From: Sean Purcell Date: Thu, 23 Feb 2017 21:45:04 +0000 (-0800) Subject: Dynamic loading version X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=34b9612e9f13c0210d276cac114f44293ced45c5;p=thirdparty%2Fzstd.git Dynamic loading version --- diff --git a/zstd_manual.html b/zstd_manual.html index 1badcbd79..2ba24cfb2 100644 --- a/zstd_manual.html +++ b/zstd_manual.html @@ -1,551 +1,21 @@ - + + - -zstd 1.1.2 Manual -

zstd 1.1.2 Manual

Introduction
Version
Simple API
Explicit memory management
Simple dictionary API
Fast dictionary API
Streaming
Streaming compression - HowTo
Streaming decompression - HowTo
START OF ADVANCED AND EXPERIMENTAL FUNCTIONS
Advanced types
Advanced compression functions
Advanced decompression functions
Advanced streaming functions
Buffer-less and synchronous inner streaming functions
Buffer-less streaming compression (synchronous mode)
Buffer-less streaming decompression (synchronous mode)
Block functions

Introduction

-  zstd, short for Zstandard, is a fast lossless compression algorithm, targeting real-time compression scenarios
-  at zlib-level and better compression ratios. The zstd compression library provides in-memory compression and
-  decompression functions. The library supports compression levels from 1 up to ZSTD_maxCLevel() which is 22.
-  Levels >= 20, labelled `--ultra`, should be used with caution, as they require more memory.
-  Compression can be done in:
-    - a single step (described as Simple API)
-    - a single step, reusing a context (described as Explicit memory management)
-    - unbounded multiple steps (described as Streaming compression)
-  The compression ratio achievable on small data can be highly improved using compression with a dictionary in:
-    - a single step (described as Simple dictionary API)
-    - a single step, reusing a dictionary (described as Fast dictionary API)
-
-  Advanced experimental functions can be accessed using #define ZSTD_STATIC_LINKING_ONLY before including zstd.h.
-  These APIs shall never be used with a dynamic library.
-  They are not "stable", their definition may change in the future. Only static linking is allowed.
-

- -

Version

- -

unsigned ZSTD_versionNumber(void);   /**< library version number; to be used when checking dll version */
-

Simple API

- -

size_t ZSTD_compress( void* dst, size_t dstCapacity,
-                            const void* src, size_t srcSize,
-                                  int compressionLevel);
-    Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
-    Hint : compression runs faster if `dstCapacity` >=  `ZSTD_compressBound(srcSize)`.
-    @return : compressed size written into `dst` (<= `dstCapacity),
-              or an error code if it fails (which can be tested using ZSTD_isError()). 
-

- -

size_t ZSTD_decompress( void* dst, size_t dstCapacity,
-                              const void* src, size_t compressedSize);
-    `compressedSize` : must be the _exact_ size of a single compressed frame.
-    `dstCapacity` is an upper bound of originalSize.
-    If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data.
-    @return : the number of bytes decompressed into `dst` (<= `dstCapacity`),
-              or an errorCode if it fails (which can be tested using ZSTD_isError()). 
-

- -

unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
-   'src' is the start of a zstd compressed frame.
-   @return : content size to be decompressed, as a 64-bits value _if known_, 0 otherwise.
-    note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
-             When `return==0`, data to decompress could be any size.
-             In which case, it's necessary to use streaming mode to decompress data.
-             Optionally, application can still use ZSTD_decompress() while relying on implied limits.
-             (For example, data may be necessarily cut into blocks <= 16 KB).
-    note 2 : decompressed size is always present when compression is done with ZSTD_compress()
-    note 3 : decompressed size can be very large (64-bits value),
-             potentially larger than what local system can handle as a single memory segment.
-             In which case, it's necessary to use streaming mode to decompress data.
-    note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
-             Always ensure result fits within application's authorized limits.
-             Each application can set its own limits.
-    note 5 : when `return==0`, if precise failure cause is needed, use ZSTD_getFrameParams() to know more. 
-

