119The header file `zstd.h` and the dynamic library `dll\libzstd.dll` are required to 120compile a project using gcc/MinGW. 121The dynamic library has to be added to linking options. 122It means that if a project that uses ZSTD consists of a single `test-dll.c` 123file it should be linked with `dll\libzstd.dll`. For example: 124``` 125 gcc $(CFLAGS) -Iinclude/ test-dll.c -o test-dll dll\libzstd.dll 126``` 127The compiled executable will require ZSTD DLL which is available at `dll\libzstd.dll`. 128 129 130#### Deprecated API 131 132Obsolete API on their way out are stored in directory `lib/deprecated`. 133At this stage, it contains older streaming prototypes, in `lib/deprecated/zbuff.h`. 134These prototypes will be removed in some future version. 135Consider migrating code towards supported streaming API exposed in `zstd.h`. 136 137 138#### Miscellaneous 139 140The other files are not source code. There are : 141 142 - `BUCK` : support for `buck` build system (https://buckbuild.com/) 143 - `Makefile` : `make` script to build and install zstd library (static and dynamic) 144 - `README.md` : this file 145 - `dll/` : resources directory for Windows compilation 146 - `libzstd.pc.in` : script for `pkg-config` (used in `make install`) 147