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LZ4 Block Format Description
============================
Last revised: 2022-07-31 .
Author : Yann Collet
This specification is intended for developers willing to
produce or read LZ4 compressed data blocks
using any programming language of their choice.
LZ4 is an LZ77-type compressor with a fixed byte-oriented encoding format.
There is no entropy encoder back-end nor framing layer.
The latter is assumed to be handled by other parts of the system
(see [LZ4 Frame format]).
This design is assumed to favor simplicity and speed.
This document describes only the Block Format,
not how the compressor nor decompressor actually work.
For more details on such topics, see later section "Implementation Notes".
[LZ4 Frame format]: lz4_Frame_format.md
Compressed block format
-----------------------
An LZ4 compressed block is composed of sequences.
A sequence is a suite of literals (not-compressed bytes),
followed by a match copy operation.
Each sequence starts with a `token`.
The `token` is a one byte value, separated into two 4-bits fields.
Therefore each field ranges from 0 to 15.
The first field uses the 4 high-bits of the token.
It provides the length of literals to follow.
If the field value is smaller than 15,
then it represents the total nb of literals present in the sequence,
including 0, in which case there is no literal.
The value 15 is a special case: more bytes are required to indicate the full length.
Each additional byte then represents a value from 0 to 255,
which is added to the previous value to produce a total length.
When the byte value is 255, another byte must be read and added, and so on.
There can be any number of bytes of value `255` following `token`.
The Block Format does not define any "size limit",
though real implementations may feature some practical limits
(see more details in later chapter "Implementation Notes").
Note : this format explains why a non-compressible input block is expanded by 0.4%.
Example 1 : A literal length of 48 will be represented as :
- 15 : value for the 4-bits High field
- 33 : (=48-15) remaining length to reach 48
Example 2 : A literal length of 280 will be represented as :
- 15 : value for the 4-bits High field
- 255 : following byte is maxed, since 280-15 >= 255
- 10 : (=280 - 15 - 255) remaining length to reach 280
Example 3 : A literal length of 15 will be represented as :
- 15 : value for the 4-bits High field
- 0 : (=15-15) yes, the zero must be output
Following `token` and optional length bytes, are the literals themselves.
They are exactly as numerous as just decoded (length of literals).
Reminder: it's possible that there are zero literals.
Following the literals is the match copy operation.
It starts by the `offset` value.
This is a 2 bytes value, in little endian format
(the 1st byte is the "low" byte, the 2nd one is the "high" byte).
The `offset` represents the position of the match to be copied from the past.
For example, 1 means "current position - 1 byte".
The maximum `offset` value is 65535. 65536 and beyond cannot be coded.
Note that 0 is an invalid `offset` value.
The presence of a 0 `offset` value denotes an invalid (corrupted) block.
Then the `matchlength` can be extracted.
For this, we use the second `token` field, the low 4-bits.
Such a value, obviously, ranges from 0 to 15.
However here, 0 means that the copy operation is minimal.
The minimum length of a match, called `minmatch`, is 4.
As a consequence, a 0 value means 4 bytes.
Similarly to literal length, any value smaller than 15 represents a length,
to which 4 (`minmatch`) must be added, thus ranging from 4 to 18.
A value of 15 is special, meaning 19+ bytes,
to which one must read additional bytes, one at a time,
with each byte value ranging from 0 to 255.
They are added to total to provide the final match length.
A 255 value means there is another byte to read and add.
There is no limit to the number of optional `255` bytes that can be present,
and therefore no limit to representable match length,
though real-life implementations are likely going to enforce limits for practical reasons (see more details in "Implementation Notes" section below).
Note: this format has a maximum achievable compression ratio of about ~250.
Decoding the `matchlength` reaches the end of current sequence.
Next byte will be the start of another sequence, and therefore a new `token`.
End of block conditions
-------------------------
There are specific restrictions required to terminate an LZ4 block.
1. The last sequence contains only literals.
The block ends right after the literals (no `offset` field).
2. The last 5 bytes of input are always literals.
Therefore, the last sequence contains at least 5 bytes.
- Special : if input is smaller than 5 bytes,
there is only one sequence, it contains the whole input as literals.
Even empty input can be represented, using a zero byte,
interpreted as a final token without literal and without a match.
3. The last match must start at least 12 bytes before the end of block.
The last match is part of the _penultimate_ sequence.
It is followed by the last sequence, which contains _only_ literals.
- Note that, as a consequence,
blocks < 12 bytes cannot be compressed.
And as an extension, _independent_ blocks < 13 bytes cannot be compressed,
because they must start by at least one literal,
that the match can then copy afterwards.
When a block does not respect these end conditions,
a conformant decoder is allowed to reject the block as incorrect.
These rules are in place to ensure compatibility with
a wide range of historical decoders
which rely on these conditions for their speed-oriented design.
Implementation notes
-----------------------
The LZ4 Block Format only defines the compressed format,
it does not tell how to create a decoder or an encoder,
which design is left free to the imagination of the implementer.
However, thanks to experience, there are a number of typical topics that
most implementations will have to consider.
This section tries to provide a few guidelines.
#### Metadata
An LZ4-compressed Block requires additional metadata for proper decoding.
Typically, a decoder will require the compressed block's size,
and an upper bound of decompressed size.
