README.md
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
22When building with `make`, by default the dynamic library is multithreaded and static library is single-threaded (for compatibility reasons).
23
24Enabling multithreading requires 2 conditions :
25- set build macro `ZSTD_MULTITHREAD` (`-DZSTD_MULTITHREAD` for `gcc`)
26- for POSIX systems : compile with pthread (`-pthread` compilation flag for `gcc`)
27
28For convenience, we provide a build target to generate multi and single threaded libraries:
29- Force enable multithreading on both dynamic and static libraries by appending `-mt` to the target, e.g. `make lib-mt`.
30- Force disable multithreading on both dynamic and static libraries by appending `-nomt` to the target, e.g. `make lib-nomt`.
31- By default, as mentioned before, dynamic library is multithreaded, and static library is single-threaded, e.g. `make lib`.
32
33When linking a POSIX program with a multithreaded version of `libzstd`,
34note that it's necessary to invoke the `-pthread` flag during link stage.
35
36Multithreading capabilities are exposed
37via the [advanced API defined in `lib/zstd.h`](https://github.com/facebook/zstd/blob/v1.4.3/lib/zstd.h#L351).
38
39
40#### API
41
42Zstandard's stable API is exposed within [lib/zstd.h](zstd.h).
43
44
45#### Advanced API
46
47Optional advanced features are exposed via :
48
49- `lib/zstd_errors.h` : translates `size_t` function results
50 into a `ZSTD_ErrorCode`, for accurate error handling.
51
52- `ZSTD_STATIC_LINKING_ONLY` : if this macro is defined _before_ including `zstd.h`,
53 it unlocks access to the experimental API,
54 exposed in the second part of `zstd.h`.
55 All definitions in the experimental APIs are unstable,
56 they may still change in the future, or even be removed.
57 As a consequence, experimental definitions shall ___never be used with dynamic library___ !
58 Only static linking is allowed.
59
60
61#### Modular build
62
63It's possible to compile only a limited set of features within `libzstd`.
64The file structure is designed to make this selection manually achievable for any build system :
65
66- Directory `lib/common` is always required, for all variants.
67
68- Compression source code lies in `lib/compress`
69
70- Decompression source code lies in `lib/decompress`
71
72- It's possible to include only `compress` or only `decompress`, they don't depend on each other.
73
74- `lib/dictBuilder` : makes it possible to generate dictionaries from a set of samples.
75 The API is exposed in `lib/dictBuilder/zdict.h`.
76 This module depends on both `lib/common` and `lib/compress` .
77
78- `lib/legacy` : makes it possible to decompress legacy zstd formats, starting from `v0.1.0`.
79 This module depends on `lib/common` and `lib/decompress`.
80 To enable this feature, define `ZSTD_LEGACY_SUPPORT` during compilation.
81 Specifying a number limits versions supported to that version onward.
82 For example, `ZSTD_LEGACY_SUPPORT=2` means : "support legacy formats >= v0.2.0".
83 Conversely, `ZSTD_LEGACY_SUPPORT=0` means "do __not__ support legacy formats".
84 By default, this build macro is set as `ZSTD_LEGACY_SUPPORT=5`.
85 Decoding supported legacy format is a transparent capability triggered within decompression functions.
86 It's also allowed to invoke legacy API directly, exposed in `lib/legacy/zstd_legacy.h`.
87 Each version does also provide its own set of advanced API.
88 For example, advanced API for version `v0.4` is exposed in `lib/legacy/zstd_v04.h` .
89
90- While invoking `make libzstd`, it's possible to define build macros
91 `ZSTD_LIB_COMPRESSION, ZSTD_LIB_DECOMPRESSION`, `ZSTD_LIB_DICTBUILDER`,
92 and `ZSTD_LIB_DEPRECATED` as `0` to forgo compilation of the
93 corresponding features. This will also disable compilation of all
94 dependencies (eg. `ZSTD_LIB_COMPRESSION=0` will also disable
95 dictBuilder).
96
97- There are a number of options that can help minimize the binary size of
98 `libzstd`.
99
100 The first step is to select the components needed (using the above-described
101 `ZSTD_LIB_COMPRESSION` etc.).
102
103 The next step is to set `ZSTD_LIB_MINIFY` to `1` when invoking `make`. This
104 disables various optional components and changes the compilation flags to
105 prioritize space-saving.
106
107 Detailed options: Zstandard's code and build environment is set up by default
108 to optimize above all else for performance. In pursuit of this goal, Zstandard
109 makes significant trade-offs in code size. For example, Zstandard often has
110 more than one implementation of a particular component, with each
111 implementation optimized for different scenarios. For example, the Huffman
112 decoder has complementary implementations that decode the stream one symbol at
113 a time or two symbols at a time. Zstd normally includes both (and dispatches
114 between them at runtime), but by defining `HUF_FORCE_DECOMPRESS_X1` or
115 `HUF_FORCE_DECOMPRESS_X2`, you can force the use of one or the other, avoiding
116 compilation of the other. Similarly, `ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT`
117 and `ZSTD_FORCE_DECOMPRESS_SEQUENCES_LONG` force the compilation and use of
118 only one or the other of two decompression implementations. The smallest
119 binary is achieved by using `HUF_FORCE_DECOMPRESS_X1` and
120 `ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT` (implied by `ZSTD_LIB_MINIFY`).
