zstd: import usptream v1.5.2

Updates the kernel's zstd library to v1.5.2, the latest zstd release.
The upstream tag it is updated to is `v1.5.2-kernel`, which contains
several cherry-picked commits on top of the v1.5.2 release which are
required for the kernel update. I will create this tag once the PR is
ready to merge, until then reference the temporary upstream branch
`v1.5.2-kernel-cherrypicks`.

I plan to submit this patch as part of the v6.2 merge window.

I've done basic build testing & testing on x86-64, i386, and aarch64.
I'm merging these patches into my `zstd-next` branch, which is pulled
into `linux-next` for further testing.

I've benchmarked BtrFS with zstd compression on a x86-64 machine, and
saw these results. Decompression speed is a small win across the board.
The lower compression levels 1-4 see both compression speed and
compression ratio wins. The higher compression levels see a small
compression speed loss and about neutral ratio. I expect the lower
compression levels to be used much more heavily than the high
compression levels, so this should be a net win.

Level	CTime	DTime	Ratio
1	-2.95%	-1.1%	-0.7%
3	-3.5%	-1.2%	-0.5%
5	+3.7%	-1.0%	+0.0%
7	+3.2%	-0.9%	+0.0%
9	-4.3%	-0.8%	+0.1%

Signed-off-by: Nick Terrell <terrelln@fb.com>

36 files changed, 6951 insertions, 2605 deletions

diff --git a/include/linux/zstd_lib.h b/include/linux/zstd_lib.h
index 6b91758b61af..79d55465d5c1 100644
--- a/include/linux/zstd_lib.h
+++ b/include/linux/zstd_lib.h
@@ -17,8 +17,16 @@
 
 
 /* =====   ZSTDLIB_API : control library symbols visibility   ===== */
-#define ZSTDLIB_VISIBILITY 
-#define ZSTDLIB_API ZSTDLIB_VISIBILITY
+#ifndef ZSTDLIB_VISIBLE
+#  if (__GNUC__ >= 4) && !defined(__MINGW32__)
+#    define ZSTDLIB_VISIBLE __attribute__ ((visibility ("default")))
+#    define ZSTDLIB_HIDDEN __attribute__ ((visibility ("hidden")))
+#  else
+#    define ZSTDLIB_VISIBLE
+#    define ZSTDLIB_HIDDEN
+#  endif
+#endif
+#define ZSTDLIB_API ZSTDLIB_VISIBLE
 
 
 /* *****************************************************************************
@@ -56,8 +64,8 @@
 
 /*------   Version   ------*/
 #define ZSTD_VERSION_MAJOR    1
-#define ZSTD_VERSION_MINOR    4
-#define ZSTD_VERSION_RELEASE  10
+#define ZSTD_VERSION_MINOR    5
+#define ZSTD_VERSION_RELEASE  2
 #define ZSTD_VERSION_NUMBER  (ZSTD_VERSION_MAJOR *100*100 + ZSTD_VERSION_MINOR *100 + ZSTD_VERSION_RELEASE)
 
 /*! ZSTD_versionNumber() :
@@ -94,7 +102,6 @@ ZSTDLIB_API const char* ZSTD_versionString(void);
 #define ZSTD_BLOCKSIZE_MAX     (1<<ZSTD_BLOCKSIZELOG_MAX)
 
 
-
 /* *************************************
 *  Simple API
 ***************************************/
@@ -151,7 +158,7 @@ ZSTDLIB_API unsigned long long ZSTD_getFrameContentSize(const void *src, size_t
  * @return : decompressed size of `src` frame content _if known and not empty_, 0 otherwise. */
 ZSTDLIB_API unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
 