Other variants exist, such as knowing the decompressed size,
and having an upper bound of the input size.
The Block Format does not specify how to transmit such information,
which is considered an out-of-band information channel.
That's because in many cases, the information is present in the environment.
For example, databases must store the size of their compressed block for indexing,
and know that their decompressed block can't be larger than a certain threshold.
If you need a format which is "self-contained",
and also transports the necessary metadata for proper decoding on any platform,
consider employing the [LZ4 Frame format] instead.
#### Large lengths
While the Block Format does not define any maximum value for length fields,
in practice, most implementations will feature some form of limit,
since it's expected for such values to be stored into registers of fixed bit width.
If length fields use 64-bit registers,
then it can be assumed that there is no practical limit,
as it would require a single continuous block of multiple petabytes to reach it,
which is unreasonable by today's standard.
If length fields use 32-bit registers, then it can be overflowed,
but requires a compressed block of size > 16 MB.
Therefore, implementations that do not deal with compressed blocks > 16 MB are safe.
However, if such a case is allowed,
then it's recommended to check that no large length overflows the register.
If length fields use 16-bit registers,
then it's definitely possible to overflow such register,
with less than < 300 bytes of compressed data.
A conformant decoder should be able to detect length overflows when it's possible,
and simply error out when that happens.
The input block might not be invalid,
it's just not decodable by the local decoder implementation.
Note that, in order to be compatible with the larger LZ4 ecosystem,
it's recommended to be able to read and represent lengths of up to 4 MB,
and to accept blocks of size up to 4 MB.
Such limits are compatible with 32-bit length registers,
and prevent overflow of 32-bit registers.
#### Safe decoding
If a decoder receives compressed data from any external source,
it is recommended to ensure that the decoder is resilient to corrupted input,
and made safe from buffer overflow manipulations.
Always ensure that read and write operations
remain within the limits of provided buffers.
Of particular importance, ensure that the nb of bytes instructed to copy
does not overflow neither the input nor the output buffers.
Ensure also, when reading an offset value, that the resulting position to copy
does not reach beyond the beginning of the buffer.
Such a situation can happen during the first 64 KB of decoded data.
For more safety, test the decoder with fuzzers
to ensure it's resilient to improbable sequences of conditions.
Combine them with sanitizers, in order to catch overflows (asan)
or initialization issues (msan).
Pay some attention to offset 0 scenario, which is invalid,
and therefore must not be blindly decoded:
a naive implementation could preserve destination buffer content,
which could then result in information disclosure
if such buffer was uninitialized and still containing private data.
For reference, in such a scenario, the reference LZ4 decoder
clears the match segment with `0` bytes,
though other solutions are certainly possible.
Finally, pay attention to the "overlap match" scenario,
when `matchlength` is larger than `offset`.
In which case, since `match_pos + matchlength > current_pos`,
some of the later bytes to copy do not exist yet,
and will be generated during the early stage of match copy operation.
Such scenario must be handled with special care.
A common case is an offset of 1,
meaning the last byte is repeated `matchlength` times.
#### Compression techniques
The core of a LZ4 compressor is to detect duplicated data across past 64 KB.
The format makes no assumption nor limits to the way a compressor
searches and selects matches within the source data block.
For example, an upper compression limit can be reached,
using a technique called "full optimal parsing", at high cpu and memory cost.
But multiple other techniques can be considered,
featuring distinct time / performance trade-offs.
As long as the specified format is respected,
the result will be compatible with and decodable by any compliant decoder.

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LZ4 Frame Format Description
============================
### Notices
Copyright (c) 2013-2020 Yann Collet
Permission is granted to copy and distribute this document
for any purpose and without charge,
including translations into other languages
and incorporation into compilations,
provided that the copyright notice and this notice are preserved,
and that any substantive changes or deletions from the original
are clearly marked.
Distribution of this document is unlimited.
### Version
1.6.4 (28/12/2023)
Introduction
------------
The purpose of this document is to define a lossless compressed data format,
that is independent of CPU type, operating system,
file system and character set, suitable for
File compression, Pipe and streaming compression
using the [LZ4 algorithm](http://www.lz4.org).
The data can be produced or consumed,
even for an arbitrarily long sequentially presented input data stream,
using only an a priori bounded amount of intermediate storage,
and hence can be used in data communications.
The format uses the LZ4 compression method,
and optional [xxHash-32 checksum method](https://github.com/Cyan4973/xxHash),
for detection of data corruption.
The data format defined by this specification
does not attempt to allow random access to compressed data.
This specification is intended for use by implementers of software
to compress data into LZ4 format and/or decompress data from LZ4 format.
The text of the specification assumes a basic background in programming
at the level of bits and other primitive data representations.
Unless otherwise indicated below,
a compliant compressor must produce data sets
that conform to the specifications presented here.
It doesn't need to support all options though.
A compliant decompressor must be able to decompress
at least one working set of parameters
that conforms to the specifications presented here.
It may also ignore checksums.
Whenever it does not support a specific parameter within the compressed stream,
it must produce a non-ambiguous error code
and associated error message explaining which parameter is unsupported.
