Contains the compressed frame size and an upper-bound for the decompressed frame size.
Note: before using compressedSize, check for errors using ZSTD_isError().
similarly, before using decompressedBound, check for errors using:
decompressedBound != ZSTD_CONTENTSIZE_ERROR
If set: If the previous table can encode the input, always reuse the previous table.
If unset: If the previous table can encode the input, reuse the previous table if it results in a smaller output.
If set: Sample the input and check if the sample is uncompressible, if it is then don’t attempt to compress.
If unset: Always histogram the entire input.
< Automatically determine the compression mode based on the compression level.
Negative compression levels will be uncompressed, and positive compression
levels will be compressed.
FSE_NCountWriteBound():
Provides the maximum possible size of an FSE normalized table, given ‘maxSymbolValue’ and ‘tableLog’.
Typically useful for allocation purpose.
FSE_buildCTable():
Builds ct, which must be already allocated, using FSE_createCTable().
@return : 0, or an errorCode, which can be tested using FSE_isError()
FSE_compress_usingCTable():
Compress src using ct into dst which must be already allocated.
@return : size of compressed data (<= dstCapacity),
or 0 if compressed data could not fit into dst,
or an errorCode, which can be tested using FSE_isError()
FSE_normalizeCount():
normalize counts so that sum(count[]) == Power_of_2 (2^tableLog)
‘normalizedCounter’ is a table of short, of minimum size (maxSymbolValue+1).
useLowProbCount is a boolean parameter which trades off compressed size for
faster header decoding. When it is set to 1, the compressed data will be slightly
smaller. And when it is set to 0, FSE_readNCount() and FSE_buildDTable() will be
faster. If you are compressing a small amount of data (< 2 KB) then useLowProbCount=0
is a good default, since header deserialization makes a big speed difference.
Otherwise, useLowProbCount=1 is a good default, since the speed difference is small.
@return : tableLog,
or an errorCode, which can be tested using FSE_isError()
FSE_optimalTableLog():
dynamically downsize ‘tableLog’ when conditions are met.
It saves CPU time, by using smaller tables, while preserving or even improving compression ratio.
@return : recommended tableLog (necessarily <= ‘maxTableLog’)
FSE_readNCount():
Read compactly saved ‘normalizedCounter’ from ‘rBuffer’.
@return : size read from ‘rBuffer’,
or an errorCode, which can be tested using FSE_isError().
maxSymbolValuePtr[0] and tableLogPtr[0] will also be updated with their respective values
FSE_writeNCount():
Compactly save ‘normalizedCounter’ into ‘buffer’.
@return : size of the compressed table,
or an errorCode, which can be tested using FSE_isError().
HUF_compress1X_repeat() :
Same as HUF_compress1X_wksp(), but considers using hufTable if *repeat != HUF_repeat_none.
If it uses hufTable it does not modify hufTable or repeat.
If it doesn’t, it sets *repeat = HUF_repeat_none, and it sets hufTable to the table used.
If preferRepeat then the old table will always be used if valid.
If suspectUncompressible then some sampling checks will be run to potentially skip huffman coding
HUF_compress4X_repeat() :
Same as HUF_compress4X_wksp(), but considers using hufTable if *repeat != HUF_repeat_none.
If it uses hufTable it does not modify hufTable or repeat.
If it doesn’t, it sets *repeat = HUF_repeat_none, and it sets hufTable to the table used.
If preferRepeat then the old table will always be used if valid.
If suspectUncompressible then some sampling checks will be run to potentially skip huffman coding
HUF_getNbBitsFromCTable() :
Read nbBits from CTable symbolTable, for symbol symbolValue presumed <= HUF_SYMBOLVALUE_MAX
Note 1 : is not inlined, as HUF_CElt definition is private
HUF_readStats() :
Read compact Huffman tree, saved by HUF_writeCTable().
huffWeight is destination buffer.
@return : size read from src , or an error Code .
Note : Needed by HUF_readCTable() and HUF_readDTableXn() .
HUF_selectDecoder() :
Tells which decoder is likely to decode faster,
based on a set of pre-computed metrics.