-/*! ZSTD_findFrameCompressedSize() :
+/*! ZSTD_findFrameCompressedSize() : Requires v1.4.0+
  * `src` should point to the start of a ZSTD frame or skippable frame.
  * `srcSize` must be >= first frame size
  * @return : the compressed size of the first frame starting at `src`,
@@ -165,8 +172,9 @@ ZSTDLIB_API size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize)
 ZSTDLIB_API size_t      ZSTD_compressBound(size_t srcSize); /*!< maximum compressed size in worst case single-pass scenario */
 ZSTDLIB_API unsigned    ZSTD_isError(size_t code);          /*!< tells if a `size_t` function result is an error code */
 ZSTDLIB_API const char* ZSTD_getErrorName(size_t code);     /*!< provides readable string from an error code */
-ZSTDLIB_API int         ZSTD_minCLevel(void);               /*!< minimum negative compression level allowed */
+ZSTDLIB_API int         ZSTD_minCLevel(void);               /*!< minimum negative compression level allowed, requires v1.4.0+ */
 ZSTDLIB_API int         ZSTD_maxCLevel(void);               /*!< maximum compression level available */
+ZSTDLIB_API int         ZSTD_defaultCLevel(void);           /*!< default compression level, specified by ZSTD_CLEVEL_DEFAULT, requires v1.5.0+ */
 
 
 /* *************************************
@@ -219,9 +227,9 @@ ZSTDLIB_API size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx,
                                  const void* src, size_t srcSize);
 
 
-/* *************************************
-*  Advanced compression API
-***************************************/
+/* *******************************************
+*  Advanced compression API (Requires v1.4.0+)
+**********************************************/
 
 /* API design :
  *   Parameters are pushed one by one into an existing context,
@@ -232,7 +240,7 @@ ZSTDLIB_API size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx,
  *
  *   It's possible to reset all parameters to "default" using ZSTD_CCtx_reset().
  *
- *   This API supercedes all other "advanced" API entry points in the experimental section.
+ *   This API supersedes all other "advanced" API entry points in the experimental section.
  *   In the future, we expect to remove from experimental API entry points which are redundant with this API.
  */
 
@@ -251,7 +259,6 @@ typedef enum { ZSTD_fast=1,
                          Only the order (from fast to strong) is guaranteed */
 } ZSTD_strategy;
 
-
 typedef enum {
 
     /* compression parameters
@@ -317,7 +324,6 @@ typedef enum {
                               * The higher the value of selected strategy, the more complex it is,
                               * resulting in stronger and slower compression.
                               * Special: value 0 means "use default strategy". */
-
     /* LDM mode parameters */
     ZSTD_c_enableLongDistanceMatching=160, /* Enable long distance matching.
                                      * This parameter is designed to improve compression ratio
@@ -374,7 +380,7 @@ typedef enum {
     ZSTD_c_jobSize=401,      /* Size of a compression job. This value is enforced only when nbWorkers >= 1.
                               * Each compression job is completed in parallel, so this value can indirectly impact the nb of active threads.
                               * 0 means default, which is dynamically determined based on compression parameters.
-                              * Job size must be a minimum of overlap size, or 1 MB, whichever is largest.
+                              * Job size must be a minimum of overlap size, or ZSTDMT_JOBSIZE_MIN (= 512 KB), whichever is largest.
                               * The minimum size is automatically and transparently enforced. */
     ZSTD_c_overlapLog=402,   /* Control the overlap size, as a fraction of window size.
                               * The overlap size is an amount of data reloaded from previous job at the beginning of a new job.
@@ -404,6 +410,8 @@ typedef enum {
      * ZSTD_c_stableOutBuffer
      * ZSTD_c_blockDelimiters
      * ZSTD_c_validateSequences
+     * ZSTD_c_useBlockSplitter
+     * ZSTD_c_useRowMatchFinder
      * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them.
      * note : never ever use experimentalParam? names directly;
      *        also, the enums values themselves are unstable and can still change.
@@ -419,7 +427,10 @@ typedef enum {
      ZSTD_c_experimentalParam9=1006,
      ZSTD_c_experimentalParam10=1007,
      ZSTD_c_experimentalParam11=1008,
-     ZSTD_c_experimentalParam12=1009
+     ZSTD_c_experimentalParam12=1009,
+     ZSTD_c_experimentalParam13=1010,
+     ZSTD_c_experimentalParam14=1011,
+     ZSTD_c_experimentalParam15=1012
 } ZSTD_cParameter;
 
 typedef struct {
@@ -504,9 +515,9 @@ ZSTDLIB_API size_t ZSTD_compress2( ZSTD_CCtx* cctx,
                              const void* src, size_t srcSize);
 
