13c5ec3e41
The load algorithm requires we do it all in one go. |
||
---|---|---|
.. | ||
common | ||
compress | ||
decompress | ||
deprecated | ||
dictBuilder | ||
dll/example | ||
legacy | ||
.gitignore | ||
BUCK | ||
libzstd.pc.in | ||
Makefile | ||
README.md | ||
zstd.h |
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,
including commands variables, staged install, directory variables and standard targets.
make
: generates both static and dynamic librariesmake 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
forgcc
) - for POSIX systems : compile with pthread (
-pthread
compilation flag forgcc
)
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 invoke the -pthread
flag during link stage.
Multithreading capabilities are exposed
via the advanced API defined in lib/zstd.h
.
API
Zstandard's stable API is exposed within lib/zstd.h.
Advanced API
Optional advanced features are exposed via :
-
lib/common/zstd_errors.h
: translatessize_t
function results into aZSTD_ErrorCode
, for accurate error handling. -
ZSTD_STATIC_LINKING_ONLY
: if this macro is defined before includingzstd.h
, it unlocks access to the experimental API, exposed in the second part ofzstd.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 onlydecompress
, they don't depend on each other. -
lib/dictBuilder
: makes it possible to generate dictionaries from a set of samples. The API is exposed inlib/dictBuilder/zdict.h
. This module depends on bothlib/common
andlib/compress
. -
lib/legacy
: makes it possible to decompress legacy zstd formats, starting fromv0.1.0
. This module depends onlib/common
andlib/decompress
. To enable this feature, defineZSTD_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 asZSTD_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 inlib/legacy/zstd_legacy.h
. Each version does also provide its own set of advanced API. For example, advanced API for versionv0.4
is exposed inlib/legacy/zstd_v04.h
. -
While invoking
make libzstd
, it's possible to define build macrosZSTD_LIB_COMPRESSION, ZSTD_LIB_DECOMPRESSION
,ZSTD_LIB_DICTBUILDER
, andZSTD_LIB_DEPRECATED
as0
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 a number of options that can help minimize the binary size of
libzstd
.The first step is to select the components needed (using the above-described
ZSTD_LIB_COMPRESSION
etc.).The next step is to set
ZSTD_LIB_MINIFY
to1
when invokingmake
. This disables various optional components and changes the compilation flags to prioritize space-saving.Detailed options: Zstandard's code and build environment is set up by default to optimize above all else for performance. In pursuit of this goal, Zstandard makes significant trade-offs in code size. For example, Zstandard often has more than one implementation of a particular component, with each implementation optimized 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
orHUF_FORCE_DECOMPRESS_X2
, you can force the use of one or the other, avoiding compilation of the other. Similarly,ZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT
andZSTD_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 usingHUF_FORCE_DECOMPRESS_X1
andZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT
(implied byZSTD_LIB_MINIFY
).For squeezing the last ounce of size out, you can also define
ZSTD_NO_INLINE
, which disables inlining, andZSTD_STRIP_ERROR_STRINGS
, which removes the error messages that are otherwise returned byZSTD_getErrorName
(implied byZSTD_LIB_MINIFY
).Finally, when integrating into your application, make sure you're doing link- time optimation and unused symbol garbage collection (via some combination of, e.g.,
-flto
,-ffat-lto-objects
,-fuse-linker-plugin
,-ffunction-sections
,-fdata-sections
,-fmerge-all-constants
,-Wl,--gc-sections
,-Wl,-z,norelro
, and an archiver that understands the compiler's intermediate representation, e.g.,AR=gcc-ar
). Consult your compiler's documentation. -
While invoking
make libzstd
, the build macroZSTD_LEGACY_MULTITHREADED_API=1
will expose the deprecatedZSTDMT
API exposed byzstdmt_compress.h
in the shared library, which is now hidden by default. -
The build macro
DYNAMIC_BMI2
can be set to 1 or 0 in order to generate binaries which can detect at runtime the presence of BMI2 instructions, and use them only if present. These instructions contribute to better performance, notably on the decoder side. By default, this feature is automatically enabled on detecting the right instruction set (x64) and compiler (clang or gcc >= 5). It's obviously disabled for different cpus, or when BMI2 instruction set is required by the compiler command line (in this case, only the BMI2 code path is generated). Setting this macro will either force to generate the BMI2 dispatcher (1) or prevent it (0). It overrides automatic detection. -
The build macro
ZSTD_NO_UNUSED_FUNCTIONS
can be defined to hide the definitions of functions that zstd does not use. Not all unused functions are hidden, but they can be if needed. Currently, this macro will hide function definitions in FSE and HUF that use an excessive amount of stack space. -
The build macro
ZSTD_NO_INTRINSICS
can be defined to disable all explicit intrinsics. Compiler builtins are still used.
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 forbuck
build system (https://buckbuild.com/)Makefile
:make
script to build and install zstd library (static and dynamic)README.md
: this filedll/
: resources directory for Windows compilationlibzstd.pc.in
: script forpkg-config
(used inmake install
)