879 lines
55 KiB
HTML
879 lines
55 KiB
HTML
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
|
|
<title>zstd 1.3.0 Manual</title>
|
|
</head>
|
|
<body>
|
|
<h1>zstd 1.3.0 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">Frame size functions</a></li>
|
|
<li><a href="#Chapter13">Context memory usage</a></li>
|
|
<li><a href="#Chapter14">Advanced compression functions</a></li>
|
|
<li><a href="#Chapter15">Advanced decompression functions</a></li>
|
|
<li><a href="#Chapter16">Advanced streaming functions</a></li>
|
|
<li><a href="#Chapter17">Buffer-less and synchronous inner streaming functions</a></li>
|
|
<li><a href="#Chapter18">Buffer-less streaming compression (synchronous mode)</a></li>
|
|
<li><a href="#Chapter19">Buffer-less streaming decompression (synchronous mode)</a></li>
|
|
<li><a href="#Chapter20">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 currently 22.
|
|
Levels >= 20, labeled `--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>/**< 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 some number of compressed and/or skippable frames.
|
|
`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> NOTE: This function is planned to be obsolete, in favor of ZSTD_getFrameContentSize().
|
|
ZSTD_getFrameContentSize() works the same way,
|
|
returning the decompressed size of a single frame,
|
|
but distinguishes empty frames from frames with an unknown size, or errors.
|
|
|
|
'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, it may not be present, typically 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 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></pre><b><pre>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>
|
|
</pre></b><BR>
|
|
<a name="Chapter4"></a><h2>Explicit memory management</h2><pre></pre>
|
|
|
|
<h3>Compression context</h3><pre> When compressing many times,
|
|
it is recommended to allocate a context just once, and re-use it for each successive compression operation.
|
|
This will make workload friendlier for system's memory.
|
|
Use one context per thread for parallel execution in multi-threaded environments.
|
|
</pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx;
|
|
ZSTD_CCtx* ZSTD_createCCtx(void);
|
|
size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx);
|
|
</pre></b><BR>
|
|
<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> When decompressing many times,
|
|
it is recommended to allocate a context only once,
|
|
and re-use it for each successive compression operation.
|
|
This will make workload friendlier for system's memory.
|
|
Use one context per thread for parallel execution.
|
|
</pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx;
|
|
ZSTD_DCtx* ZSTD_createDCtx(void);
|
|
size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
|
|
</pre></b><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* dictBuffer, 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.
|
|
`dictBuffer` can be released after ZSTD_CDict creation, as its content is copied within CDict
|
|
</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.
|
|
Frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize);
|
|
</b><p> 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
|
|
</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>typedef ZSTD_CCtx ZSTD_CStream; </b>/**< CCtx and CStream are effectively same object */<b>
|
|
</b></pre><BR>
|
|
<h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void);
|
|
size_t ZSTD_freeCStream(ZSTD_CStream* zcs);
|
|
</pre></b><BR>
|
|
<h3>Streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel);
|
|
size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
|
|
size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
|
|
size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
|
|
</pre></b><BR>
|
|
<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>
|
|
|
|
<h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void);
|
|
size_t ZSTD_freeDStream(ZSTD_DStream* zds);
|
|
</pre></b><BR>
|
|
<h3>Streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_initDStream(ZSTD_DStream* zds);
|
|
size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
|
|
</pre></b><BR>
|
|
<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=1, ZSTD_dfast, ZSTD_greedy, ZSTD_lazy, ZSTD_lazy2,
|
|
ZSTD_btlazy2, ZSTD_btopt, ZSTD_btultra } 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 (when known) */<b>
|
|
unsigned checksumFlag; </b>/**< 1: generate a 32-bits checksum at end of frame, for error detection */<b>
|
|
unsigned noDictIDFlag; </b>/**< 1: no dictID 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>
|
|
<pre><b>typedef struct {
|
|
unsigned long long frameContentSize;
|
|
unsigned windowSize;
|
|
unsigned dictID;
|
|
unsigned checksumFlag;
|
|
} ZSTD_frameHeader;
|
|
</b></pre><BR>
|
|
<h3>Custom memory allocation functions</h3><pre></pre><b><pre>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;
|
|
</pre></b><BR>
|
|
<a name="Chapter12"></a><h2>Frame size functions</h2><pre></pre>
|
|
|
|
<pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize);
|
|
</b><p> `src` should point to the start of a ZSTD encoded frame or skippable frame
|
|
`srcSize` must be at least as large as the frame
|
|
@return : the compressed size of the frame pointed to by `src`,
|
|
suitable to pass to `ZSTD_decompress` or similar,
|
|
or an error code if given invalid input.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>#define ZSTD_CONTENTSIZE_UNKNOWN (0ULL - 1)
|
|
#define ZSTD_CONTENTSIZE_ERROR (0ULL - 2)
|
|
unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize);
|
|
</b><p> `src` should point to the start of a ZSTD encoded frame.