 
-/* *************************************
-*  Advanced decompression API
-***************************************/
+/* *********************************************
+*  Advanced decompression API (Requires v1.4.0+)
+************************************************/
 
 /* The advanced API pushes parameters one by one into an existing DCtx context.
  * Parameters are sticky, and remain valid for all following frames
@@ -668,7 +679,7 @@ typedef enum {
                         : note : multithreaded compression will block to flush as much output as possible. */
 } ZSTD_EndDirective;
 
-/*! ZSTD_compressStream2() :
+/*! ZSTD_compressStream2() : Requires v1.4.0+
  *  Behaves about the same as ZSTD_compressStream, with additional control on end directive.
  *  - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
  *  - Compression parameters cannot be changed once compression is started (save a list of exceptions in multi-threading mode)
@@ -714,11 +725,11 @@ ZSTDLIB_API size_t ZSTD_CStreamOutSize(void);   /*< recommended size for output
 
 
 /* *****************************************************************************
- * This following is a legacy streaming API.
+ * This following is a legacy streaming API, available since v1.0+ .
  * It can be replaced by ZSTD_CCtx_reset() and ZSTD_compressStream2().
  * It is redundant, but remains fully supported.
- * Advanced parameters and dictionary compression can only be used through the
- * new API.
+ * Streaming in combination with advanced parameters and dictionary compression
+ * can only be used through the new API.
  ******************************************************************************/
 
 /*!
@@ -796,7 +807,7 @@ ZSTDLIB_API size_t ZSTD_DStreamOutSize(void);   /*!< recommended size for output
 /*! ZSTD_compress_usingDict() :
  *  Compression at an explicit compression level using a Dictionary.
  *  A dictionary can be any arbitrary data segment (also called a prefix),
- *  or a buffer with specified information (see dictBuilder/zdict.h).
+ *  or a buffer with specified information (see zdict.h).
  *  Note : This function loads the dictionary, resulting in significant startup delay.
  *         It's intended for a dictionary used only once.
  *  Note 2 : When `dict == NULL || dictSize < 8` no dictionary is used. */
@@ -879,19 +890,25 @@ ZSTDLIB_API size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
  *  Dictionary helper functions
  *******************************/
 
-/*! ZSTD_getDictID_fromDict() :
+/*! ZSTD_getDictID_fromDict() : Requires v1.4.0+
  *  Provides the dictID stored within dictionary.
  *  if @return == 0, the dictionary is not conformant with Zstandard specification.
  *  It can still be loaded, but as a content-only dictionary. */
 ZSTDLIB_API unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
 
-/*! ZSTD_getDictID_fromDDict() :
+/*! ZSTD_getDictID_fromCDict() : Requires v1.5.0+
+ *  Provides the dictID of the dictionary loaded into `cdict`.
+ *  If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
+ *  Non-conformant dictionaries can still be loaded, but as content-only dictionaries. */
+ZSTDLIB_API unsigned ZSTD_getDictID_fromCDict(const ZSTD_CDict* cdict);
+
+/*! ZSTD_getDictID_fromDDict() : Requires v1.4.0+
  *  Provides the dictID of the dictionary loaded into `ddict`.
  *  If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
  *  Non-conformant dictionaries can still be loaded, but as content-only dictionaries. */
 ZSTDLIB_API unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
 
-/*! ZSTD_getDictID_fromFrame() :
+/*! ZSTD_getDictID_fromFrame() : Requires v1.4.0+
  *  Provides the dictID required to decompressed the frame stored within `src`.
  *  If @return == 0, the dictID could not be decoded.
  *  This could for one of the following reasons :
@@ -905,16 +922,16 @@ ZSTDLIB_API unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
 
