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-<h1>zstd 1.1.2 Manual</h1>
-<hr>
-<a name="Contents"></a><h2>Contents</h2>
-<ol>
-<li><a href="#Chapter1">Introduction</a></li>
-<li><a href="#Chapter2">Version</a></li>
-<li><a href="#Chapter3">Simple API</a></li>
-<li><a href="#Chapter4">Explicit memory management</a></li>
-<li><a href="#Chapter5">Simple dictionary API</a></li>
-<li><a href="#Chapter6">Fast dictionary API</a></li>
-<li><a href="#Chapter7">Streaming</a></li>
-<li><a href="#Chapter8">Streaming compression - HowTo</a></li>
-<li><a href="#Chapter9">Streaming decompression - HowTo</a></li>
-<li><a href="#Chapter10">START OF ADVANCED AND EXPERIMENTAL FUNCTIONS</a></li>
-<li><a href="#Chapter11">Advanced types</a></li>
-<li><a href="#Chapter12">Advanced compression functions</a></li>
-<li><a href="#Chapter13">Advanced decompression functions</a></li>
-<li><a href="#Chapter14">Advanced streaming functions</a></li>
-<li><a href="#Chapter15">Buffer-less and synchronous inner streaming functions</a></li>
-<li><a href="#Chapter16">Buffer-less streaming compression (synchronous mode)</a></li>
-<li><a href="#Chapter17">Buffer-less streaming decompression (synchronous mode)</a></li>
-<li><a href="#Chapter18">Block functions</a></li>
-</ol>
-<hr>
-<a name="Chapter1"></a><h2>Introduction</h2><pre>
- 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.
-<BR></pre>
-
-<a name="Chapter2"></a><h2>Version</h2><pre></pre>
-
-<pre><b>unsigned ZSTD_versionNumber(void); </b>/**< library version number; to be used when checking dll version */<b>
-</b></pre><BR>
-<a name="Chapter3"></a><h2>Simple API</h2><pre></pre>
-
-<pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- int compressionLevel);
-</b><p> 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()).
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity,
- const void* src, size_t compressedSize);
-</b><p> `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()).
-</p></pre><BR>
-
-<pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
-</b><p> '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.
-</p></pre><BR>
-
-<h3>Helper functions</h3><pre><b>int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b>
-size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case scenario */<b>
-unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b>
-const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b>
-</b></pre><BR>
-<a name="Chapter4"></a><h2>Explicit memory management</h2><pre></pre>
-
-<pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize, int compressionLevel);
-</b><p> Same as ZSTD_compress(), requires an allocated ZSTD_CCtx (see ZSTD_createCCtx()).
-</p></pre><BR>
-
-<h3>Decompression context</h3><pre><b>typedef struct ZSTD_DCtx_s ZSTD_DCtx;
-ZSTD_DCtx* ZSTD_createDCtx(void);
-size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
-</b></pre><BR>
-<pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
-</b><p> Same as ZSTD_decompress(), requires an allocated ZSTD_DCtx (see ZSTD_createDCtx()).
-</p></pre><BR>
-
-<a name="Chapter5"></a><h2>Simple dictionary API</h2><pre></pre>
-
-<pre><b>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);
-</b><p> 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.
-</p></pre><BR>
-
-<pre><b>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);
-</b><p> 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.
-</p></pre><BR>
-
-<a name="Chapter6"></a><h2>Fast dictionary API</h2><pre></pre>
-
-<pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dict, size_t dictSize, int compressionLevel);
-</b><p> 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.
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict);
-</b><p> Function frees memory allocated by ZSTD_createCDict().
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const ZSTD_CDict* cdict);
-</b><p> 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.
-</p></pre><BR>
-
-<pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dict, size_t dictSize);
-</b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
- `dict` can be released after creation.
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict);
-</b><p> Function frees memory allocated with ZSTD_createDDict()
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const ZSTD_DDict* ddict);
-</b><p> Decompression using a digested Dictionary.
- Faster startup than ZSTD_decompress_usingDict(), recommended when same dictionary is used multiple times.
-</p></pre><BR>
-
-<a name="Chapter7"></a><h2>Streaming</h2><pre></pre>
-
-<pre><b>typedef struct ZSTD_inBuffer_s {
- const void* src; </b>/**< start of input buffer */<b>
- size_t size; </b>/**< size of input buffer */<b>
- size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
-} ZSTD_inBuffer;
-</b></pre><BR>
-<pre><b>typedef struct ZSTD_outBuffer_s {
- void* dst; </b>/**< start of output buffer */<b>
- size_t size; </b>/**< size of output buffer */<b>
- size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
-} ZSTD_outBuffer;
-</b></pre><BR>
-<a name="Chapter8"></a><h2>Streaming compression - HowTo</h2><pre>
- 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().
-
-
-<BR></pre>
-
-<pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b>
-</b></pre><BR>
-<pre><b>size_t ZSTD_CStreamOutSize(void); </b>/**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block in all circumstances. */<b>
-</b></pre><BR>
-<a name="Chapter9"></a><h2>Streaming decompression - HowTo</h2><pre>
- 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.
-
-<BR></pre>
-
-<pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b>
-</b></pre><BR>
-<pre><b>size_t ZSTD_DStreamOutSize(void); </b>/*!< recommended size for output buffer. Guarantee to successfully flush at least one complete block in all circumstances. */<b>
-</b></pre><BR>
-<a name="Chapter10"></a><h2>START OF ADVANCED AND EXPERIMENTAL FUNCTIONS</h2><pre> 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.