@return : 0==HUF_decompress4X1, 1==HUF_decompress4X2 .
Assumption : 0 < dstSize <= 128 KB
ZSTD_CCtxParams_getParameter() :
Similar to ZSTD_CCtx_getParameter.
Get the requested value of one compression parameter, selected by enum ZSTD_cParameter.
@result : 0, or an error code (which can be tested with ZSTD_isError()).
ZSTD_CCtxParams_init() :
Initializes the compression parameters of cctxParams according to
compression level. All other parameters are reset to their default values.
ZSTD_CCtxParams_init_advanced() :
Initializes the compression and frame parameters of cctxParams according to
params. All other parameters are reset to their default values.
ZSTD_CCtxParams_setParameter() : Requires v1.4.0+
Similar to ZSTD_CCtx_setParameter.
Set one compression parameter, selected by enum ZSTD_cParameter.
Parameters must be applied to a ZSTD_CCtx using
ZSTD_CCtx_setParametersUsingCCtxParams().
@result : a code representing success or failure (which can be tested with
ZSTD_isError()).
ZSTD_CCtx_getParameter() :
Get the requested compression parameter value, selected by enum ZSTD_cParameter,
and store it into int* value.
@return : 0, or an error code (which can be tested with ZSTD_isError()).
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()).
Special: Loading a NULL (or 0-size) dictionary invalidates previous dictionary,
meaning “return to no-dictionary mode”.
Note 1 : Dictionary is sticky, it will be used for all future compressed frames,
until parameters are reset, a new dictionary is loaded, or the dictionary
is explicitly invalidated by loading a NULL dictionary.
Note 2 : Loading a dictionary involves building tables.
It’s also a CPU consuming operation, with non-negligible impact on latency.
Tables are dependent on compression parameters, and for this reason,
compression parameters can no longer be changed after loading a dictionary.
Note 3 :dict content will be copied internally.
Use experimental ZSTD_CCtx_loadDictionary_byReference() to reference content instead.
In such a case, dictionary buffer must outlive its users.
Note 4 : Use ZSTD_CCtx_loadDictionary_advanced()
to precisely select how dictionary content must be interpreted.
Note 5 : This method does not benefit from LDM (long distance mode).
If you want to employ LDM on some large dictionary content,
prefer employing ZSTD_CCtx_refPrefix() described below.
ZSTD_CCtx_loadDictionary_advanced() :
Same as ZSTD_CCtx_loadDictionary(), but gives finer control over
how to load the dictionary (by copy ? by reference ?)
and how to interpret it (automatic ? force raw mode ? full mode only ?)
ZSTD_CCtx_loadDictionary_byReference() :
Same as ZSTD_CCtx_loadDictionary(), but dictionary content is referenced, instead of being copied into CCtx.
It saves some memory, but also requires that dict outlives its usage within cctx
ZSTD_CCtx_refCDict() : Requires v1.4.0+
Reference a prepared dictionary, to be used for all future compressed frames.
Note that compression parameters are enforced from within CDict,
and supersede any compression parameter previously set within CCtx.
The parameters ignored are labelled as “superseded-by-cdict” in the ZSTD_cParameter enum docs.
The ignored parameters will be used again if the CCtx is returned to no-dictionary mode.
The dictionary will remain valid for future compressed frames using same CCtx.
@result : 0, or an error code (which can be tested with ZSTD_isError()).
Special : Referencing a NULL CDict means “return to no-dictionary mode”.
Note 1 : Currently, only one dictionary can be managed.
Referencing a new dictionary effectively “discards” any previous one.
Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx.
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.
Compressing with a prefix is similar in outcome as performing a diff and compressing it,
but performs much faster, especially during decompression (compression speed is tunable with compression level).
This method is compatible with LDM (long distance mode).
@result : 0, or an error code (which can be tested with ZSTD_isError()).
Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary
Note 1 : Prefix buffer is referenced. It must outlive compression.
Its content must remain unmodified during compression.
Note 2 : If the intention is to diff some large src data blob with some prior version of itself,
ensure that the window size is large enough to contain the entire source.