- -

Helper functions

int         ZSTD_maxCLevel(void);               /*!< maximum compression level available */
-size_t      ZSTD_compressBound(size_t srcSize); /*!< maximum compressed size in worst case scenario */
-unsigned    ZSTD_isError(size_t code);          /*!< tells if a `size_t` function result is an error code */
-const char* ZSTD_getErrorName(size_t code);     /*!< provides readable string from an error code */
-

Explicit memory management

- -

size_t ZSTD_compressCCtx(ZSTD_CCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize, int compressionLevel);
-    Same as ZSTD_compress(), requires an allocated ZSTD_CCtx (see ZSTD_createCCtx()). 
-

- -

Decompression context

typedef struct ZSTD_DCtx_s ZSTD_DCtx;
-ZSTD_DCtx* ZSTD_createDCtx(void);
-size_t     ZSTD_freeDCtx(ZSTD_DCtx* dctx);
-

size_t ZSTD_decompressDCtx(ZSTD_DCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
-   Same as ZSTD_decompress(), requires an allocated ZSTD_DCtx (see ZSTD_createDCtx()). 
-

- -

Simple dictionary API

- -

size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
-                                           void* dst, size_t dstCapacity,
-                                     const void* src, size_t srcSize,
-                                     const void* dict,size_t dictSize,
-                                           int compressionLevel);
-   Compression using a predefined Dictionary (see dictBuilder/zdict.h).
-   Note : This function loads the dictionary, resulting in significant startup delay.
-   Note : When `dict == NULL || dictSize < 8` no dictionary is used. 
-

- -

size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
-                                             void* dst, size_t dstCapacity,
-                                       const void* src, size_t srcSize,
-                                       const void* dict,size_t dictSize);
-   Decompression using a predefined Dictionary (see dictBuilder/zdict.h).
-   Dictionary must be identical to the one used during compression.
-   Note : This function loads the dictionary, resulting in significant startup delay.
-   Note : When `dict == NULL || dictSize < 8` no dictionary is used. 
-

- -

Fast dictionary API

- -

ZSTD_CDict* ZSTD_createCDict(const void* dict, size_t dictSize, int compressionLevel);
-   When compressing multiple messages / blocks with the same dictionary, it's recommended to load it just once.
-   ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
-   ZSTD_CDict can be created once and used by multiple threads concurrently, as its usage is read-only.
-   `dict` can be released after ZSTD_CDict creation. 
-

- -

size_t      ZSTD_freeCDict(ZSTD_CDict* CDict);
-   Function frees memory allocated by ZSTD_createCDict(). 
-

- -

size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
-                                            void* dst, size_t dstCapacity,
-                                      const void* src, size_t srcSize,
-                                      const ZSTD_CDict* cdict);
-   Compression using a digested Dictionary.
-   Faster startup than ZSTD_compress_usingDict(), recommended when same dictionary is used multiple times.
-   Note that compression level is decided during dictionary creation. 
-

- -

ZSTD_DDict* ZSTD_createDDict(const void* dict, size_t dictSize);
-   Create a digested dictionary, ready to start decompression operation without startup delay.
-   `dict` can be released after creation. 
-

- -

size_t      ZSTD_freeDDict(ZSTD_DDict* ddict);
-   Function frees memory allocated with ZSTD_createDDict() 
-

- -

size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
-                                              void* dst, size_t dstCapacity,
-                                        const void* src, size_t srcSize,
-                                        const ZSTD_DDict* ddict);
-   Decompression using a digested Dictionary.
-   Faster startup than ZSTD_decompress_usingDict(), recommended when same dictionary is used multiple times. 
-

- -

Streaming

- -

typedef struct ZSTD_inBuffer_s {
-  const void* src;    /**< start of input buffer */
-  size_t size;        /**< size of input buffer */
-  size_t pos;         /**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */
-} ZSTD_inBuffer;
-

typedef struct ZSTD_outBuffer_s {
-  void*  dst;         /**< start of output buffer */
-  size_t size;        /**< size of output buffer */
-  size_t pos;         /**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */
-} ZSTD_outBuffer;
-

