updated /lib documentation

diff --git a/lib/README.md b/lib/README.md
index df136c4867d21df211cf846e5ab932be5853a478..8a13b4e3d604ffe75b1b8b339b59b763d9ad92bb 100644 (file)
--- a/lib/README.md
+++ b/lib/README.md
@@ -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`.