 
 /* *****************************************************************************
- * Advanced dictionary and prefix API
+ * Advanced dictionary and prefix API (Requires v1.4.0+)
  *
  * This API allows dictionaries to be used with ZSTD_compress2(),
- * ZSTD_compressStream2(), and ZSTD_decompress(). Dictionaries are sticky, and
+ * ZSTD_compressStream2(), and ZSTD_decompressDCtx(). Dictionaries are sticky, and
  * only reset with the context is reset with ZSTD_reset_parameters or
  * ZSTD_reset_session_and_parameters. Prefixes are single-use.
  ******************************************************************************/
 
 
-/*! ZSTD_CCtx_loadDictionary() :
+/*! ZSTD_CCtx_loadDictionary() : Requires v1.4.0+
  *  Create an internal CDict from `dict` buffer.
  *  Decompression will have to use same dictionary.
  * @result : 0, or an error code (which can be tested with ZSTD_isError()).
@@ -933,7 +950,7 @@ ZSTDLIB_API unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
  *           to precisely select how dictionary content must be interpreted. */
 ZSTDLIB_API size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);
 
-/*! ZSTD_CCtx_refCDict() :
+/*! ZSTD_CCtx_refCDict() : Requires v1.4.0+
  *  Reference a prepared dictionary, to be used for all next compressed frames.
  *  Note that compression parameters are enforced from within CDict,
  *  and supersede any compression parameter previously set within CCtx.
@@ -947,7 +964,7 @@ ZSTDLIB_API size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, s
  *  Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx. */
 ZSTDLIB_API size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict);
 
-/*! ZSTD_CCtx_refPrefix() :
+/*! ZSTD_CCtx_refPrefix() : Requires v1.4.0+
  *  Reference a prefix (single-usage dictionary) for next compressed frame.
  *  A prefix is **only used once**. Tables are discarded at end of frame (ZSTD_e_end).
  *  Decompression will need same prefix to properly regenerate data.
@@ -968,7 +985,7 @@ ZSTDLIB_API size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict);
 ZSTDLIB_API size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx,
                                  const void* prefix, size_t prefixSize);
 
-/*! ZSTD_DCtx_loadDictionary() :
+/*! ZSTD_DCtx_loadDictionary() : Requires v1.4.0+
  *  Create an internal DDict from dict buffer,
  *  to be used to decompress next frames.
  *  The dictionary remains valid for all future frames, until explicitly invalidated.
@@ -985,7 +1002,7 @@ ZSTDLIB_API size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx,
  */
 ZSTDLIB_API size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
 
-/*! ZSTD_DCtx_refDDict() :
+/*! ZSTD_DCtx_refDDict() : Requires v1.4.0+
  *  Reference a prepared dictionary, to be used to decompress next frames.
  *  The dictionary remains active for decompression of future frames using same DCtx.
  *
@@ -1003,7 +1020,7 @@ ZSTDLIB_API size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, s
  */
 ZSTDLIB_API size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict);
 
-/*! ZSTD_DCtx_refPrefix() :
+/*! ZSTD_DCtx_refPrefix() : Requires v1.4.0+
  *  Reference a prefix (single-usage dictionary) to decompress next frame.
  *  This is the reverse operation of ZSTD_CCtx_refPrefix(),
  *  and must use the same prefix as the one used during compression.
@@ -1024,7 +1041,7 @@ ZSTDLIB_API size_t ZSTD_DCtx_refPrefix(ZSTD_DCtx* dctx,
 
