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updated /lib documentation

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Yann Collet
2017-12-31 15:50:00 +01:00
parent b6887b6d43
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lib/README.md
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@@ -2,16 +2,19 @@ Zstandard library files
================================
The __lib__ directory is split into several sub-directories,
in order to make it easier to select or exclude specific features.
in order to make it easier to select or exclude features.
#### Building
`Makefile` script is provided, supporting the standard set of commands,
directories, and variables (see https://www.gnu.org/prep/standards/html_node/Command-Variables.html).
`Makefile` script is provided, supporting all standard [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
`libzstd` default scope includes compression, decompression, dictionary building,
and decoding support for legacy formats >= v0.4.0.
#### API
@@ -27,29 +30,37 @@ Optional advanced features are exposed via :
- `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 shall ___never be used with dynamic library___ !
They are not "stable", their definition may change in the future.
These APIs are not "stable", their definition may change in the future.
As a consequencem, it 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.
- 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 older zstd formats, starting from `v0.1`.
This module depends on `lib/common` and `lib/decompress`.
To enable this feature, it's necessary to define `ZSTD_LEGACY_SUPPORT = 1` during compilation.
Typically, with `gcc`, add argument `-DZSTD_LEGACY_SUPPORT=1`.
Using higher number limits the number of version supported.
For example, `ZSTD_LEGACY_SUPPORT=2` means : "support legacy formats starting from v0.2+".
The API is exposed in `lib/legacy/zstd_legacy.h`.
Each version also provides a (dedicated) set of advanced API.
For example, advanced API for version `v0.4` is exposed in `lib/legacy/zstd_v04.h` .
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`.
This module depends on `lib/common` and `lib/decompress`.
To enable this feature, it's required to define `ZSTD_LEGACY_SUPPORT` during compilation.
Typically, with `gcc`, add argument `-DZSTD_LEGACY_SUPPORT=1`.
Using higher number limits versions supported.
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.
Starting v0.8.0, all versions of `zstd` produce frames compliant with specification.
As a consequence, `ZSTD_LEGACY_SUPPORT=8` (or more) doesn't trigger legacy support.
Also, `ZSTD_LEGACY_SUPPORT=0` 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.
For example, advanced API for version `v0.4` is exposed in `lib/legacy/zstd_v04.h` .
Note : `lib/legacy` only supports _decoding_ legacy formats.
#### Multithreading support
@@ -57,19 +68,16 @@ Optional advanced features are exposed via :
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` for example)
- 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 :
- private API `lib/compress/zstdmt_compress.h`.
Symbols defined in this header are currently exposed in `libzstd`, hence usable.
Note however that this API is planned to be locked and remain strictly internal in the future.
- advanced API `ZSTD_compress_generic()`, defined in `lib/zstd.h`, experimental section.
This API is still considered experimental, but is designed to be labelled "stable" at some point in the future.
It's the recommended entry point for multi-threading operations.
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
@@ -92,7 +100,6 @@ The compiled executable will require ZSTD DLL which is available at `dll\libzstd
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`.
Presence in this directory is temporary.
These prototypes will be removed in some future version.
Consider migrating code towards supported streaming API exposed in `zstd.h`.