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 (e.g. `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 On the compressor side, Zstd's compression levels map to several internal
123 strategies. In environments where the higher compression levels aren't used,
124 it is possible to exclude all but the fastest strategy with
125 `ZSTD_LIB_EXCLUDE_COMPRESSORS_DFAST_AND_UP=1`. (Note that this will change
126 the behavior of the default compression level.) Or if you want to retain the
127 default compressor as well, you can set
128 `ZSTD_LIB_EXCLUDE_COMPRESSORS_GREEDY_AND_UP=1`, at the cost of an additional
129 ~20KB or so.
130
131 For squeezing the last ounce of size out, you can also define
132 `ZSTD_NO_INLINE`, which disables inlining, and `ZSTD_STRIP_ERROR_STRINGS`,
133 which removes the error messages that are otherwise returned by
134 `ZSTD_getErrorName` (implied by `ZSTD_LIB_MINIFY`).
135
136 Finally, when integrating into your application, make sure you're doing link-
137 time optimization and unused symbol garbage collection (via some combination of,
138 e.g., `-flto`, `-ffat-lto-objects`, `-fuse-linker-plugin`,
139 `-ffunction-sections`, `-fdata-sections`, `-fmerge-all-constants`,
140 `-Wl,--gc-sections`, `-Wl,-z,norelro`, and an archiver that understands
141 the compiler's intermediate representation, e.g., `AR=gcc-ar`). Consult your
142 compiler's documentation.
143
144- While invoking `make libzstd`, the build macro `ZSTD_LEGACY_MULTITHREADED_API=1`
145 will expose the deprecated `ZSTDMT` API exposed by `zstdmt_compress.h` in
146 the shared library, which is now hidden by default.
147
148- The build macro `DYNAMIC_BMI2` can be set to 1 or 0 in order to generate binaries
149 which can detect at runtime the presence of BMI2 instructions, and use them only if present.
150 These instructions contribute to better performance, notably on the decoder side.
151 By default, this feature is automatically enabled on detecting
152 the right instruction set (x64) and compiler (clang or gcc >= 5).
153 It's obviously disabled for different cpus,
154 or when BMI2 instruction set is _required_ by the compiler command line
155 (in this case, only the BMI2 code path is generated).
156 Setting this macro will either force to generate the BMI2 dispatcher (1)
157 or prevent it (0). It overrides automatic detection.
158
159- The build macro `ZSTD_NO_UNUSED_FUNCTIONS` can be defined to hide the definitions of functions
160 that zstd does not use. Not all unused functions are hidden, but they can be if needed.
161 Currently, this macro will hide function definitions in FSE and HUF that use an excessive
162 amount of stack space.
163
164- The build macro `ZSTD_NO_INTRINSICS` can be defined to disable all explicit intrinsics.
165 Compiler builtins are still used.
166
167- The build macro `ZSTD_DECODER_INTERNAL_BUFFER` can be set to control
168 the amount of extra memory used during decompression to store literals.
169 This defaults to 64kB. Reducing this value reduces the memory footprint of
170 `ZSTD_DCtx` decompression contexts,
171 but might also result in a small decompression speed cost.
172
173- The C compiler macros `ZSTDLIB_VISIBLE`, `ZSTDERRORLIB_VISIBLE` and `ZDICTLIB_VISIBLE`
174 can be overridden to control the visibility of zstd's API. Additionally,
175 `ZSTDLIB_STATIC_API` and `ZDICTLIB_STATIC_API` can be overridden to control the visibility
176 of zstd's static API. Specifically, it can be set to `ZSTDLIB_HIDDEN` to hide the symbols
177 from the shared library. These macros default to `ZSTDLIB_VISIBILITY`,
178 `ZSTDERRORLIB_VSIBILITY`, and `ZDICTLIB_VISIBILITY` if unset, for backwards compatibility
179 with the old macro names.
180
181- The C compiler macro `HUF_DISABLE_FAST_DECODE` disables the newer Huffman fast C
182 and assembly decoding loops. You may want to use this macro if these loops are
183 slower on your platform.
184
185#### Windows : using MinGW+MSYS to create DLL
186
187DLL can be created using MinGW+MSYS with the `make libzstd` command.
188This command creates `dll\libzstd.dll` and the import library `dll\libzstd.lib`.
189The import library is only required with Visual C++.
190The header file `zstd.h` and the dynamic library `dll\libzstd.dll` are required to
191compile a project using gcc/MinGW.
192The dynamic library has to be added to linking options.
193It means that if a project that uses ZSTD consists of a single `test-dll.c`
194file it should be linked with `dll\libzstd.dll`. For example:
195```
196 gcc $(CFLAGS) -Iinclude/ test-dll.c -o test-dll dll\libzstd.dll
197```
198The compiled executable will require ZSTD DLL which is available at `dll\libzstd.dll`.
199
200
201#### Advanced Build options
202
203The build system requires a hash function in order to
204separate object files created with different compilation flags.
205By default, it tries to use `md5sum` or equivalent.
206The hash function can be manually switched by setting the `HASH` variable.
207For example : `make HASH=xxhsum`
208The hash function needs to generate at least 64-bit using hexadecimal format.
209When no hash function is found,
210the Makefile just generates all object files into the same default directory,
211irrespective of compilation flags.
212This functionality only matters if `libzstd` is compiled multiple times
213with different build flags.
214
215The build directory, where object files are stored
216can also be manually controlled using variable `BUILD_DIR`,
217for example `make BUILD_DIR=objectDir/v1`.
218In which case, the hash function doesn't matter.
219
220
221#### Deprecated API
222
223Obsolete API on their way out are stored in directory `lib/deprecated`.
224At this stage, it contains older streaming prototypes, in `lib/deprecated/zbuff.h`.
225These prototypes will be removed in some future version.
226Consider migrating code towards supported streaming API exposed in `zstd.h`.
227
228
229#### Miscellaneous
230
231The other files are not source code. There are :
232
233 - `BUCK` : support for `buck` build system (https://buckbuild.com/)
234 - `Makefile` : `make` script to build and install zstd library (static and dynamic)
235 - `README.md` : this file
236 - `dll/` : resources directory for Windows compilation
237 - `libzstd.pc.in` : script for `pkg-config` (used in `make install`)
238