 /* ===   Memory management   === */
 
-/*! ZSTD_sizeof_*() :
+/*! ZSTD_sizeof_*() : Requires v1.4.0+
  *  These functions give the _current_ memory usage of selected object.
  *  Note that object memory usage can evolve (increase or decrease) over time. */
 ZSTDLIB_API size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
@@ -1049,6 +1066,29 @@ ZSTDLIB_API size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
 #if !defined(ZSTD_H_ZSTD_STATIC_LINKING_ONLY)
 #define ZSTD_H_ZSTD_STATIC_LINKING_ONLY
 
+/* This can be overridden externally to hide static symbols. */
+#ifndef ZSTDLIB_STATIC_API
+#define ZSTDLIB_STATIC_API ZSTDLIB_VISIBLE
+#endif
+
+/* Deprecation warnings :
+ * Should these warnings be a problem, it is generally possible to disable them,
+ * typically with -Wno-deprecated-declarations for gcc or _CRT_SECURE_NO_WARNINGS in Visual.
+ * Otherwise, it's also possible to define ZSTD_DISABLE_DEPRECATE_WARNINGS.
+ */
+#ifdef ZSTD_DISABLE_DEPRECATE_WARNINGS
+#  define ZSTD_DEPRECATED(message) ZSTDLIB_STATIC_API  /* disable deprecation warnings */
+#else
+#  if (defined(GNUC) && (GNUC > 4 || (GNUC == 4 && GNUC_MINOR >= 5))) || defined(__clang__)
+#    define ZSTD_DEPRECATED(message) ZSTDLIB_STATIC_API __attribute__((deprecated(message)))
+#  elif (__GNUC__ >= 3)
+#    define ZSTD_DEPRECATED(message) ZSTDLIB_STATIC_API __attribute__((deprecated))
+#  else
+#    pragma message("WARNING: You need to implement ZSTD_DEPRECATED for this compiler")
+#    define ZSTD_DEPRECATED(message) ZSTDLIB_STATIC_API
+#  endif
+#endif /* ZSTD_DISABLE_DEPRECATE_WARNINGS */
+
 /* **************************************************************************************
  *   experimental API (static linking only)
  ****************************************************************************************
@@ -1111,9 +1151,6 @@ ZSTDLIB_API size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
 #define ZSTD_SRCSIZEHINT_MIN        0
 #define ZSTD_SRCSIZEHINT_MAX        INT_MAX
 
-/* internal */
-#define ZSTD_HASHLOG3_MAX           17
-
 
 /* ---  Advanced types  --- */
 
@@ -1255,6 +1292,15 @@ typedef enum {
   ZSTD_lcm_uncompressed = 2   /*< Always emit uncompressed literals. */
 } ZSTD_literalCompressionMode_e;
 
+typedef enum {
+  /* Note: This enum controls features which are conditionally beneficial. Zstd typically will make a final
+   * decision on whether or not to enable the feature (ZSTD_ps_auto), but setting the switch to ZSTD_ps_enable
+   * or ZSTD_ps_disable allow for a force enable/disable the feature.
+   */
+  ZSTD_ps_auto = 0,         /* Let the library automatically determine whether the feature shall be enabled */
+  ZSTD_ps_enable = 1,       /* Force-enable the feature */
+  ZSTD_ps_disable = 2       /* Do not use the feature */
+} ZSTD_paramSwitch_e;
 
 /* *************************************
 *  Frame size functions
@@ -1281,7 +1327,7 @@ typedef enum {
  *   note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to
  *            read each contained frame header.  This is fast as most of the data is skipped,
  *            however it does mean that all frame data must be present and valid. */
-ZSTDLIB_API unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
+ZSTDLIB_STATIC_API unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
 
 /*! ZSTD_decompressBound() :
  *  `src` should point to the start of a series of ZSTD encoded and/or skippable frames
@@ -1296,13 +1342,13 @@ ZSTDLIB_API unsigned long long ZSTD_findDecompressedSize(const void* src, size_t
  *  note 3  : when the decompressed size field isn't available, the upper-bound for that frame is calculated by:
  *              upper-bound = # blocks * min(128 KB, Window_Size)
  */
-ZSTDLIB_API unsigned long long ZSTD_decompressBound(const void* src, size_t srcSize);
+ZSTDLIB_STATIC_API unsigned long long ZSTD_decompressBound(const void* src, size_t srcSize);
 