Streaming compression - HowTo

-  A ZSTD_CStream object is required to track streaming operation.
-  Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources.
-  ZSTD_CStream objects can be reused multiple times on consecutive compression operations.
-  It is recommended to re-use ZSTD_CStream in situations where many streaming operations will be achieved consecutively,
-  since it will play nicer with system's memory, by re-using already allocated memory.
-  Use one separate ZSTD_CStream per thread for parallel execution.
-
-  Start a new compression by initializing ZSTD_CStream.
-  Use ZSTD_initCStream() to start a new compression operation.
-  Use ZSTD_initCStream_usingDict() or ZSTD_initCStream_usingCDict() for a compression which requires a dictionary (experimental section)
-
-  Use ZSTD_compressStream() repetitively to consume input stream.
-  The function will automatically update both `pos` fields.
-  Note that it may not consume the entire input, in which case `pos < size`,
-  and it's up to the caller to present again remaining data.
-  @return : a size hint, preferred nb of bytes to use as input for next function call
-            or an error code, which can be tested using ZSTD_isError().
-            Note 1 : it's just a hint, to help latency a little, any other value will work fine.
-            Note 2 : size hint is guaranteed to be <= ZSTD_CStreamInSize()
-
-  At any moment, it's possible to flush whatever data remains within internal buffer, using ZSTD_flushStream().
-  `output->pos` will be updated.
-  Note that some content might still be left within internal buffer if `output->size` is too small.
-  @return : nb of bytes still present within internal buffer (0 if it's empty)
-            or an error code, which can be tested using ZSTD_isError().
-
-  ZSTD_endStream() instructs to finish a frame.
-  It will perform a flush and write frame epilogue.
-  The epilogue is required for decoders to consider a frame completed.
-  Similar to ZSTD_flushStream(), it may not be able to flush the full content if `output->size` is too small.
-  In which case, call again ZSTD_endStream() to complete the flush.
-  @return : nb of bytes still present within internal buffer (0 if it's empty, hence compression completed)
-            or an error code, which can be tested using ZSTD_isError().
-
- 
-

- -

size_t ZSTD_CStreamInSize(void);    /**< recommended size for input buffer */
-

size_t ZSTD_CStreamOutSize(void);   /**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block in all circumstances. */
-

Streaming decompression - HowTo

-  A ZSTD_DStream object is required to track streaming operations.
-  Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources.
-  ZSTD_DStream objects can be re-used multiple times.
-
-  Use ZSTD_initDStream() to start a new decompression operation,
-   or ZSTD_initDStream_usingDict() if decompression requires a dictionary.
-   @return : recommended first input size
-
-  Use ZSTD_decompressStream() repetitively to consume your input.
-  The function will update both `pos` fields.
-  If `input.pos < input.size`, some input has not been consumed.
-  It's up to the caller to present again remaining data.
-  If `output.pos < output.size`, decoder has flushed everything it could.
-  @return : 0 when a frame is completely decoded and fully flushed,
-            an error code, which can be tested using ZSTD_isError(),
-            any other value > 0, which means there is still some decoding to do to complete current frame.
-            The return value is a suggested next input size (a hint to improve latency) that will never load more than the current frame.
- 
-

- -

size_t ZSTD_DStreamInSize(void);    /*!< recommended size for input buffer */
-

size_t ZSTD_DStreamOutSize(void);   /*!< recommended size for output buffer. Guarantee to successfully flush at least one complete block in all circumstances. */
-

START OF ADVANCED AND EXPERIMENTAL FUNCTIONS

 The definitions in this section are considered experimental.
- They should never be used with a dynamic library, as they may change in the future.
- They are provided for advanced usages.
- Use them only in association with static linking.
- 
-