|
|
`srcSize` must be at least as large as the frame header.
|
|
A value >= `ZSTD_frameHeaderSize_max` is guaranteed to be large enough.
|
|
@return : - decompressed size of the frame pointed to be `src` if known
|
|
- ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined
|
|
- ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small)
|
|
</p></pre><BR>
|
|
|
|
<pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
|
|
</b><p> `src` should point 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 exactly `srcSize` bytes after `src`)
|
|
@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
|
|
|
|
note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
|
|
When `return==ZSTD_CONTENTSIZE_UNKNOWN`, 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 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to
|
|
read each contained frame header. This is efficient as most of the data is skipped,
|
|
however it does mean that all frame data must be present and valid.
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter13"></a><h2>Context memory usage</h2><pre></pre>
|
|
|
|
<pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
|
|
size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
|
|
size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
|
|
size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
|
|
size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
|
|
size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
|
|
</b><p> These functions give the current memory usage of selected object.
|
|
Object memory usage can evolve if it's re-used multiple times.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
|
|
size_t ZSTD_estimateDCtxSize(void);
|
|
</b><p> These functions make it possible to estimate memory usage
|
|
of a future target object, before its allocation,
|
|
given a set of parameters, which vary depending on target object.
|
|
The objective is to guide decision before allocation.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_estimateCStreamSize(ZSTD_compressionParameters cParams);
|
|
size_t ZSTD_estimateDStreamSize(ZSTD_frameHeader fHeader);
|
|
</b><p> Note : if streaming is init with function ZSTD_init?Stream_usingDict(),
|
|
an internal ?Dict will be created, which size is not estimated.
|
|
In this case, get additional size by using ZSTD_estimate?DictSize
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_estimateCDictSize(ZSTD_compressionParameters cParams, size_t dictSize);
|
|
size_t ZSTD_estimateDDictSize(size_t dictSize);
|
|
</b><p> Note : if dictionary is created "byReference", reduce estimation by dictSize
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter14"></a><h2>Advanced compression functions</h2><pre></pre>
|
|
|
|
<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>typedef enum {
|
|
ZSTD_p_forceWindow, </b>/* Force back-references to remain < windowSize, even when referencing Dictionary content (default:0) */<b>
|
|
ZSTD_p_forceRawDict </b>/* Force loading dictionary in "content-only" mode (no header analysis) */<b>
|
|
} ZSTD_CCtxParameter;
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_setCCtxParameter(ZSTD_CCtx* cctx, ZSTD_CCtxParameter param, unsigned value);
|
|
</b><p> Set advanced parameters, selected through enum ZSTD_CCtxParameter
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError())
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel);
|
|
</b><p> Create a digested dictionary for compression
|
|
Dictionary content is simply referenced, and therefore stays in dictBuffer.
|
|
It is important that dictBuffer outlives CDict, it must remain read accessible throughout the lifetime of CDict
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize, unsigned byReference,
|
|
ZSTD_compressionParameters cParams, ZSTD_customMem customMem);
|
|
</b><p> Create a ZSTD_CDict using external alloc and free, and customized compression parameters
|
|
</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* cctx,
|
|
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 over each compression parameter
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx,
|
|
void* dst, size_t dstCapacity,
|
|
const void* src, size_t srcSize,
|
|
const ZSTD_CDict* cdict, ZSTD_frameParameters fParams);
|
|
</b><p> Same as ZSTD_compress_usingCDict(), with fine-tune control over frame parameters
|
|
</p></pre><BR>
|
|
|
|
<h3>New experimental advanced parameters API</h3><pre></pre><b><pre></pre></b><BR>
|
|
<pre><b>typedef enum {
|
|
</b>/* compression parameters */<b>
|
|
ZSTD_p_compressionLevel=100, </b>/* Update all compression parameters according to pre-defined cLevel table<b>
|
|
* Default level is 3.