-
-<BR></pre>
-
-<a name="Chapter11"></a><h2>Advanced types</h2><pre></pre>
-
-<pre><b>typedef enum { ZSTD_fast, ZSTD_dfast, ZSTD_greedy, ZSTD_lazy, ZSTD_lazy2, ZSTD_btlazy2, ZSTD_btopt, ZSTD_btopt2 } ZSTD_strategy; </b>/* from faster to stronger */<b>
-</b></pre><BR>
-<pre><b>typedef struct {
- unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b>
- unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b>
- unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b>
- unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b>
- unsigned searchLength; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b>
- unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b>
- ZSTD_strategy strategy;
-} ZSTD_compressionParameters;
-</b></pre><BR>
-<pre><b>typedef struct {
- unsigned contentSizeFlag; </b>/**< 1: content size will be in frame header (if known). */<b>
- unsigned checksumFlag; </b>/**< 1: will generate a 22-bits checksum at end of frame, to be used for error detection by decompressor */<b>
- unsigned noDictIDFlag; </b>/**< 1: no dict ID will be saved into frame header (if dictionary compression) */<b>
-} ZSTD_frameParameters;
-</b></pre><BR>
-<pre><b>typedef struct {
- ZSTD_compressionParameters cParams;
- ZSTD_frameParameters fParams;
-} ZSTD_parameters;
-</b></pre><BR>
-<h3>Custom memory allocation functions</h3><pre><b>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;
-</b></pre><BR>
-<a name="Chapter12"></a><h2>Advanced compression functions</h2><pre></pre>
-
-<pre><b>size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
-</b><p> 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
-</p></pre><BR>
-
-<pre><b>ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
-</b><p> Create a ZSTD compression context using external alloc and free functions
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
-</b><p> Gives the amount of memory used by a given ZSTD_CCtx
-</p></pre><BR>
-
-<pre><b>ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize,
- ZSTD_parameters params, ZSTD_customMem customMem);
-</b><p> Create a ZSTD_CDict using external alloc and free, and customized compression parameters
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
-</b><p> Gives the amount of memory used by a given ZSTD_sizeof_CDict
-</p></pre><BR>
-
-<pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
-</b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
- `estimatedSrcSize` value is optional, select 0 if not known
-</p></pre><BR>
-
-<pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
-</b><p> 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)
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
-</b><p> Ensure param values remain within authorized range
-</p></pre><BR>
-
-<pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize);
-</b><p> optimize params for a given `srcSize` and `dictSize`.
- both values are optional, select `0` if unknown.
-</p></pre><BR>
-
-<pre><b>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);
-</b><p> Same as ZSTD_compress_usingDict(), with fine-tune control of each compression parameter
-</p></pre><BR>
-
-<a name="Chapter13"></a><h2>Advanced decompression functions</h2><pre></pre>
-
-<pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size);
-</b><p> 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.
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_estimateDCtxSize(void);
-</b><p> Gives the potential amount of memory allocated to create a ZSTD_DCtx
-</p></pre><BR>
-
-<pre><b>ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
-</b><p> Create a ZSTD decompression context using external alloc and free functions
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
-</b><p> Gives the amount of memory used by a given ZSTD_DCtx
-</p></pre><BR>
-
-<pre><b>size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
-</b><p> Gives the amount of memory used by a given ZSTD_DDict
-</p></pre><BR>
-
-<pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
-</b><p> 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.
-</p></pre><BR>
-
-<pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
-</b><p> 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.
-</p></pre><BR>
-
-<pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
-</b><p> 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.
-</p></pre><BR>
-
-<a name="Chapter14"></a><h2>Advanced streaming functions</h2><pre></pre>
-
-<h3>Advanced Streaming compression functions</h3><pre><b>ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
-size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize must be correct */<b>
-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); </b>/**< pledgedSrcSize is optional and can be zero == unknown */<b>
-size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict); </b>/**< note : cdict will just be referenced, and must outlive compression session */<b>
-size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize); </b>/**< re-use compression parameters from previous init; skip dictionary loading stage; zcs must be init at least once before */<b>
-size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
-</b></pre><BR>
-<h3>Advanced Streaming decompression functions</h3><pre><b>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); </b>/**< note : ddict will just be referenced, and must outlive decompression session */<b>
-size_t ZSTD_resetDStream(ZSTD_DStream* zds); </b>/**< re-use decompression parameters from previous init; saves dictionary loading */<b>
-size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
-</b></pre><BR>
-<a name="Chapter15"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre>
- 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
-
-<BR></pre>
-
-<a name="Chapter16"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre>
- 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.
-<BR></pre>
-
-<h3>Buffer-less streaming compression functions</h3><pre><b>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);
-</b></pre><BR>
-<a name="Chapter17"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre>
- 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.
-<BR></pre>
-
-<pre><b>typedef struct {
- unsigned long long frameContentSize;
- unsigned windowSize;
- unsigned dictID;
- unsigned checksumFlag;
-} ZSTD_frameParams;
-</b></pre><BR>
-<h3>Buffer-less streaming decompression functions</h3><pre><b>size_t ZSTD_getFrameParams(ZSTD_frameParams* fparamsPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input, see details below */<b>
-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);
-</b></pre><BR>
-<a name="Chapter18"></a><h2>Block functions</h2><pre>
- 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.
-<BR></pre>
-
-<h3>Raw zstd block functions</h3><pre><b>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); </b>/**< insert block into `dctx` history. Useful for uncompressed blocks */<b>
-</b></pre><BR>
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