General Structure of LZ4 Frame format
-------------------------------------
| MagicNb | F. Descriptor | Data Block | (...) | EndMark | C. Checksum |
|:-------:|:-------------:| ---------- | ----- | ------- | ----------- |
| 4 bytes | 3-15 bytes | | | 4 bytes | 0-4 bytes |
__Magic Number__
4 Bytes, Little endian format.
Value : 0x184D2204
__Frame Descriptor__
3 to 15 Bytes, to be detailed in its own paragraph,
as it is the most important part of the spec.
The combined _Magic_Number_ and _Frame_Descriptor_ fields are sometimes
called ___LZ4 Frame Header___. Its size varies between 7 and 19 bytes.
__Data Blocks__
To be detailed in its own paragraph.
That’s where compressed data is stored.
__EndMark__
The flow of blocks ends when the last data block is followed by
the 32-bit value `0x00000000`.
__Content Checksum__
_Content_Checksum_ verify that the full content has been decoded correctly.
The content checksum is the result of [xxHash-32 algorithm]
digesting the original (decoded) data as input, and a seed of zero.
Content checksum is only present when its associated flag
is set in the frame descriptor.
Content Checksum validates the result,
that all blocks were fully transmitted in the correct order and without error,
and also that the encoding/decoding process itself generated no distortion.
Its usage is recommended.
The combined _EndMark_ and _Content_Checksum_ fields might sometimes be
referred to as ___LZ4 Frame Footer___. Its size varies between 4 and 8 bytes.
__Frame Concatenation__
In some circumstances, it may be preferable to append multiple frames,
for example in order to add new data to an existing compressed file
without re-framing it.
In such case, each frame has its own set of descriptor flags.
Each frame is considered independent.
The only relation between frames is their sequential order.
The ability to decode multiple concatenated frames
within a single stream or file
is left outside of this specification.
As an example, the reference lz4 command line utility behavior is
to decode all concatenated frames in their sequential order.
Frame Descriptor
----------------
| FLG | BD | (Content Size) | (Dictionary ID) | HC |
| ------- | ------- |:--------------:|:---------------:| ------- |
| 1 byte | 1 byte | 0 - 8 bytes | 0 - 4 bytes | 1 byte |
The descriptor uses a minimum of 3 bytes,
and up to 15 bytes depending on optional parameters.
__FLG byte__
| BitNb | 7-6 | 5 | 4 | 3 | 2 | 1 | 0 |
| ------- |-------|-------|----------|------|----------|----------|------|
|FieldName|Version|B.Indep|B.Checksum|C.Size|C.Checksum|*Reserved*|DictID|
__BD byte__
| BitNb | 7 | 6-5-4 | 3-2-1-0 |
| ------- | -------- | ------------- | -------- |
|FieldName|*Reserved*| Block MaxSize |*Reserved*|
In the tables, bit 7 is highest bit, while bit 0 is lowest.
__Version Number__
2-bits field, must be set to `01`.
Any other value cannot be decoded by this version of the specification.
Other version numbers will use different flag layouts.
__Block Independence flag__
If this flag is set to “1”, blocks are independent.
If this flag is set to “0”, each block depends on previous ones
(up to LZ4 window size, which is 64 KB).
In such case, it’s necessary to decode all blocks in sequence.
Block dependency improves compression ratio, especially for small blocks.
On the other hand, it makes random access or multi-threaded decoding impossible.
__Block checksum flag__
If this flag is set, each data block will be followed by a 4-bytes checksum,
calculated by using the xxHash-32 algorithm on the raw (compressed) data block.
The intention is to detect data corruption (storage or transmission errors)
immediately, before decoding.
Block checksum usage is optional.
__Content Size flag__
If this flag is set, the uncompressed size of data included within the frame
will be present as an 8 bytes unsigned little endian value, after the flags.
Content Size usage is optional.
__Content checksum flag__
If this flag is set, a 32-bits content checksum will be appended
after the EndMark.
__Dictionary ID flag__
If this flag is set, a 4-bytes Dict-ID field will be present,
after the descriptor flags and the Content Size.
__Block Maximum Size__
This information is useful to help the decoder allocate memory.
Size here refers to the original (uncompressed) data size.
Block Maximum Size is one value among the following table :
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| --- | --- | --- | --- | ----- | ------ | ---- | ---- |
| N/A | N/A | N/A | N/A | 64 KB | 256 KB | 1 MB | 4 MB |
The decoder may refuse to allocate block sizes above any system-specific size.
Unused values may be used in a future revision of the spec.
A decoder conformant with the current version of the spec
is only able to decode block sizes defined in this spec.
__Reserved bits__
Value of reserved bits **must** be 0 (zero).
Reserved bit might be used in a future version of the specification,
typically enabling new optional features.
When this happens, a decoder respecting the current specification version
shall not be able to decode such a frame.
__Content Size__
This is the original (uncompressed) size.
This information is optional, and only present if the associated flag is set.
Content size is provided using unsigned 8 Bytes, for a maximum of 16 Exabytes.
Format is Little endian.
This value is informational, typically for display or memory allocation.
It can be skipped by a decoder, or used to validate content correctness.
__Dictionary ID__
A dictionary is useful to compress short input sequences.
When present, the compressor can take advantage of dictionary's content
as a kind of “known prefix” to encode the input in a more compact manner.
When the frame descriptor defines independent blocks,
every block is initialized with the same dictionary.
If the frame descriptor defines linked blocks,
the dictionary is only used once, at the beginning of the frame.