- -

Advanced types

- -

typedef enum { ZSTD_fast, ZSTD_dfast, ZSTD_greedy, ZSTD_lazy, ZSTD_lazy2, ZSTD_btlazy2, ZSTD_btopt, ZSTD_btopt2 } ZSTD_strategy;   /* from faster to stronger */
-

typedef struct {
-    unsigned windowLog;      /**< largest match distance : larger == more compression, more memory needed during decompression */
-    unsigned chainLog;       /**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */
-    unsigned hashLog;        /**< dispatch table : larger == faster, more memory */
-    unsigned searchLog;      /**< nb of searches : larger == more compression, slower */
-    unsigned searchLength;   /**< match length searched : larger == faster decompression, sometimes less compression */
-    unsigned targetLength;   /**< acceptable match size for optimal parser (only) : larger == more compression, slower */
-    ZSTD_strategy strategy;
-} ZSTD_compressionParameters;
-

typedef struct {
-    unsigned contentSizeFlag; /**< 1: content size will be in frame header (if known). */
-    unsigned checksumFlag;    /**< 1: will generate a 22-bits checksum at end of frame, to be used for error detection by decompressor */
-    unsigned noDictIDFlag;    /**< 1: no dict ID will be saved into frame header (if dictionary compression) */
-} ZSTD_frameParameters;
-

typedef struct {
-    ZSTD_compressionParameters cParams;
-    ZSTD_frameParameters fParams;
-} ZSTD_parameters;
-

Custom memory allocation functions

typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
-typedef void  (*ZSTD_freeFunction) (void* opaque, void* address);
-typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
-

Advanced compression functions

- -

size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams); -

Gives the amount of memory allocated for a ZSTD_CCtx given a set of compression parameters. - `frameContentSize` is an optional parameter, provide `0` if unknown -

- -

ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem); -

Create a ZSTD compression context using external alloc and free functions -

- -

size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
-  Gives the amount of memory used by a given ZSTD_CCtx 
-

- -

ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize,
-                                                  ZSTD_parameters params, ZSTD_customMem customMem);
-  Create a ZSTD_CDict using external alloc and free, and customized compression parameters 
-

- -

size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
-  Gives the amount of memory used by a given ZSTD_sizeof_CDict 
-

- -

ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
-   @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
-   `estimatedSrcSize` value is optional, select 0 if not known 
-

- -

ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
-   same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`.
-   All fields of `ZSTD_frameParameters` are set to default (0) 
-

- -

size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
-   Ensure param values remain within authorized range 
-

- -

ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize); -

optimize params for a given `srcSize` and `dictSize`. - both values are optional, select `0` if unknown. -

- -

size_t ZSTD_compress_advanced (ZSTD_CCtx* ctx,
-                                           void* dst, size_t dstCapacity,
-                                     const void* src, size_t srcSize,
-                                     const void* dict,size_t dictSize,
-                                           ZSTD_parameters params);
-   Same as ZSTD_compress_usingDict(), with fine-tune control of each compression parameter 
-

- -

Advanced decompression functions

- -

unsigned ZSTD_isFrame(const void* buffer, size_t size);
-  Tells if the content of `buffer` starts with a valid Frame Identifier.
-  Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
-  Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
-  Note 3 : Skippable Frame Identifiers are considered valid. 
-

- -

size_t ZSTD_estimateDCtxSize(void);
-  Gives the potential amount of memory allocated to create a ZSTD_DCtx 
-

- -

ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem); -

Create a ZSTD decompression context using external alloc and free functions -

- -

size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
-  Gives the amount of memory used by a given ZSTD_DCtx 
-

- -

size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
-  Gives the amount of memory used by a given ZSTD_DDict 
-

- -

unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
-  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. 
-

- -

unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
-  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. 
-

- -

unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
-  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 :
-  - The frame does not require a dictionary to be decoded (most common case).
-  - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information.
-    Note : this use case also happens when using a non-conformant dictionary.
-  - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`).
-  - This is not a Zstandard frame.
-  When identifying the exact failure cause, it's possible to used ZSTD_getFrameParams(), which will provide a more precise error code. 
-