 /*! ZSTD_frameHeaderSize() :
  *  srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX.
  * @return : size of the Frame Header,
  *           or an error code (if srcSize is too small) */
-ZSTDLIB_API size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
+ZSTDLIB_STATIC_API size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
 
 typedef enum {
   ZSTD_sf_noBlockDelimiters = 0,         /* Representation of ZSTD_Sequence has no block delimiters, sequences only */
@@ -1325,7 +1371,7 @@ typedef enum {
  * @return : number of sequences generated
  */
 
-ZSTDLIB_API size_t ZSTD_generateSequences(ZSTD_CCtx* zc, ZSTD_Sequence* outSeqs,
+ZSTDLIB_STATIC_API size_t ZSTD_generateSequences(ZSTD_CCtx* zc, ZSTD_Sequence* outSeqs,
                                           size_t outSeqsSize, const void* src, size_t srcSize);
 
 /*! ZSTD_mergeBlockDelimiters() :
@@ -1339,7 +1385,7 @@ ZSTDLIB_API size_t ZSTD_generateSequences(ZSTD_CCtx* zc, ZSTD_Sequence* outSeqs,
  * setting of ZSTD_c_blockDelimiters as ZSTD_sf_noBlockDelimiters
  * @return : number of sequences left after merging
  */
-ZSTDLIB_API size_t ZSTD_mergeBlockDelimiters(ZSTD_Sequence* sequences, size_t seqsSize);
+ZSTDLIB_STATIC_API size_t ZSTD_mergeBlockDelimiters(ZSTD_Sequence* sequences, size_t seqsSize);
 
 /*! ZSTD_compressSequences() :
  * Compress an array of ZSTD_Sequence, generated from the original source buffer, into dst.
@@ -1369,7 +1415,7 @@ ZSTDLIB_API size_t ZSTD_mergeBlockDelimiters(ZSTD_Sequence* sequences, size_t se
  *         and cannot emit an RLE block that disagrees with the repcode history
  * @return : final compressed size or a ZSTD error.
  */
-ZSTDLIB_API size_t ZSTD_compressSequences(ZSTD_CCtx* const cctx, void* dst, size_t dstSize,
+ZSTDLIB_STATIC_API size_t ZSTD_compressSequences(ZSTD_CCtx* const cctx, void* dst, size_t dstSize,
                                   const ZSTD_Sequence* inSeqs, size_t inSeqsSize,
                                   const void* src, size_t srcSize);
 
@@ -1387,9 +1433,29 @@ ZSTDLIB_API size_t ZSTD_compressSequences(ZSTD_CCtx* const cctx, void* dst, size
  *
  * @return : number of bytes written or a ZSTD error.
  */
-ZSTDLIB_API size_t ZSTD_writeSkippableFrame(void* dst, size_t dstCapacity,
+ZSTDLIB_STATIC_API size_t ZSTD_writeSkippableFrame(void* dst, size_t dstCapacity,
                                             const void* src, size_t srcSize, unsigned magicVariant);
 
+/*! ZSTD_readSkippableFrame() :
+ * Retrieves a zstd skippable frame containing data given by src, and writes it to dst buffer.
+ *
+ * The parameter magicVariant will receive the magicVariant that was supplied when the frame was written,
+ * i.e. magicNumber - ZSTD_MAGIC_SKIPPABLE_START.  This can be NULL if the caller is not interested
+ * in the magicVariant.
+ *
+ * Returns an error if destination buffer is not large enough, or if the frame is not skippable.
+ *
+ * @return : number of bytes written or a ZSTD error.
+ */
+ZSTDLIB_API size_t ZSTD_readSkippableFrame(void* dst, size_t dstCapacity, unsigned* magicVariant,
+                                            const void* src, size_t srcSize);
+
+/*! ZSTD_isSkippableFrame() :
+ *  Tells if the content of `buffer` starts with a valid Frame Identifier for a skippable frame.
+ */
+ZSTDLIB_API unsigned ZSTD_isSkippableFrame(const void* buffer, size_t size);
+
+
 