See ZSTD_c_windowLog.
Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters.
It’s a CPU consuming operation, with non-negligible impact on latency.
If there is a need to use the same prefix multiple times, consider loadDictionary instead.
Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dct_rawContent).
Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation.
ZSTD_CCtx_refPrefix_advanced() :
Same as ZSTD_CCtx_refPrefix(), but gives finer control over
how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
ZSTD_CCtx_setCParams() :
Set all parameters provided within @p cparams into the working @p cctx.
Note : if modifying parameters during compression (MT mode only),
note that changes to the .windowLog parameter will be ignored.
@return 0 on success, or an error code (can be checked with ZSTD_isError()).
On failure, no parameters are updated.
ZSTD_CCtx_setFParams() :
Set all parameters provided within @p fparams into the working @p cctx.
@return 0 on success, or an error code (can be checked with ZSTD_isError()).
ZSTD_CCtx_setParameter() :
Set one compression parameter, selected by enum ZSTD_cParameter.
All parameters have valid bounds. Bounds can be queried using ZSTD_cParam_getBounds().
Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
Setting a parameter is generally only possible during frame initialization (before starting compression).
Exception : when using multi-threading mode (nbWorkers >= 1),
the following parameters can be updated during compression (within same frame):
=> compressionLevel, hashLog, chainLog, searchLog, minMatch, targetLength and strategy.
new parameters will be active for next job only (after a flush()).
@return : an error code (which can be tested using ZSTD_isError()).
ZSTD_CCtx_setParametersUsingCCtxParams() :
Apply a set of ZSTD_CCtx_params to the compression context.
This can be done even after compression is started,
if nbWorkers==0, this will have no impact until a new compression is started.
if nbWorkers>=1, new parameters will be picked up at next job,
with a few restrictions (windowLog, pledgedSrcSize, nbWorkers, jobSize, and overlapLog are not updated).
ZSTD_CCtx_setParams() :
Set all parameters provided within @p params into the working @p cctx.
@return 0 on success, or an error code (can be checked with ZSTD_isError()).
ZSTD_CCtx_setPledgedSrcSize() :
Total input data size to be compressed as a single frame.
Value will be written in frame header, unless if explicitly forbidden using ZSTD_c_contentSizeFlag.
This value will also be controlled at end of frame, and trigger an error if not respected.
@result : 0, or an error code (which can be tested with ZSTD_isError()).
Note 1 : pledgedSrcSize==0 actually means zero, aka an empty frame.
In order to mean “unknown content size”, pass constant ZSTD_CONTENTSIZE_UNKNOWN.
ZSTD_CONTENTSIZE_UNKNOWN is default value for any new frame.
Note 2 : pledgedSrcSize is only valid once, for the next frame.
It’s discarded at the end of the frame, and replaced by ZSTD_CONTENTSIZE_UNKNOWN.
Note 3 : Whenever all input data is provided and consumed in a single round,
for example with ZSTD_compress2(),
or invoking immediately ZSTD_compressStream2(,,,ZSTD_e_end),
this value is automatically overridden by srcSize instead.
ZSTD_DCtx_getParameter() :
Get the requested decompression parameter value, selected by enum ZSTD_dParameter,
and store it into int* value.
@return : 0, or an error code (which can be tested with ZSTD_isError()).
ZSTD_DCtx_loadDictionary() : Requires v1.4.0+
Create an internal DDict from dict buffer, to be used to decompress all future frames.
The dictionary remains valid for all future frames, until explicitly invalidated, or
a new dictionary is loaded.
@result : 0, or an error code (which can be tested with ZSTD_isError()).
Special : Adding a NULL (or 0-size) dictionary invalidates any previous dictionary,
meaning “return to no-dictionary mode”.
Note 1 : Loading a dictionary involves building tables,
which has a non-negligible impact on CPU usage and latency.
It’s recommended to “load once, use many times”, to amortize the cost
Note 2 :dict content will be copied internally, so dict can be released after loading.
Use ZSTD_DCtx_loadDictionary_byReference() to reference dictionary content instead.