- -

Advanced streaming functions

- -

Advanced Streaming compression functions

ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
-size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize);   /**< pledgedSrcSize must be correct */
-size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel);
-size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
-                                             ZSTD_parameters params, unsigned long long pledgedSrcSize);  /**< pledgedSrcSize is optional and can be zero == unknown */
-size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict);  /**< note : cdict will just be referenced, and must outlive compression session */
-size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize);  /**< re-use compression parameters from previous init; skip dictionary loading stage; zcs must be init at least once before */
-size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
-

Advanced Streaming decompression functions

typedef enum { ZSTDdsp_maxWindowSize } ZSTD_DStreamParameter_e;
-ZSTD_DStream* ZSTD_createDStream_advanced(ZSTD_customMem customMem);
-size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize);
-size_t ZSTD_setDStreamParameter(ZSTD_DStream* zds, ZSTD_DStreamParameter_e paramType, unsigned paramValue);
-size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict);  /**< note : ddict will just be referenced, and must outlive decompression session */
-size_t ZSTD_resetDStream(ZSTD_DStream* zds);  /**< re-use decompression parameters from previous init; saves dictionary loading */
-size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
-

Buffer-less and synchronous inner streaming functions

-  This is an advanced API, giving full control over buffer management, for users which need direct control over memory.
-  But it's also a complex one, with many restrictions (documented below).
-  Prefer using normal streaming API for an easier experience
- 
-

- -

Buffer-less streaming compression (synchronous mode)

-  A ZSTD_CCtx object is required to track streaming operations.
-  Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource.
-  ZSTD_CCtx object can be re-used multiple times within successive compression operations.
-
-  Start by initializing a context.
-  Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression,
-  or ZSTD_compressBegin_advanced(), for finer parameter control.
-  It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
-
-  Then, consume your input using ZSTD_compressContinue().
-  There are some important considerations to keep in mind when using this advanced function :
-  - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffer only.
-  - Interface is synchronous : input is consumed entirely and produce 1+ (or more) compressed blocks.
-  - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
-    Worst case evaluation is provided by ZSTD_compressBound().
-    ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
-  - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
-    It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
-  - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
-    In which case, it will "discard" the relevant memory section from its history.
-
-  Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum.
-  It's possible to use a NULL,0 src content, in which case, it will write a final empty block to end the frame,
-  Without last block mark, frames will be considered unfinished (broken) by decoders.
-
-  You can then reuse `ZSTD_CCtx` (ZSTD_compressBegin()) to compress some new frame.
-

- -

Buffer-less streaming compression functions

size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
-size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
-size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize);
-size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize);
-size_t ZSTD_compressContinue(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
-size_t ZSTD_compressEnd(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
-

Buffer-less streaming decompression (synchronous mode)