 /* *************************************
 *  Memory management
@@ -1418,10 +1484,10 @@ ZSTDLIB_API size_t ZSTD_writeSkippableFrame(void* dst, size_t dstCapacity,
  *  Note 2 : only single-threaded compression is supported.
  *  ZSTD_estimateCCtxSize_usingCCtxParams() will return an error code if ZSTD_c_nbWorkers is >= 1.
  */
-ZSTDLIB_API size_t ZSTD_estimateCCtxSize(int compressionLevel);
-ZSTDLIB_API size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams);
-ZSTDLIB_API size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params);
-ZSTDLIB_API size_t ZSTD_estimateDCtxSize(void);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCCtxSize(int compressionLevel);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateDCtxSize(void);
 
 /*! ZSTD_estimateCStreamSize() :
  *  ZSTD_estimateCStreamSize() will provide a budget large enough for any compression level up to selected one.
@@ -1436,20 +1502,20 @@ ZSTDLIB_API size_t ZSTD_estimateDCtxSize(void);
  *  Note : if streaming is init with function ZSTD_init?Stream_usingDict(),
  *         an internal ?Dict will be created, which additional size is not estimated here.
  *         In this case, get total size by adding ZSTD_estimate?DictSize */
-ZSTDLIB_API size_t ZSTD_estimateCStreamSize(int compressionLevel);
-ZSTDLIB_API size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams);
-ZSTDLIB_API size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params);
-ZSTDLIB_API size_t ZSTD_estimateDStreamSize(size_t windowSize);
-ZSTDLIB_API size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCStreamSize(int compressionLevel);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateDStreamSize(size_t windowSize);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize);
 
 /*! ZSTD_estimate?DictSize() :
  *  ZSTD_estimateCDictSize() will bet that src size is relatively "small", and content is copied, like ZSTD_createCDict().
  *  ZSTD_estimateCDictSize_advanced() makes it possible to control compression parameters precisely, like ZSTD_createCDict_advanced().
  *  Note : dictionaries created by reference (`ZSTD_dlm_byRef`) are logically smaller.
  */
-ZSTDLIB_API size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel);
-ZSTDLIB_API size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod);
-ZSTDLIB_API size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod);
+ZSTDLIB_STATIC_API size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod);
 
 /*! ZSTD_initStatic*() :
  *  Initialize an object using a pre-allocated fixed-size buffer.
@@ -1472,20 +1538,20 @@ ZSTDLIB_API size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e
  *  Limitation 2 : static cctx currently not compatible with multi-threading.
  *  Limitation 3 : static dctx is incompatible with legacy support.
  */
-ZSTDLIB_API ZSTD_CCtx*    ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize);
-ZSTDLIB_API ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize);    /*< same as ZSTD_initStaticCCtx() */
+ZSTDLIB_STATIC_API ZSTD_CCtx*    ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize);
+ZSTDLIB_STATIC_API ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize);    /*< same as ZSTD_initStaticCCtx() */
 
-ZSTDLIB_API ZSTD_DCtx*    ZSTD_initStaticDCtx(void* workspace, size_t workspaceSize);
-ZSTDLIB_API ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize);    /*< same as ZSTD_initStaticDCtx() */
+ZSTDLIB_STATIC_API ZSTD_DCtx*    ZSTD_initStaticDCtx(void* workspace, size_t workspaceSize);
+ZSTDLIB_STATIC_API ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize);    /*< same as ZSTD_initStaticDCtx() */
 