|
|
* Special: value 0 means "do not change cLevel". */
|
|
ZSTD_p_windowLog, </b>/* Maximum allowed back-reference distance, expressed as power of 2.<b>
|
|
* Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX.
|
|
* default value : set through compressionLevel.
|
|
* Special: value 0 means "do not change windowLog". */
|
|
ZSTD_p_hashLog, </b>/* Size of the probe table, as a power of 2.<b>
|
|
* Resulting table size is (1 << (hashLog+2)).
|
|
* Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX.
|
|
* Larger tables improve compression ratio of strategies <= dFast,
|
|
* and improve speed of strategies > dFast.
|
|
* Special: value 0 means "do not change hashLog". */
|
|
ZSTD_p_chainLog, </b>/* Size of the full-search table, as a power of 2.<b>
|
|
* Resulting table size is (1 << (chainLog+2)).
|
|
* Larger tables result in better and slower compression.
|
|
* This parameter is useless when using "fast" strategy.
|
|
* Special: value 0 means "do not change chainLog". */
|
|
ZSTD_p_searchLog, </b>/* Number of search attempts, as a power of 2.<b>
|
|
* More attempts result in better and slower compression.
|
|
* This parameter is useless when using "fast" and "dFast" strategies.
|
|
* Special: value 0 means "do not change searchLog". */
|
|
ZSTD_p_minMatch, </b>/* Minimum size of searched matches (note : repCode matches can be smaller).<b>
|
|
* Larger values make faster compression and decompression, but decrease ratio.
|
|
* Must be clamped between ZSTD_SEARCHLENGTH_MIN and ZSTD_SEARCHLENGTH_MAX.
|
|
* Note that currently, for all strategies < btopt, effective minimum is 4.
|
|
* Note that currently, for all strategies > fast, effective maximum is 6.
|
|
* Special: value 0 means "do not change minMatchLength". */
|
|
ZSTD_p_targetLength, </b>/* Only useful for strategies >= btopt.<b>
|
|
* Length of Match considered "good enough" to stop search.
|
|
* Larger values make compression stronger and slower.
|
|
* Special: value 0 means "do not change targetLength". */
|
|
ZSTD_p_compressionStrategy, </b>/* See ZSTD_strategy enum definition.<b>
|
|
* Cast selected strategy as unsigned for ZSTD_CCtx_setParameter() compatibility.
|
|
* The higher the value of selected strategy, the more complex it is,
|
|
* resulting in stronger and slower compression.
|
|
* Special: value 0 means "do not change strategy". */
|
|
#if 0
|
|
ZSTD_p_windowSize, </b>/* Maximum allowed back-reference distance.<b>
|
|
* Can be set to a more precise value than windowLog.
|
|
* Will be transparently reduced to closest possible inferior value
|
|
* (see Zstandard compression format) */
|
|
</b>/* Not ready yet ! */<b>
|
|
#endif
|
|
|
|
</b>/* frame parameters */<b>
|
|
ZSTD_p_contentSizeFlag=200, </b>/* Content size is written into frame header _whenever known_ (default:1) */<b>
|
|
ZSTD_p_checksumFlag, </b>/* A 32-bits checksum of content is written at end of frame (default:0) */<b>
|
|
ZSTD_p_dictIDFlag, </b>/* When applicable, dictID of dictionary is provided in frame header (default:1) */<b>
|
|
|
|
</b>/* dictionary parameters */<b>
|
|
ZSTD_p_refDictContent=300, </b>/* Content of dictionary content will be referenced, instead of copied (default:0).<b>
|
|
* This avoids duplicating dictionary content.