The compressor and the decompressor must employ exactly the same dictionary for the data to be decodable.
The Dict-ID field is offered as a way to help the decoder determine
which dictionary must be used to correctly decode the compressed frame.
Dict-ID is only present if the associated flag is set.
It's an unsigned 32-bits value, stored using little-endian convention.
Within a single frame, only a single Dict-ID field can be defined.
Note that the Dict-ID field is optional.
Knowledge of which dictionary to employ can also be passed off-band,
for example, it could be implied by the context of the application.
__Header Checksum__
One-byte checksum of combined descriptor fields, including optional ones.
The value is the second byte of `xxh32()` : ` (xxh32()>>8) & 0xFF `
using zero as a seed, and the full Frame Descriptor as an input
(including optional fields when they are present).
A wrong checksum indicates that the descriptor is erroneous.
Data Blocks
-----------
| Block Size | data | (Block Checksum) |
|:----------:| ------ |:----------------:|
| 4 bytes | | 0 - 4 bytes |
__Block Size__
This field uses 4-bytes, format is little-endian.
If the highest bit is set (`1`), the block is uncompressed.
If the highest bit is not set (`0`), the block is LZ4-compressed,
using the [LZ4 block format specification](https://github.com/lz4/lz4/blob/dev/doc/lz4_Block_format.md).
All other bits give the size, in bytes, of the data section.
The size does not include the block checksum if present.
_Block_Size_ shall never be larger than _Block_Maximum_Size_.
Such an outcome could potentially happen for non-compressible sources.
In such a case, such data block **must** be passed using uncompressed format.
A value of `0x00000000` is invalid, and signifies an _EndMark_ instead.
Note that this is different from a value of `0x80000000` (highest bit set),
which is an uncompressed block of size 0 (empty),
which is valid, and therefore doesn't end a frame.
Note that, if _Block_checksum_ is enabled,
even an empty block must be followed by a 32-bit block checksum.
__Data__
Where the actual data to decode stands.
It might be compressed or not, depending on previous field indications.
When compressed, the data must respect the [LZ4 block format specification](https://github.com/lz4/lz4/blob/dev/doc/lz4_Block_format.md).
Note that a block is not necessarily full.
Uncompressed size of data can be any size __up to__ _Block_Maximum_Size_,
so it may contain less data than the maximum block size.
__Block checksum__
Only present if the associated flag is set.
This is a 4-bytes checksum value, in little endian format,
calculated by using the [xxHash-32 algorithm] on the __raw__ (undecoded) data block,
and a seed of zero.
The intention is to detect data corruption (storage or transmission errors)
before decoding.
_Block_checksum_ can be cumulative with _Content_checksum_.
[xxHash-32 algorithm]: https://github.com/Cyan4973/xxHash/blob/release/doc/xxhash_spec.md
Skippable Frames
----------------
| Magic Number | Frame Size | User Data |
|:------------:|:----------:| --------- |
| 4 bytes | 4 bytes | |
Skippable frames allow the integration of user-defined data
into a flow of concatenated frames.
Its design is pretty straightforward,
with the sole objective to allow the decoder to quickly skip
over user-defined data and continue decoding.
For the purpose of facilitating identification,
it is discouraged to start a flow of concatenated frames with a skippable frame.
If there is a need to start such a flow with some user data
encapsulated into a skippable frame,
it’s recommended to start with a zero-byte LZ4 frame
followed by a skippable frame.
This will make it easier for file type identifiers.
__Magic Number__
4 Bytes, Little endian format.
Value : 0x184D2A5X, which means any value from 0x184D2A50 to 0x184D2A5F.
All 16 values are valid to identify a skippable frame.
__Frame Size__
This is the size, in bytes, of the following User Data
(without including the magic number nor the size field itself).
4 Bytes, Little endian format, unsigned 32-bits.
This means User Data can’t be bigger than (2^32-1) Bytes.
__User Data__
User Data can be anything. Data will just be skipped by the decoder.
Legacy frame
------------
The Legacy frame format was defined into the initial versions of “LZ4Demo”.
Newer compressors should not use this format anymore, as it is too restrictive.
Main characteristics of the legacy format :
- Fixed block size : 8 MB.
- All blocks must be completely filled, except the last one.
- All blocks are always compressed, even when compression is detrimental.
- The last block is detected either because
it is followed by the “EOF” (End of File) mark,
or because it is followed by a known Frame Magic Number.
- No checksum
- Convention is Little endian
| MagicNb | B.CSize | CData | B.CSize | CData | (...) | EndMark |
| ------- | ------- | ----- | ------- | ----- | ------- | ------- |
| 4 bytes | 4 bytes | CSize | 4 bytes | CSize | x times | EOF |
__Magic Number__
4 Bytes, Little endian format.
Value : 0x184C2102
__Block Compressed Size__
This is the size, in bytes, of the following compressed data block.
4 Bytes, Little endian format.
__Data__
Where the actual compressed data stands.
Data is always compressed, even when compression is detrimental.
__EndMark__
End of legacy frame is implicit only.
It must be followed by a standard EOF (End Of File) signal,
whether it is a file or a stream.
Alternatively, if the frame is followed by a valid Frame Magic Number,
it is considered completed.
This policy makes it possible to concatenate legacy frames.
Any other value will be interpreted as a block size,
and trigger an error if it does not fit within acceptable range.