Note 3 : Use ZSTD_DCtx_loadDictionary_advanced() to take control of
how dictionary content is loaded and interpreted.
ZSTD_DCtx_loadDictionary_advanced() :
Same as ZSTD_DCtx_loadDictionary(),
but gives direct control over
how to load the dictionary (by copy ? by reference ?)
and how to interpret it (automatic ? force raw mode ? full mode only ?).
ZSTD_DCtx_loadDictionary_byReference() :
Same as ZSTD_DCtx_loadDictionary(),
but references dict content instead of copying it into dctx.
This saves memory if dict remains around.,
However, it’s imperative that dict remains accessible (and unmodified) while being used, so it must outlive decompression.
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.
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.
Prefix is only used once. Reference is discarded at end of frame.
End of frame is reached when ZSTD_decompressStream() returns 0.
@result : 0, or an error code (which can be tested with ZSTD_isError()).
Note 1 : Adding any prefix (including NULL) invalidates any previously set prefix or dictionary
Note 2 : Prefix buffer is referenced. It must outlive decompression.
Prefix buffer must remain unmodified up to the end of frame,
reached when ZSTD_decompressStream() returns 0.
Note 3 : By default, the prefix is treated as raw content (ZSTD_dct_rawContent).
Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode (Experimental section)
Note 4 : Referencing a raw content prefix has almost no cpu nor memory cost.
A full dictionary is more costly, as it requires building tables.
ZSTD_DCtx_refPrefix_advanced() :
Same as ZSTD_DCtx_refPrefix(), but gives finer control over
how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
ZSTD_DCtx_reset() :
Return a DCtx to clean state.
Session and parameters can be reset jointly or separately.
Parameters can only be reset when no active frame is being decompressed.
@return : 0, or an error code, which can be tested with ZSTD_isError()
ZSTD_DCtx_setFormat() :
This function is REDUNDANT. Prefer ZSTD_DCtx_setParameter().
Instruct the decoder context about what kind of data to decode next.
This instruction is mandatory to decode data without a fully-formed header,
such ZSTD_f_zstd1_magicless for example.
@return : 0, or an error code (which can be tested using ZSTD_isError()).
ZSTD_DCtx_setMaxWindowSize() :
Refuses allocating internal buffers for frames requiring a window size larger than provided limit.
This protects a decoder context from reserving too much memory for itself (potential attack scenario).
This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode.
By default, a decompression context accepts all window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT)
@return : 0, or an error code (which can be tested using ZSTD_isError()).
ZSTD_DCtx_setParameter() :
Set one compression parameter, selected by enum ZSTD_dParameter.
All parameters have valid bounds. Bounds can be queried using ZSTD_dParam_getBounds().
Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
Setting a parameter is only possible during frame initialization (before starting decompression).
@return : 0, or an error code (which can be tested using ZSTD_isError()).
ZSTD_adjustCParams() :
optimize params for a given srcSize and dictSize.
srcSize can be unknown, in which case use ZSTD_CONTENTSIZE_UNKNOWN.
dictSize must be 0 when there is no dictionary.
cPar can be invalid : all parameters will be clamped within valid range in the @return struct.
This function never fails (wide contract)
ZSTD_cParam_getBounds() :
All parameters must belong to an interval with lower and upper bounds,
otherwise they will either trigger an error or be automatically clamped.
@return : a structure, ZSTD_bounds, which contains
- an error status field, which must be tested using ZSTD_isError()
- lower and upper bounds, both inclusive
ZSTD_checkContinuity() :
check if next dst follows previous position, where decompression ended.
If yes, do nothing (continue on current segment).
If not, classify previous segment as “external dictionary”, and start a new segment.
This function cannot fail.
Simple API
/
/*! ZSTD_compress() :
Compresses src content as a single zstd compressed frame into already allocated dst.
NOTE: Providing dstCapacity >= ZSTD_compressBound(srcSize) guarantees that zstd will have
enough space to successfully compress the data.
@return : compressed size written into dst (<= `dstCapacity),
or an error code if it fails (which can be tested using ZSTD_isError()).