|
|
* But it also requires that dictionary buffer outlives its user (CDict) */
|
|
</b>/* Not ready yet ! */<b>
|
|
ZSTD_p_rawContentDict, </b>/* load dictionary in "content-only" mode (no header analysis) (default:0) */<b>
|
|
</b>/* question : should there be an option to load dictionary only in zstd format, rejecting others with an error code ? */<b>
|
|
|
|
#if 0
|
|
</b>/* multi-threading parameters (not ready yet !) */<b>
|
|
ZSTD_p_nbThreads=400, </b>/* Select how many threads a compression job can spawn (default:1)<b>
|
|
* More threads improve speed, but increases also memory usage */
|
|
ZSTDMT_p_jobSize, </b>/* Size of a compression job. Each job is compressed in parallel.<b>
|
|
* 0 means default, which is dynamically determined based on compression parameters.
|
|
* Job size must be a minimum of overlapSize, or 1 KB, whichever is largest
|
|
* The minimum size is automatically and transparently enforced */
|
|
ZSTDMT_p_overlapSizeLog, </b>/* Size of previous input reloaded at the beginning of each job.<b>
|
|
* 0 => no overlap, 6(default) => use 1/8th of windowSize, >=9 => use full windowSize */
|
|
#endif
|
|
|
|
</b>/* advanced parameters - may not remain available after API update */<b>
|
|
ZSTD_p_forceMaxWindow=1100, </b>/* Force back-references to remain < windowSize,<b>
|
|
* even when referencing into Dictionary content
|
|
* default : 0 when using a CDict, 1 when using a Prefix */
|
|
} ZSTD_cParameter;
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, unsigned value);
|
|
</b><p> Set one compression parameter, selected by enum ZSTD_cParameter.
|
|
Note : when `value` is an enum, cast it to unsigned for proper type checking.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize);
|
|
</b><p> Total input data size to be compressed into a single frame.
|
|
This value will be controlled at the end, and result in error if not respected.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Note 1 : 0 means zero, empty.
|
|
In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN.
|
|
Note that ZSTD_CONTENTSIZE_UNKNOWN is default value for all new compression jobs.
|
|
Note 2 : If all data is provided and consumed in a single round,
|
|
this value is overriden by srcSize instead.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize); </b>/* Not ready yet ! */<b>
|
|
</b><p> Create an internal CDict from dict buffer.
|
|
Decompression will have to use same buffer.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Special : Adding a NULL (or 0-size) dictionary invalidates any previous prefix,
|
|
meaning "return to no-dictionary mode".
|
|
Note 1 : Dictionary content will be copied internally,
|
|
except if ZSTD_p_refDictContent is set.
|
|
Note 2 : Loading a dictionary involves building tables, which are dependent on compression parameters.
|
|
For this reason, compression parameters cannot be changed anymore after loading a prefix.
|
|
It's also a CPU-heavy operation, with non-negligible impact on latency.
|
|
Note 3 : Dictionary will be used for all future compression jobs.
|
|
To return to "no-dictionary" situation, load a NULL dictionary
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx, const void* prefix, size_t prefixSize); </b>/* Not ready yet ! */<b>
|
|
</b><p> Reference a prefix (content-only dictionary) to bootstrap next compression job.
|
|
Decompression will have to use same prefix.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Special : Adding a NULL (or 0-size) dictionary invalidates any previous prefix, meaning "return to no-dictionary mode".
|
|
Note 1 : Prefix buffer is referenced. It must outlive compression job.
|
|
Note 3 : Prefix is only used once. Tables are discarded at end of compression job.
|
|
If there is a need to use same prefix multiple times, consider embedding it into a ZSTD_CDict.
|
|
Note 2 : Referencing a prefix involves building tables, which are dependent on compression parameters.
|
|
For this reason, compression parameters cannot be changed anymore after loading a prefix.
|
|
It's also a CPU-heavy operation, with non-negligible impact on latency.
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_CDict* ZSTD_CDict_createEmpty(void); </b>/* Not ready yet ! */<b>
|
|
size_t ZSTD_CDict_setParameter(ZSTD_CDict* cdict, ZSTD_cParameter param, unsigned value); </b>/* Not ready yet ! */<b>
|
|
size_t ZSTD_CDict_loadDictionary(ZSTD_CDict* cdict, const void* dict, size_t dictSize); </b>/* Not ready yet ! */<b>
|
|
</b><p> Create a CDict object which is still mutable after creation.
|
|
It's the only one case allowing usage of ZSTD_CDict_setParameter().
|
|
Once all compression parameters are selected,
|
|
it's possible to load the target dictionary, using ZSTD_CDict_loadDictionary().