Version changes
---------------
1.6.4 : minor clarifications for Dictionaries
1.6.3 : minor : clarify Data Block
1.6.2 : clarifies specification of _EndMark_
1.6.1 : introduced terms "LZ4 Frame Header" and "LZ4 Frame Footer"
1.6.0 : restored Dictionary ID field in Frame header
1.5.1 : changed document format to MarkDown
1.5 : removed Dictionary ID from specification
1.4.1 : changed wording from “stream” to “frame”
1.4 : added skippable streams, re-added stream checksum
1.3 : modified header checksum
1.2 : reduced choice of “block size”, to postpone decision on “dynamic size of BlockSize Field”.
1.1 : optional fields are now part of the descriptor
1.0 : changed “block size” specification, adding a compressed/uncompressed flag
0.9 : reduced scale of “block maximum size” table
0.8 : removed : high compression flag
0.7 : removed : stream checksum
0.6 : settled : stream size uses 8 bytes, endian convention is little endian
0.5 : added copyright notice
0.4 : changed format to Google Doc compatible OpenDocument

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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>1.10.0 Manual</title>
</head>
<body>
<h1>1.10.0 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">Tuning memory usage</a></li>
<li><a href="#Chapter4">Simple Functions</a></li>
<li><a href="#Chapter5">Advanced Functions</a></li>
<li><a href="#Chapter6">Streaming Compression Functions</a></li>
<li><a href="#Chapter7">Streaming Decompression Functions</a></li>
<li><a href="#Chapter8">Experimental section</a></li>
<li><a href="#Chapter9">Private Definitions</a></li>
<li><a href="#Chapter10">Obsolete Functions</a></li>
</ol>
<hr>
<a name="Chapter1"></a><h2>Introduction</h2><pre>
LZ4 is lossless compression algorithm, providing compression speed >500 MB/s per core,
scalable with multi-cores CPU. It features an extremely fast decoder, with speed in
multiple GB/s per core, typically reaching RAM speed limits on multi-core systems.
The LZ4 compression library provides in-memory compression and decompression functions.
It gives full buffer control to user.
Compression can be done in:
- a single step (described as Simple Functions)
- a single step, reusing a context (described in Advanced Functions)
- unbounded multiple steps (described as Streaming compression)
lz4.h generates and decodes LZ4-compressed blocks (doc/lz4_Block_format.md).
Decompressing such a compressed block requires additional metadata.
Exact metadata depends on exact decompression function.
For the typical case of LZ4_decompress_safe(),
metadata includes block's compressed size, and maximum bound of decompressed size.
Each application is free to encode and pass such metadata in whichever way it wants.
lz4.h only handle blocks, it can not generate Frames.
Blocks are different from Frames (doc/lz4_Frame_format.md).
Frames bundle both blocks and metadata in a specified manner.
Embedding metadata is required for compressed data to be self-contained and portable.
Frame format is delivered through a companion API, declared in lz4frame.h.
The `lz4` CLI can only manage frames.
<BR></pre>
<pre><b>#if defined(LZ4_FREESTANDING) && (LZ4_FREESTANDING == 1)
# define LZ4_HEAPMODE 0
# define LZ4HC_HEAPMODE 0
# define LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION 1
# if !defined(LZ4_memcpy)
# error "LZ4_FREESTANDING requires macro 'LZ4_memcpy'."
# endif
# if !defined(LZ4_memset)
# error "LZ4_FREESTANDING requires macro 'LZ4_memset'."
# endif
# if !defined(LZ4_memmove)
# error "LZ4_FREESTANDING requires macro 'LZ4_memmove'."
# endif
#elif ! defined(LZ4_FREESTANDING)
# define LZ4_FREESTANDING 0
#endif
</b><p> When this macro is set to 1, it enables "freestanding mode" that is
suitable for typical freestanding environment which doesn't support
standard C library.
- LZ4_FREESTANDING is a compile-time switch.
- It requires the following macros to be defined:
LZ4_memcpy, LZ4_memmove, LZ4_memset.
- It only enables LZ4/HC functions which don't use heap.
All LZ4F_* functions are not supported.
- See tests/freestanding.c to check its basic setup.
</p></pre><BR>
<a name="Chapter2"></a><h2>Version</h2><pre></pre>
<pre><b>int LZ4_versionNumber (void); </b>/**< library version number; useful to check dll version; requires v1.3.0+ */<b>
</b></pre><BR>
<pre><b>const char* LZ4_versionString (void); </b>/**< library version string; useful to check dll version; requires v1.7.5+ */<b>
</b></pre><BR>
<a name="Chapter3"></a><h2>Tuning memory usage</h2><pre></pre>
<pre><b>#ifndef LZ4_MEMORY_USAGE
# define LZ4_MEMORY_USAGE LZ4_MEMORY_USAGE_DEFAULT
#endif
</b><p> Can be selected at compile time, by setting LZ4_MEMORY_USAGE.
Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB)
Increasing memory usage improves compression ratio, generally at the cost of speed.
Reduced memory usage may improve speed at the cost of ratio, thanks to better cache locality.
Default value is 14, for 16KB, which nicely fits into most L1 caches.