-  A ZSTD_DCtx object is required to track streaming operations.
-  Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it.
-  A ZSTD_DCtx object can be re-used multiple times.
-
-  First typical operation is to retrieve frame parameters, using ZSTD_getFrameParams().
-  It fills a ZSTD_frameParams structure which provide important information to correctly decode the frame,
-  such as the minimum rolling buffer size to allocate to decompress data (`windowSize`),
-  and the dictionary ID used.
-  (Note : content size is optional, it may not be present. 0 means : content size unknown).
-  Note that these values could be wrong, either because of data malformation, or because an attacker is spoofing deliberate false information.
-  As a consequence, check that values remain within valid application range, especially `windowSize`, before allocation.
-  Each application can set its own limit, depending on local restrictions. For extended interoperability, it is recommended to support at least 8 MB.
-  Frame parameters are extracted from the beginning of the compressed frame.
-  Data fragment must be large enough to ensure successful decoding, typically `ZSTD_frameHeaderSize_max` bytes.
-  @result : 0 : successful decoding, the `ZSTD_frameParams` structure is correctly filled.
-           >0 : `srcSize` is too small, please provide at least @result bytes on next attempt.
-           errorCode, which can be tested using ZSTD_isError().
-
-  Start decompression, with ZSTD_decompressBegin() or ZSTD_decompressBegin_usingDict().
-  Alternatively, you can copy a prepared context, using ZSTD_copyDCtx().
-
-  Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
-  ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue().
-  ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail.
-
-  @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity).
-  It can be zero, which is not an error; it just means ZSTD_decompressContinue() has decoded some metadata item.
-  It can also be an error code, which can be tested with ZSTD_isError().
-
-  ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize`.
-  They should preferably be located contiguously, prior to current block.
-  Alternatively, a round buffer of sufficient size is also possible. Sufficient size is determined by frame parameters.
-  ZSTD_decompressContinue() is very sensitive to contiguity,
-  if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place,
-  or that previous contiguous segment is large enough to properly handle maximum back-reference.
-
-  A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero.
-  Context can then be reset to start a new decompression.
-
-  Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType().
-  This information is not required to properly decode a frame.
-
-  == Special case : skippable frames ==
-
-  Skippable frames allow integration of user-defined data into a flow of concatenated frames.
-  Skippable frames will be ignored (skipped) by a decompressor. The format of skippable frames is as follows :
-  a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F
-  b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits
-  c) Frame Content - any content (User Data) of length equal to Frame Size
-  For skippable frames ZSTD_decompressContinue() always returns 0.
-  For skippable frames ZSTD_getFrameParams() returns fparamsPtr->windowLog==0 what means that a frame is skippable.
-  It also returns Frame Size as fparamsPtr->frameContentSize.
-

- -

typedef struct {
-    unsigned long long frameContentSize;
-    unsigned windowSize;
-    unsigned dictID;
-    unsigned checksumFlag;
-} ZSTD_frameParams;
-

Buffer-less streaming decompression functions

size_t ZSTD_getFrameParams(ZSTD_frameParams* fparamsPtr, const void* src, size_t srcSize);   /**< doesn't consume input, see details below */
-size_t ZSTD_decompressBegin(ZSTD_DCtx* dctx);
-size_t ZSTD_decompressBegin_usingDict(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
-void   ZSTD_copyDCtx(ZSTD_DCtx* dctx, const ZSTD_DCtx* preparedDCtx);
-size_t ZSTD_nextSrcSizeToDecompress(ZSTD_DCtx* dctx);
-size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
-typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
-ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx);
-

Block functions

-    Block functions produce and decode raw zstd blocks, without frame metadata.
-    Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes).
-    User will have to take in charge required information to regenerate data, such as compressed and content sizes.
-
-    A few rules to respect :
-    - Compressing and decompressing require a context structure
-      + Use ZSTD_createCCtx() and ZSTD_createDCtx()
-    - It is necessary to init context before starting
-      + compression : ZSTD_compressBegin()
-      + decompression : ZSTD_decompressBegin()
-      + variants _usingDict() are also allowed
-      + copyCCtx() and copyDCtx() work too
-    - Block size is limited, it must be <= ZSTD_getBlockSizeMax()
-      + If you need to compress more, cut data into multiple blocks
-      + Consider using the regular ZSTD_compress() instead, as frame metadata costs become negligible when source size is large.
-    - When a block is considered not compressible enough, ZSTD_compressBlock() result will be zero.
-      In which case, nothing is produced into `dst`.
-      + User must test for such outcome and deal directly with uncompressed data
-      + ZSTD_decompressBlock() doesn't accept uncompressed data as input !!!
-      + In case of multiple successive blocks, decoder must be informed of uncompressed block existence to follow proper history.
-        Use ZSTD_insertBlock() in such a case.
-

- -

Raw zstd block functions

size_t ZSTD_getBlockSizeMax(ZSTD_CCtx* cctx);
-size_t ZSTD_compressBlock  (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
-size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
-size_t ZSTD_insertBlock(ZSTD_DCtx* dctx, const void* blockStart, size_t blockSize);  /**< insert block into `dctx` history. Useful for uncompressed blocks */
-

- +