|
|
Dictionary content will be copied internally (except if ZSTD_p_refDictContent is set).
|
|
After loading the dictionary, no more change is possible.
|
|
The only remaining operation is to free CDict object.
|
|
Note : An unfinished CDict behaves the same as a NULL CDict if referenced into a CCtx.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/* Not ready yet ! */<b>
|
|
</b><p> Add a prepared dictionary to cctx, to be used for next compression jobs.
|
|
Note that compression parameters will be enforced from within CDict.
|
|
Currently, they supercede any compression parameter previously set within CCtx.
|
|
The dictionary will remain valid for future compression jobs using same cctx.
|
|
@result : 0, or an error code (which can be tested with ZSTD_isError()).
|
|
Special : adding a NULL CDict means "return to no-dictionary mode".
|
|
Note 1 : Currently, only one dictionary can be managed.
|
|
Adding a new dictionary effectively "discards" any previous one.
|
|
Note 2 : CDict is just referenced, its lifetime must outlive CCtx.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>typedef enum {
|
|
ZSTD_e_continue=0, </b>/* collect more data, encoder transparently decides when to output result, for optimal conditions */<b>
|
|
ZSTD_e_flush, </b>/* flush any data provided so far - frame will continue, future data can still reference previous data for better compression */<b>
|
|
ZSTD_e_end </b>/* flush any remaining data and ends current frame. Any future compression starts a new frame. */<b>
|
|
} ZSTD_EndDirective;
|
|
</b></pre><BR>
|
|
<pre><b>size_t ZSTD_compress_generic (ZSTD_CCtx* cctx,
|
|
ZSTD_outBuffer* output,
|
|
ZSTD_inBuffer* input,
|
|
ZSTD_EndDirective endOp);
|
|
</b><p> Behave about the same as ZSTD_compressStream. To note :
|
|
- Compression parameters are pushed into CCtx before starting compression, using ZSTD_setCCtxParameter()
|
|
- Compression parameters cannot be changed once compression is started.
|
|
- *dstPos must be <= dstCapacity, *srcPos must be <= srcSize
|
|
- *dspPos and *srcPos will be updated. They are guaranteed to remain below their respective limit.
|
|
- @return provides the amount of data ready to flush within internal buffers
|
|
or an error code, which can be tested using ZSTD_isError().
|
|
if @return != 0, flush is not fully completed, and must be called again to empty internal buffers.
|
|
- after a ZSTD_e_end directive, if internal buffer is not fully flushed,
|
|
only ZSTD_e_end and ZSTD_e_flush operations are allowed.
|
|
It is necessary to fully flush internal buffers
|
|
before changing compression parameters or start a new compression job.
|
|
|
|
</p></pre><BR>
|
|
|
|
<pre><b>size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx); </b>/* Not ready yet ! */<b>
|
|
</b><p> Return a CCtx to clean state.
|
|
Useful after an error, or to interrupt an ongoing compression job and start a new one.
|
|
It's possible to modify compression parameters after a reset.
|
|
Any internal data not yet flushed is cancelled.
|
|
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter15"></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>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>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize);
|
|
</b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
|
|
Dictionary content is simply referenced, and therefore stays in dictBuffer.
|
|
It is important that dictBuffer outlives DDict, it must remain read accessible throughout the lifetime of DDict
|
|
</p></pre><BR>
|
|
|
|
<pre><b>ZSTD_DDict* ZSTD_createDDict_advanced(const void* dict, size_t dictSize,
|
|
unsigned byReference, ZSTD_customMem customMem);
|
|
</b><p> Create a ZSTD_DDict using external alloc and free, optionally by reference
|
|
</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 use ZSTD_getFrameParams(), which will provide a more precise error code.
|
|
</p></pre><BR>
|
|
|
|
<a name="Chapter16"></a><h2>Advanced streaming functions</h2><pre></pre>
|
|
|
|
<h3>Advanced Streaming compression functions</h3><pre></pre><b><pre>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, a size of 0 means unknown. for a frame size of 0 use initCStream_advanced */<b>
|
|
size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); </b>/**< note: a dict will not be used if dict == NULL or dictSize < 8. This result in the creation of an internal CDict */<b>
|
|
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 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */<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_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, unsigned long long pledgedSrcSize, ZSTD_frameParameters fParams); </b>/**< same as ZSTD_initCStream_usingCDict(), with control over frame parameters */<b>
|
|
</pre></b><BR>
|
|
<pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize);
|
|
</b><p> start a new compression job, using same parameters from previous job.
