README.md in extzstd-0.2

- old
+ new

@@ -1,52 +1,81 @@
 Zstandard library files
 ================================
 
-The __lib__ directory contains several directories.
-Depending on target use case, it's enough to include only files from relevant directories.
+The __lib__ directory is split into several sub-directories,
+in order to make it easier to select or exclude specific 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).
+- `make` : generates both static and dynamic libraries
+- `make install` : install libraries in default system directories
+
+
 #### API
 
-Zstandard's stable API is exposed within [zstd.h](zstd.h),
-at the root of `lib` directory.
+Zstandard's stable API is exposed within [lib/zstd.h](zstd.h).
 
 
 #### Advanced API
 
-Some additional API may be useful if you're looking into advanced features :
-- common/error_public.h : transforms `size_t` function results into an `enum`,
-                          for precise error handling.
-- ZSTD_STATIC_LINKING_ONLY : if you define this macro _before_ including `zstd.h`,
-                          it will give access to advanced and experimental API.
+Optional advanced features are exposed via :
+
+- `lib/common/zstd_errors.h` : translates `size_t` function results
+                              into an `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 shall ___never be used with dynamic library___ !
                           They are not "stable", their definition may change in the future.
                           Only static linking is allowed.
 
 
 #### Modular build
 
-Directory `common/` is required in all circumstances.
-You can select to support compression only, by just adding files from the `compress/` directory,
-In a similar way, you can build a decompressor-only library with the `decompress/` directory.
+- 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` .
 
-Other optional functionalities provided are :
 
-- `dictBuilder/`  : source files to create dictionaries.
-                    The API can be consulted in `dictBuilder/zdict.h`.
-                    This module also depends on `common/` and `compress/` .
+#### Multithreading support
 
-- `legacy/` : source code to decompress previous versions of zstd, starting from `v0.1`.
-              This module also depends on `common/` and `decompress/` .
-              Library compilation must include directive `ZSTD_LEGACY_SUPPORT = 1` .
-              The main API can be consulted in `legacy/zstd_legacy.h`.
-              Advanced API from each version can be found in their relevant header file.
-              For example, advanced API for version `v0.4` is in `legacy/zstd_v04.h` .
+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)
 
+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.
 
-#### Using MinGW+MSYS to create DLL
+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.
 
+
+#### 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.
@@ -57,21 +86,23 @@
     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`.
 
 
-#### Obsolete streaming API
+#### Deprecated API
 
-Streaming is now provided within `zstd.h`.
-Older streaming API is still available within `deprecated/zbuff.h`.
-It will be removed in a future version.
-Consider migrating code towards newer streaming API in `zstd.h`.
+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`.
 
 
 #### Miscellaneous
 
 The other files are not source code. There are :
 
- - LICENSE : contains the BSD license text
- - Makefile : script to compile or install zstd library (static and dynamic)
- - libzstd.pc.in : for pkg-config (`make install`)
- - README.md : this file
+ - `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`)
+ - `README.md` : this file