-ZSTDLIB_API const ZSTD_CDict* ZSTD_initStaticCDict(
+ZSTDLIB_STATIC_API const ZSTD_CDict* ZSTD_initStaticCDict(
                                         void* workspace, size_t workspaceSize,
                                         const void* dict, size_t dictSize,
                                         ZSTD_dictLoadMethod_e dictLoadMethod,
                                         ZSTD_dictContentType_e dictContentType,
                                         ZSTD_compressionParameters cParams);
 
-ZSTDLIB_API const ZSTD_DDict* ZSTD_initStaticDDict(
+ZSTDLIB_STATIC_API const ZSTD_DDict* ZSTD_initStaticDDict(
                                         void* workspace, size_t workspaceSize,
                                         const void* dict, size_t dictSize,
                                         ZSTD_dictLoadMethod_e dictLoadMethod,
@@ -1504,44 +1570,44 @@ static
 __attribute__((__unused__))
 ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL };  /*< this constant defers to stdlib's functions */
 
-ZSTDLIB_API ZSTD_CCtx*    ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
-ZSTDLIB_API ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
-ZSTDLIB_API ZSTD_DCtx*    ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
-ZSTDLIB_API ZSTD_DStream* ZSTD_createDStream_advanced(ZSTD_customMem customMem);
+ZSTDLIB_STATIC_API ZSTD_CCtx*    ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
+ZSTDLIB_STATIC_API ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
+ZSTDLIB_STATIC_API ZSTD_DCtx*    ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
+ZSTDLIB_STATIC_API ZSTD_DStream* ZSTD_createDStream_advanced(ZSTD_customMem customMem);
 
-ZSTDLIB_API ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize,
+ZSTDLIB_STATIC_API ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize,
                                                   ZSTD_dictLoadMethod_e dictLoadMethod,
                                                   ZSTD_dictContentType_e dictContentType,
                                                   ZSTD_compressionParameters cParams,
                                                   ZSTD_customMem customMem);
 
-/* ! Thread pool :
- * These prototypes make it possible to share a thread pool among multiple compression contexts.
- * This can limit resources for applications with multiple threads where each one uses
- * a threaded compression mode (via ZSTD_c_nbWorkers parameter).
- * ZSTD_createThreadPool creates a new thread pool with a given number of threads.
- * Note that the lifetime of such pool must exist while being used.
- * ZSTD_CCtx_refThreadPool assigns a thread pool to a context (use NULL argument value
- * to use an internal thread pool).
- * ZSTD_freeThreadPool frees a thread pool, accepts NULL pointer.
+/*! Thread pool :
+ *  These prototypes make it possible to share a thread pool among multiple compression contexts.
+ *  This can limit resources for applications with multiple threads where each one uses
+ *  a threaded compression mode (via ZSTD_c_nbWorkers parameter).
+ *  ZSTD_createThreadPool creates a new thread pool with a given number of threads.
+ *  Note that the lifetime of such pool must exist while being used.
+ *  ZSTD_CCtx_refThreadPool assigns a thread pool to a context (use NULL argument value
+ *  to use an internal thread pool).
+ *  ZSTD_freeThreadPool frees a thread pool, accepts NULL pointer.
  */
 typedef struct POOL_ctx_s ZSTD_threadPool;
-ZSTDLIB_API ZSTD_threadPool* ZSTD_createThreadPool(size_t numThreads);
-ZSTDLIB_API void ZSTD_freeThreadPool (ZSTD_threadPool* pool);  /* accept NULL pointer */
-ZSTDLIB_API size_t ZSTD_CCtx_refThreadPool(ZSTD_CCtx* cctx, ZSTD_threadPool* pool);
+ZSTDLIB_STATIC_API ZSTD_threadPool* ZSTD_createThreadPool(size_t numThreads);
+ZSTDLIB_STATIC_API void ZSTD_freeThreadPool (ZSTD_threadPool* pool);  /* accept NULL pointer */
+ZSTDLIB_STATIC_API size_t ZSTD_CCtx_refThreadPool(ZSTD_CCtx* cctx, ZSTD_threadPool* pool);
 
 
 /*
  * This API is temporary and is expected to change or disap