ZSTD_compress2() :
Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API.
ZSTD_compress2() always starts a new frame.
Should cctx hold data from a previously unfinished frame, everything about it is forgotten.
ZSTD_compressCCtx() :
Same as ZSTD_compress(), using an explicit ZSTD_CCtx.
Important : in order to behave similarly to ZSTD_compress(),
this function compresses at requested compression level,
ignoring any other parameter .
If any advanced parameter was set using the advanced API,
they will all be reset. Only compressionLevel remains.
ZSTD_compressSequences() :
Compress an array of ZSTD_Sequence, associated with @src buffer, into dst.
@src contains the entire input (not just the literals).
If @srcSize > sum(sequence.length), the remaining bytes are considered all literals
If a dictionary is included, then the cctx should reference the dict. (see: ZSTD_CCtx_refCDict(), ZSTD_CCtx_loadDictionary(), etc.)
The entire source is compressed into a single frame.
Alternative for ZSTD_compressStream2(zcs, output, input, ZSTD_e_continue).
NOTE: The return value is different. ZSTD_compressStream() returns a hint for
the next read size (if non-zero and not an error). ZSTD_compressStream2()
returns the minimum nb of bytes left to flush (if non-zero and not an error).
ZSTD_compressStream2_simpleArgs() :
Same as ZSTD_compressStream2(),
but using only integral types as arguments.
This variant might be helpful for binders from dynamic languages
which have troubles handling structures containing memory pointers.
ZSTD_compress_advanced() :
Note : this function is now DEPRECATED.
It can be replaced by ZSTD_compress2(), in combination with ZSTD_CCtx_setParameter() and other parameter setters.
This prototype will generate compilation warnings.
ZSTD_compress_usingCDict() :
Compression using a digested Dictionary.
Recommended when same dictionary is used multiple times.
Note : compression level is decided at dictionary creation time,
and frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no)
ZSTD_compress_usingCDict_advanced() :
Note : this function is now DEPRECATED.
It can be replaced by ZSTD_compress2(), in combination with ZSTD_CCtx_loadDictionary() and other parameter setters.
This prototype will generate compilation warnings.
Simple dictionary API
/
/*! 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 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.
ZSTD_createCDict() :
When compressing multiple messages or blocks using the same dictionary,
it’s recommended to digest the dictionary only once, since it’s a costly operation.
ZSTD_createCDict() will create a state from digesting a dictionary.
The resulting state can be used for future compression operations with very limited startup cost.
ZSTD_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
@dictBuffer can be released after ZSTD_CDict creation, because its content is copied within CDict.
Note 1 : Consider experimental function ZSTD_createCDict_byReference() if you prefer to not duplicate @dictBuffer content.
Note 2 : A ZSTD_CDict can be created from an empty @dictBuffer,
in which case the only thing that it transports is the @compressionLevel.
This can be useful in a pipeline featuring ZSTD_compress_usingCDict() exclusively,
expecting a ZSTD_CDict parameter with any data, including those without a known dictionary.
ZSTD_createCDict_byReference() :
Create a digested dictionary for compression
Dictionary content is just referenced, not duplicated.
As a consequence, dictBuffermust outlive CDict,
and its content must remain unmodified throughout the lifetime of CDict.
note: equivalent to ZSTD_createCDict_advanced(), with dictLoadMethod==ZSTD_dlm_byRef
ZSTD_createDDict() :
Create a digested dictionary, ready to start decompression operation without startup delay.
dictBuffer can be released after DDict creation, as its content is copied inside DDict.
ZSTD_createDDict_byReference() :
Create a digested dictionary, ready to start decompression operation without startup delay.
Dictionary content is referenced, and therefore stays in dictBuffer.
It is important that dictBuffer outlives DDict,
it must remain read accessible throughout the lifetime of DDict
ZSTD_dParam_getBounds() :
All parameters must belong to an interval with lower and upper bounds,
otherwise they will either trigger an error or be automatically clamped.