|
|
This is typically useful to skip dictionary loading stage, since it will re-use it in-place..
|
|
Note that zcs must be init at least once before using ZSTD_resetCStream().
|
|
pledgedSrcSize==0 means "srcSize unknown".
|
|
If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end.
|
|
@return : 0, or an error code (which can be tested using ZSTD_isError())
|
|
</p></pre><BR>
|
|
|
|
<h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre>typedef enum { DStream_p_maxWindowSize } ZSTD_DStreamParameter_e;
|
|
ZSTD_DStream* ZSTD_createDStream_advanced(ZSTD_customMem customMem);
|
|
size_t ZSTD_setDStreamParameter(ZSTD_DStream* zds, ZSTD_DStreamParameter_e paramType, unsigned paramValue);
|
|
size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize); </b>/**< note: a dict will not be used if dict == NULL or dictSize < 8 */<b>
|
|
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>
|
|
</pre></b><BR>
|
|
<a name="Chapter17"></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="Chapter18"></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 srcSize==0, in which case, it will write a final empty block to end the frame.
|
|
Without last block mark, frames will be considered unfinished (corrupted) by decoders.
|
|
|
|
`ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress some new frame.
|
|
<BR></pre>
|
|
|
|
<h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>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); </b>/**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */<b>
|
|
size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b>
|
|
size_t ZSTD_compressBegin_usingCDict_advanced(ZSTD_CCtx* const cctx, const ZSTD_CDict* const cdict, ZSTD_frameParameters const fParams, unsigned long long const pledgedSrcSize); </b>/* compression parameters are already set within cdict. pledgedSrcSize=0 means null-size */<b>
|
|
size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize); </b>/**< note: if pledgedSrcSize can be 0, indicating unknown size. if it is non-zero, it must be accurate. for 0 size frames, use compressBegin_advanced */<b>
|
|
</pre></b><BR>
|
|
<a name="Chapter19"></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().
|
|
If decompression requires a dictionary, use ZSTD_decompressBegin_usingDict() or ZSTD_decompressBegin_usingDDict().
|
|
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.
|
|
Note : If fparamsPtr->frameContentSize==0, it is ambiguous: the frame might actually be a Zstd encoded frame with no content.
|
|
For purposes of decompression, it is valid in both cases to skip the frame using
|
|
ZSTD_findFrameCompressedSize to find its size in bytes.
|
|
It also returns Frame Size as fparamsPtr->frameContentSize.
|
|
<BR></pre>
|
|
|
|
<h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_getFrameHeader(ZSTD_frameHeader* zfhPtr, 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);
|
|
size_t ZSTD_decompressBegin_usingDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict);
|
|
void ZSTD_copyDCtx(ZSTD_DCtx* dctx, const ZSTD_DCtx* preparedDCtx);
|
|
</pre></b><BR>
|
|
<pre><b>typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
|
|
</b></pre><BR>
|
|
<a name="Chapter20"></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 : any ZSTD_compressBegin*() variant, including with dictionary
|
|
+ decompression : any ZSTD_decompressBegin*() variant, including with dictionary
|
|
+ copyCCtx() and copyDCtx() can be used too
|
|
- Block size is limited, it must be <= ZSTD_getBlockSizeMax() <= ZSTD_BLOCKSIZE_ABSOLUTEMAX
|
|
+ If input is larger than a block size, it's necessary to split input data into multiple blocks
|
|
+ For inputs larger than a single block size, consider using the regular ZSTD_compress() instead.
|
|
Frame metadata is not that costly, and quickly becomes negligible as source size grows larger.
|
|
- 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, should some of them be uncompressed,
|
|
decoder must be informed of their existence in order to follow proper history.
|
|
Use ZSTD_insertBlock() for such a case.
|
|
<BR></pre>
|
|
|
|
<h3>Raw zstd block functions</h3><pre></pre><b><pre>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>
|
|
</pre></b><BR>
|
|
</html>
|
|
</body>
|