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updated libzstd documentation

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Yann Collet 2018-12-25 03:10:07 -08:00
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1 changed files with 54 additions and 46 deletions
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@ -7,13 +7,32 @@ in order to make it easier to select or exclude features.
#### Building
`Makefile` script is provided, supporting all standard [Makefile conventions](https://www.gnu.org/prep/standards/html_node/Makefile-Conventions.html#Makefile-Conventions),
`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 in default system directories
- `make install` : install libraries and headers in target system directories
`libzstd` default scope includes compression, decompression, dictionary building,
and decoding support for legacy formats >= v0.5.0.
`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).
This API is still labelled experimental,
but is expected to become "stable" in the near future.
#### API
@ -26,47 +45,53 @@ Zstandard's stable API is exposed within [lib/zstd.h](zstd.h).
Optional advanced features are exposed via :
- `lib/common/zstd_errors.h` : translates `size_t` function results
into an `ZSTD_ErrorCode`, for accurate error handling.
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 advanced experimental API,
exposed in second part of `zstd.h`.
These APIs are not "stable", their definition may change in the future.
As a consequence, it shall ___never be used with dynamic library___ !
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.
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` : source code to decompress legacy zstd formats, starting from `v0.1.0`.
- `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".
`ZSTD_LEGACY_SUPPORT=3` means : "support legacy formats >= v0.3.0", and so on.
Currently, the default library setting is `ZST_LEGACY_SUPPORT=5`.
It can be changed at build by any other value.
Note that any number >= 8 translates into "do __not__ support legacy formats",
since all versions of `zstd` >= v0.8 are compatible with v1+ specification.
`ZSTD_LEGACY_SUPPORT=0` also means "do __not__ support legacy formats".
Once enabled, this capability is transparently triggered within decompression functions.
It's also possible to invoke directly legacy API, as exposed in `lib/legacy/zstd_legacy.h`.
Each version also provides an additional dedicated set of advanced API.
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` .
Note : `lib/legacy` only supports _decoding_ legacy formats.
- Similarly, you can define `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 macros that can be used to minify the decoder.
- 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
@ -86,23 +111,6 @@ It's possible to compile only a limited set of features.
`ZSTD_getErrorName`.
#### Multithreading support
Multithreading is disabled by default when building with `make`.
Enabling multithreading requires 2 conditions :
- set macro `ZSTD_MULTITHREAD`
- on POSIX systems : compile with pthread (`-pthread` compilation flag for `gcc`)
Both conditions are automatically triggered by invoking `make lib-mt` target.
Note that, when linking a POSIX program with a multithreaded version of `libzstd`,
it's necessary to trigger `-pthread` flag during link stage.
Multithreading capabilities are exposed
via [advanced API `ZSTD_compress_generic()` defined in `lib/zstd.h`](https://github.com/facebook/zstd/blob/dev/lib/zstd.h#L919).
This API is still considered experimental,
but is expected to become "stable" at some point in the future.
#### Windows : using MinGW+MSYS to create DLL
DLL can be created using MinGW+MSYS with the `make libzstd` command.
@ -131,8 +139,8 @@ Consider migrating code towards supported streaming API exposed in `zstd.h`.
The other files are not source code. There are :
- `LICENSE` : contains the BSD license text
- `Makefile` : `make` script to build and install zstd library (static and dynamic)
- `BUCK` : support for `buck` build system (https://buckbuild.com/)
- `libzstd.pc.in` : for `pkg-config` (used in `make install`)
- `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`)