@return : a structure, ZSTD_bounds, which contains
- an error status field, which must be tested using ZSTD_isError()
- both lower and upper bounds, inclusive
ZSTD_decompress() :
compressedSize : must be the exact size of some number of compressed and/or skippable frames.
dstCapacity is an upper bound of originalSize to regenerate.
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()).
ZSTD_decompressBound() :
src should point to the start of a series of ZSTD encoded and/or skippable frames
srcSize must be the exact size of this series
(i.e. there should be a frame boundary at src + srcSize)
@return : - upper-bound for the decompressed size of all data in all successive frames
- if an error occurred: ZSTD_CONTENTSIZE_ERROR
ZSTD_decompressContinue() :
srcSize : must be the exact nb of bytes expected (see ZSTD_nextSrcSizeToDecompress())
@return : nb of bytes generated into dst (necessarily <= `dstCapacity)
or an error code, which can be tested using ZSTD_isError()
ZSTD_decompressStream() :
Streaming decompression function.
Call repetitively to consume full input updating it as necessary.
Function will update both input and output pos fields exposing current state via these fields:
ZSTD_decompressStream_simpleArgs() :
Same as ZSTD_decompressStream(),
but using only integral types as arguments.
This can be helpful for binders from dynamic languages
which have troubles handling structures containing memory pointers.
ZSTD_decompress_usingDict() :
Decompression using a known Dictionary.
Dictionary must be identical to the one used during compression.
Note : This function loads the dictionary, resulting in significant startup delay.
It’s intended for a dictionary used only once.
Note : When dict == NULL || dictSize < 8 no dictionary is used.
ZSTD_decompressionMargin() :
Zstd supports in-place decompression, where the input and output buffers overlap.
In this case, the output buffer must be at least (Margin + Output_Size) bytes large,
and the input buffer must be at the end of the output buffer.
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.
ZSTD_estimateCStreamSize() :
ZSTD_estimateCStreamSize() will provide a budget large enough for any compression level up to selected one.
It will also consider src size to be arbitrarily “large”, which is worst case.
If srcSize is known to always be small, ZSTD_estimateCStreamSize_usingCParams() can provide a tighter estimation.
ZSTD_estimateCStreamSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
ZSTD_estimateCStreamSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParams_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1.
Note : CStream size estimation is only correct for single-threaded compression.
ZSTD_DStream memory budget depends on window Size.
This information can be passed manually, using ZSTD_estimateDStreamSize,
or deducted from a valid frame Header, using ZSTD_estimateDStreamSize_fromFrame();
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
Note 2 : only single-threaded compression is supported.
ZSTD_estimateCStreamSize_usingCCtxParams() will return an error code if ZSTD_c_nbWorkers is >= 1.
Note 3 : ZSTD_estimateCStreamSize* functions are not compatible with the Block-Level Sequence Producer API at this time.
Size estimates assume that no external sequence producer is registered.
ZSTD_estimateDDictSize() :
Estimate amount of memory that will be needed to create a dictionary for decompression.
Note : dictionary created by reference using ZSTD_dlm_byRef are smaller
ZSTD_findDecompressedSize() :
src should point to the start of a series of ZSTD encoded and/or skippable frames
srcSize must be the exact size of this series
(i.e. there should be a frame boundary at src + srcSize)
@return : - decompressed size of all data in all successive frames
- if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN
- if an error occurred: ZSTD_CONTENTSIZE_ERROR
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,
suitable to pass as srcSize to ZSTD_decompress or similar,
or an error code if input is invalid
ZSTD_frameHeaderSize() :
srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX.
@return : size of the Frame Header,
or an error code (if srcSize is too small)
ZSTD_getCParams() :
@return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
estimatedSrcSize value is optional, select 0 if not known
ZSTD_getDecompressedSize() :
NOTE: This function is now obsolete, in favor of ZSTD_getFrameContentSize().
Both functions work the same way, but ZSTD_getDecompressedSize() blends
“empty”, “unknown” and “error” results to the same return value (0),
while ZSTD_getFrameContentSize() gives them separate return values.
@return : decompressed size of src frame content if known and not empty, 0 otherwise.
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.
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.
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.