</p></pre><BR>
<a name="Chapter4"></a><h2>Simple Functions</h2><pre></pre>
<pre><b>int LZ4_compress_default(const char* src, char* dst, int srcSize, int dstCapacity);
</b><p> Compresses 'srcSize' bytes from buffer 'src'
into already allocated 'dst' buffer of size 'dstCapacity'.
Compression is guaranteed to succeed if 'dstCapacity' >= LZ4_compressBound(srcSize).
It also runs faster, so it's a recommended setting.
If the function cannot compress 'src' into a more limited 'dst' budget,
compression stops *immediately*, and the function result is zero.
In which case, 'dst' content is undefined (invalid).
srcSize : max supported value is LZ4_MAX_INPUT_SIZE.
dstCapacity : size of buffer 'dst' (which must be already allocated)
@return : the number of bytes written into buffer 'dst' (necessarily <= dstCapacity)
or 0 if compression fails
Note : This function is protected against buffer overflow scenarios (never writes outside 'dst' buffer, nor read outside 'source' buffer).
</p></pre><BR>
<pre><b>int LZ4_decompress_safe (const char* src, char* dst, int compressedSize, int dstCapacity);
</b><p> @compressedSize : is the exact complete size of the compressed block.
@dstCapacity : is the size of destination buffer (which must be already allocated),
presumed an upper bound of decompressed size.
@return : the number of bytes decompressed into destination buffer (necessarily <= dstCapacity)
If destination buffer is not large enough, decoding will stop and output an error code (negative value).
If the source stream is detected malformed, the function will stop decoding and return a negative result.
Note 1 : This function is protected against malicious data packets :
it will never writes outside 'dst' buffer, nor read outside 'source' buffer,
even if the compressed block is maliciously modified to order the decoder to do these actions.
In such case, the decoder stops immediately, and considers the compressed block malformed.
Note 2 : compressedSize and dstCapacity must be provided to the function, the compressed block does not contain them.
The implementation is free to send / store / derive this information in whichever way is most beneficial.
If there is a need for a different format which bundles together both compressed data and its metadata, consider looking at lz4frame.h instead.
</p></pre><BR>
<a name="Chapter5"></a><h2>Advanced Functions</h2><pre></pre>
<pre><b>int LZ4_compressBound(int inputSize);
</b><p> Provides the maximum size that LZ4 compression may output in a "worst case" scenario (input data not compressible)
This function is primarily useful for memory allocation purposes (destination buffer size).
Macro LZ4_COMPRESSBOUND() is also provided for compilation-time evaluation (stack memory allocation for example).
Note that LZ4_compress_default() compresses faster when dstCapacity is >= LZ4_compressBound(srcSize)
inputSize : max supported value is LZ4_MAX_INPUT_SIZE
return : maximum output size in a "worst case" scenario
or 0, if input size is incorrect (too large or negative)
</p></pre><BR>
<pre><b>int LZ4_compress_fast (const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
</b><p> Same as LZ4_compress_default(), but allows selection of "acceleration" factor.
The larger the acceleration value, the faster the algorithm, but also the lesser the compression.
It's a trade-off. It can be fine tuned, with each successive value providing roughly +~3% to speed.
An acceleration value of "1" is the same as regular LZ4_compress_default()
Values <= 0 will be replaced by LZ4_ACCELERATION_DEFAULT (currently == 1, see lz4.c).
Values > LZ4_ACCELERATION_MAX will be replaced by LZ4_ACCELERATION_MAX (currently == 65537, see lz4.c).
</p></pre><BR>
<pre><b>int LZ4_sizeofState(void);
int LZ4_compress_fast_extState (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
</b><p> Same as LZ4_compress_fast(), using an externally allocated memory space for its state.
Use LZ4_sizeofState() to know how much memory must be allocated,
and allocate it on 8-bytes boundaries (using `malloc()` typically).
Then, provide this buffer as `void* state` to compression function.
</p></pre><BR>
<pre><b>int LZ4_compress_destSize(const char* src, char* dst, int* srcSizePtr, int targetDstSize);
</b><p> Reverse the logic : compresses as much data as possible from 'src' buffer
into already allocated buffer 'dst', of size >= 'dstCapacity'.
This function either compresses the entire 'src' content into 'dst' if it's large enough,
or fill 'dst' buffer completely with as much data as possible from 'src'.
note: acceleration parameter is fixed to "default".
*srcSizePtr : in+out parameter. Initially contains size of input.
Will be modified to indicate how many bytes where read from 'src' to fill 'dst'.
New value is necessarily <= input value.
@return : Nb bytes written into 'dst' (necessarily <= dstCapacity)
or 0 if compression fails.
Note : 'targetDstSize' must be >= 1, because it's the smallest valid lz4 payload.
Note 2:from v1.8.2 to v1.9.1, this function had a bug (fixed in v1.9.2+):
the produced compressed content could, in rare circumstances,
require to be decompressed into a destination buffer
larger by at least 1 byte than decompressesSize.
If an application uses `LZ4_compress_destSize()`,
it's highly recommended to update liblz4 to v1.9.2 or better.
If this can't be done or ensured,
the receiving decompression function should provide
a dstCapacity which is > decompressedSize, by at least 1 byte.
See https://github.com/lz4/lz4/issues/859 for details
</p></pre><BR>
<pre><b>int LZ4_decompress_safe_partial (const char* src, char* dst, int srcSize, int targetOutputSize, int dstCapacity);
</b><p> Decompress an LZ4 compressed block, of size 'srcSize' at position 'src',
into destination buffer 'dst' of size 'dstCapacity'.