121
122 For squeezing the last ounce of size out, you can also define
123 `ZSTD_NO_INLINE`, which disables inlining, and `ZSTD_STRIP_ERROR_STRINGS`,
124 which removes the error messages that are otherwise returned by
125 `ZSTD_getErrorName` (implied by `ZSTD_LIB_MINIFY`).
126
127 Finally, when integrating into your application, make sure you're doing link-
128 time optimization and unused symbol garbage collection (via some combination of,
129 e.g., `-flto`, `-ffat-lto-objects`, `-fuse-linker-plugin`,
130 `-ffunction-sections`, `-fdata-sections`, `-fmerge-all-constants`,
131 `-Wl,--gc-sections`, `-Wl,-z,norelro`, and an archiver that understands
132 the compiler's intermediate representation, e.g., `AR=gcc-ar`). Consult your
133 compiler's documentation.
134
135- While invoking `make libzstd`, the build macro `ZSTD_LEGACY_MULTITHREADED_API=1`
136 will expose the deprecated `ZSTDMT` API exposed by `zstdmt_compress.h` in
137 the shared library, which is now hidden by default.
138
139- The build macro `DYNAMIC_BMI2` can be set to 1 or 0 in order to generate binaries
140 which can detect at runtime the presence of BMI2 instructions, and use them only if present.
141 These instructions contribute to better performance, notably on the decoder side.
142 By default, this feature is automatically enabled on detecting
143 the right instruction set (x64) and compiler (clang or gcc >= 5).
144 It's obviously disabled for different cpus,
145 or when BMI2 instruction set is _required_ by the compiler command line
146 (in this case, only the BMI2 code path is generated).
147 Setting this macro will either force to generate the BMI2 dispatcher (1)
148 or prevent it (0). It overrides automatic detection.
149
150- The build macro `ZSTD_NO_UNUSED_FUNCTIONS` can be defined to hide the definitions of functions
151 that zstd does not use. Not all unused functions are hidden, but they can be if needed.
152 Currently, this macro will hide function definitions in FSE and HUF that use an excessive
153 amount of stack space.
154
155- The build macro `ZSTD_NO_INTRINSICS` can be defined to disable all explicit intrinsics.
156 Compiler builtins are still used.
157
158- The build macro `ZSTD_DECODER_INTERNAL_BUFFER` can be set to control
159 the amount of extra memory used during decompression to store literals.
160 This defaults to 64kB. Reducing this value reduces the memory footprint of
161 `ZSTD_DCtx` decompression contexts,
162 but might also result in a small decompression speed cost.
163
164
165#### Windows : using MinGW+MSYS to create DLL
166
167DLL can be created using MinGW+MSYS with the `make libzstd` command.
168This command creates `dll\libzstd.dll` and the import library `dll\libzstd.lib`.
169The import library is only required with Visual C++.
170The header file `zstd.h` and the dynamic library `dll\libzstd.dll` are required to
171compile a project using gcc/MinGW.
172The dynamic library has to be added to linking options.
173It means that if a project that uses ZSTD consists of a single `test-dll.c`
174file it should be linked with `dll\libzstd.dll`. For example:
175```
176 gcc $(CFLAGS) -Iinclude/ test-dll.c -o test-dll dll\libzstd.dll
177```
178The compiled executable will require ZSTD DLL which is available at `dll\libzstd.dll`.
179
180
181#### Advanced Build options
182
183The build system requires a hash function in order to
184separate object files created with different compilation flags.
185By default, it tries to use `md5sum` or equivalent.
186The hash function can be manually switched by setting the `HASH` variable.
187For example : `make HASH=xxhsum`
188The hash function needs to generate at least 64-bit using hexadecimal format.
189When no hash function is found,
190the Makefile just generates all object files into the same default directory,
191irrespective of compilation flags.
192This functionality only matters if `libzstd` is compiled multiple times
193with different build flags.
194
195The build directory, where object files are stored
196can also be manually controlled using variable `BUILD_DIR`,
197for example `make BUILD_DIR=objectDir/v1`.
198In which case, the hash function doesn't matter.
199
200
201#### Deprecated API
202
203Obsolete API on their way out are stored in directory `lib/deprecated`.
204At this stage, it contains older streaming prototypes, in `lib/deprecated/zbuff.h`.
205These prototypes will be removed in some future version.
206Consider migrating code towards supported streaming API exposed in `zstd.h`.
207
208
209#### Miscellaneous
210
211The other files are not source code. There are :
212
213 - `BUCK` : support for `buck` build system (https://buckbuild.com/)
214 - `Makefile` : `make` script to build and install zstd library (static and dynamic)
215 - `README.md` : this file
216 - `dll/` : resources directory for Windows compilation
217 - `libzstd.pc.in` : script for `pkg-config` (used in `make install`)
218