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 :
ZSTD_getFrameContentSize() :
compatible with legacy mode
@return : decompressed size of the single frame pointed to be src if known, otherwise
- ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined
- ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small)
ZSTD_getFrameHeader() :
decode Frame Header, or requires larger srcSize.
@return : 0, zfhPtr is correctly filled,
>0, srcSize is too small, value is wanted srcSize amount,
or an error code, which can be tested using ZSTD_isError()
ZSTD_getParams() :
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 : contentSize=1, checksum=0, noDictID=0
ZSTD_initCStream_advanced() :
This function is DEPRECATED, and is equivalent to:
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
ZSTD_CCtx_setParams(zcs, params);
ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
ZSTD_CCtx_loadDictionary(zcs, dict, dictSize);
ZSTD_initCStream_srcSize() :
This function is DEPRECATED, and equivalent to:
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any)
ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
ZSTD_initCStream_usingCDict() :
This function is DEPRECATED, and equivalent to:
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
ZSTD_CCtx_refCDict(zcs, cdict);
ZSTD_initCStream_usingCDict_advanced() :
This function is DEPRECATED, and is equivalent to:
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
ZSTD_CCtx_setFParams(zcs, fParams);
ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
ZSTD_CCtx_refCDict(zcs, cdict);
ZSTD_initCStream_usingDict() :
This function is DEPRECATED, and is equivalent to:
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
ZSTD_CCtx_loadDictionary(zcs, dict, dictSize);
ZSTD_initStatic*() :
Initialize an object using a pre-allocated fixed-size buffer.
workspace: The memory area to emplace the object into.
Provided pointer must be 8-bytes aligned.
Buffer must outlive object.
workspaceSize: Use ZSTD_estimate*Size() to determine
how large workspace must be to support target scenario.
@return : pointer to object (same address as workspace, just different type),
or NULL if error (size too small, incorrect alignment, etc.)
Note : zstd will never resize nor malloc() when using a static buffer.
If the object requires more memory than available,
zstd will just error out (typically ZSTD_error_memory_allocation).
Note 2 : there is no corresponding “free” function.
Since workspace is allocated externally, it must be freed externally too.
Note 3 : cParams : use ZSTD_getCParams() to convert a compression level
into its associated cParams.
Limitation 1 : currently not compatible with internal dictionary creation, triggered by
ZSTD_CCtx_loadDictionary(), ZSTD_initCStream_usingDict() or ZSTD_initDStream_usingDict().
Limitation 2 : static cctx currently not compatible with multi-threading.
Limitation 3 : static dctx is incompatible with legacy support.
ZSTD_isFrame() :
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.
ZSTD_loadDEntropy() :
dict : must point at beginning of a valid zstd dictionary.
@return : size of dictionary header (size of magic number + dict ID + entropy tables)
ZSTD_mergeBlockDelimiters() :
Given an array of ZSTD_Sequence, remove all sequences that represent block delimiters/last literals
by merging them into the literals of the next sequence.
ZSTD_resetCStream() :
This function is DEPRECATED, and is equivalent to:
ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
Note: ZSTD_resetCStream() interprets pledgedSrcSize == 0 as ZSTD_CONTENTSIZE_UNKNOWN, but
ZSTD_CCtx_setPledgedSrcSize() does not do the same, so ZSTD_CONTENTSIZE_UNKNOWN must be
explicitly specified.
ZSTD_sequenceBound() :
srcSize : size of the input buffer
@return : upper-bound for the number of sequences that can be generated
from a buffer of srcSize bytes
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.
ZSTD_toFlushNow() :
Tell how many bytes are ready to be flushed immediately.
Useful for multithreading scenarios (nbWorkers >= 1).
Probe the oldest active job, defined as oldest job not yet entirely flushed,
and check its output buffer.
@return : amount of data stored in oldest job and ready to be flushed immediately.
if @return == 0, it means either :
Custom memory allocation :
These prototypes make it possible to pass your own allocation/free functions.
ZSTD_customMem is provided at creation time, using ZSTD_create*_advanced() variants listed below.
All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones.
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.