Up to 'targetOutputSize' bytes will be decoded.
The function stops decoding on reaching this objective.
This can be useful to boost performance
whenever only the beginning of a block is required.
@return : the number of bytes decoded in `dst` (necessarily <= targetOutputSize)
If source stream is detected malformed, function returns a negative result.
Note 1 : @return can be < targetOutputSize, if compressed block contains less data.
Note 2 : targetOutputSize must be <= dstCapacity
Note 3 : this function effectively stops decoding on reaching targetOutputSize,
so dstCapacity is kind of redundant.
This is because in older versions of this function,
decoding operation would still write complete sequences.
Therefore, there was no guarantee that it would stop writing at exactly targetOutputSize,
it could write more bytes, though only up to dstCapacity.
Some "margin" used to be required for this operation to work properly.
Thankfully, this is no longer necessary.
The function nonetheless keeps the same signature, in an effort to preserve API compatibility.
Note 4 : If srcSize is the exact size of the block,
then targetOutputSize can be any value,
including larger than the block's decompressed size.
The function will, at most, generate block's decompressed size.
Note 5 : If srcSize is _larger_ than block's compressed size,
then targetOutputSize **MUST** be <= block's decompressed size.
Otherwise, *silent corruption will occur*.
</p></pre><BR>
<a name="Chapter6"></a><h2>Streaming Compression Functions</h2><pre></pre>
<pre><b>#if !defined(RC_INVOKED) </b>/* https://docs.microsoft.com/en-us/windows/win32/menurc/predefined-macros */<b>
#if !defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION)
LZ4_stream_t* LZ4_createStream(void);
int LZ4_freeStream (LZ4_stream_t* streamPtr);
#endif </b>/* !defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION) */<b>
#endif
</b><p>
- RC_INVOKED is predefined symbol of rc.exe (the resource compiler which is part of MSVC/Visual Studio).
https://docs.microsoft.com/en-us/windows/win32/menurc/predefined-macros
- Since rc.exe is a legacy compiler, it truncates long symbol (> 30 chars)
and reports warning "RC4011: identifier truncated".
- To eliminate the warning, we surround long preprocessor symbol with
"#if !defined(RC_INVOKED) ... #endif" block that means
"skip this block when rc.exe is trying to read it".
</p></pre><BR>
<pre><b>void LZ4_resetStream_fast (LZ4_stream_t* streamPtr);
</b><p> Use this to prepare an LZ4_stream_t for a new chain of dependent blocks
(e.g., LZ4_compress_fast_continue()).
An LZ4_stream_t must be initialized once before usage.
This is automatically done when created by LZ4_createStream().
However, should the LZ4_stream_t be simply declared on stack (for example),
it's necessary to initialize it first, using LZ4_initStream().
After init, start any new stream with LZ4_resetStream_fast().
A same LZ4_stream_t can be re-used multiple times consecutively
and compress multiple streams,
provided that it starts each new stream with LZ4_resetStream_fast().
LZ4_resetStream_fast() is much faster than LZ4_initStream(),
but is not compatible with memory regions containing garbage data.
Note: it's only useful to call LZ4_resetStream_fast()
in the context of streaming compression.
The *extState* functions perform their own resets.
Invoking LZ4_resetStream_fast() before is redundant, and even counterproductive.
</p></pre><BR>
<pre><b>int LZ4_loadDict (LZ4_stream_t* streamPtr, const char* dictionary, int dictSize);
</b><p> Use this function to reference a static dictionary into LZ4_stream_t.
The dictionary must remain available during compression.
LZ4_loadDict() triggers a reset, so any previous data will be forgotten.
The same dictionary will have to be loaded on decompression side for successful decoding.
Dictionary are useful for better compression of small data (KB range).
While LZ4 itself accepts any input as dictionary, dictionary efficiency is also a topic.
When in doubt, employ the Zstandard's Dictionary Builder.
Loading a size of 0 is allowed, and is the same as reset.
@return : loaded dictionary size, in bytes (note: only the last 64 KB are loaded)
</p></pre><BR>
<pre><b>int LZ4_loadDictSlow(LZ4_stream_t* streamPtr, const char* dictionary, int dictSize);
</b><p> Same as LZ4_loadDict(),
but uses a bit more cpu to reference the dictionary content more thoroughly.
This is expected to slightly improve compression ratio.
The extra-cpu cost is likely worth it if the dictionary is re-used across multiple sessions.
@return : loaded dictionary size, in bytes (note: only the last 64 KB are loaded)
</p></pre><BR>
<pre><b>void
LZ4_attach_dictionary(LZ4_stream_t* workingStream,
const LZ4_stream_t* dictionaryStream);
</b><p>
This allows efficient re-use of a static dictionary multiple times.
Rather than re-loading the dictionary buffer into a working context before
each compression, or copying a pre-loaded dictionary's LZ4_stream_t into a
working LZ4_stream_t, this function introduces a no-copy setup mechanism,
in which the working stream references @dictionaryStream in-place.
Several assumptions are made about the state of @dictionaryStream.
Currently, only states which have been prepared by LZ4_loadDict() or
LZ4_loadDictSlow() should be expected to work.
Alternatively, the provided @dictionaryStream may be NULL,
in which case any existing dictionary stream is unset.
If a dictionary is provided, it replaces any pre-existing stream history.
The dictionary contents are the only history that can be referenced and
logically immediately precede the data compressed in the first subsequent
compression call.
The dictionary will only remain attached to the working stream through the
first compression call, at the end of which it is cleared.
@dictionaryStream stream (and source buffer) must remain in-place / accessible / unchanged
through the completion of the compression session.
Note: there is no equivalent LZ4_attach_*() method on the decompression side
because there is no initialization cost, hence no need to share the cost across multiple sessions.
To decompress LZ4 blocks using dictionary, attached or not,
just employ the regular LZ4_setStreamDecode() for streaming,
or the stateless LZ4_decompress_safe_usingDict() for one-shot decompression.
</p></pre><BR>
<pre><b>int LZ4_compress_fast_continue (LZ4_stream_t* streamPtr, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
</b><p> Compress 'src' content using data from previously compressed blocks, for better compression ratio.
'dst' buffer must be already allocated.
If dstCapacity >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster.
@return : size of compressed block
or 0 if there is an error (typically, cannot fit into 'dst').
Note 1 : Each invocation to LZ4_compress_fast_continue() generates a new block.
Each block has precise boundaries.
Each block must be decompressed separately, calling LZ4_decompress_*() with relevant metadata.
It's not possible to append blocks together and expect a single invocation of LZ4_decompress_*() to decompress them together.
Note 2 : The previous 64KB of source data is __assumed__ to remain present, unmodified, at same address in memory !
Note 3 : When input is structured as a double-buffer, each buffer can have any size, including < 64 KB.
Make sure that buffers are separated, by at least one byte.
This construction ensures that each block only depends on previous block.
Note 4 : If input buffer is a ring-buffer, it can have any size, including < 64 KB.
Note 5 : After an error, the stream status is undefined (invalid), it can only be reset or freed.
</p></pre><BR>
<pre><b>int LZ4_saveDict (LZ4_stream_t* streamPtr, char* safeBuffer, int maxDictSize);
</b><p> If last 64KB data cannot be guaranteed to remain available at its current memory location,
save it into a safer place (char* safeBuffer).
This is schematically equivalent to a memcpy() followed by LZ4_loadDict(),
but is much faster, because LZ4_saveDict() doesn't need to rebuild tables.
@return : saved dictionary size in bytes (necessarily <= maxDictSize), or 0 if error.
</p></pre><BR>
<a name="Chapter7"></a><h2>Streaming Decompression Functions</h2><pre> Bufferless synchronous API
<BR></pre>
<pre><b>#if !defined(RC_INVOKED) </b>/* https://docs.microsoft.com/en-us/windows/win32/menurc/predefined-macros */<b>
#if !defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION)
LZ4_streamDecode_t* LZ4_createStreamDecode(void);
int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream);
#endif </b>/* !defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION) */<b>
#endif
</b><p> creation / destruction of streaming decompression tracking context.
A tracking context can be re-used multiple times.
</p></pre><BR>
<pre><b>int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dictionary, int dictSize);
</b><p> An LZ4_streamDecode_t context can be allocated once and re-used multiple times.
Use this function to start decompression of a new stream of blocks.
A dictionary can optionally be set. Use NULL or size 0 for a reset order.
Dictionary is presumed stable : it must remain accessible and unmodified during next decompression.
@return : 1 if OK, 0 if error
</p></pre><BR>
<pre><b>int LZ4_decoderRingBufferSize(int maxBlockSize);
#define LZ4_DECODER_RING_BUFFER_SIZE(maxBlockSize) (65536 + 14 + (maxBlockSize)) </b>/* for static allocation; maxBlockSize presumed valid */<b>
</b><p> Note : in a ring buffer scenario (optional),
blocks are presumed decompressed next to each other
up to the moment there is not enough remaining space for next block (remainingSize < maxBlockSize),
at which stage it resumes from beginning of ring buffer.
When setting such a ring buffer for streaming decompression,
provides the minimum size of this ring buffer
to be compatible with any source respecting maxBlockSize condition.
@return : minimum ring buffer size,
or 0 if there is an error (invalid maxBlockSize).
</p></pre><BR>
<pre><b>int
LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode,
const char* src, char* dst,
int srcSize, int dstCapacity);
</b><p> This decoding function allows decompression of consecutive blocks in "streaming" mode.
The difference with the usual independent blocks is that
new blocks are allowed to find references into former blocks.
A block is an unsplittable entity, and must be presented entirely to the decompression function.
LZ4_decompress_safe_continue() only accepts one block at a time.
It's modeled after `LZ4_decompress_safe()` and behaves similarly.
@LZ4_streamDecode : decompression state, tracking the position in memory of past data
@compressedSize : exact complete size of one compressed block.
@dstCapacity : size of destination buffer (which must be already allocated),
must be an upper bound of decompressed size.
@return : number of bytes decompressed into destination buffer (necessarily <= dstCapacity)
If destination buffer is not large enough, decoding will stop and output an error code (negative value).
If the source stream is detected malformed, the function will stop decoding and return a negative result.
The last 64KB of previously decoded data *must* remain available and unmodified
at the memory position where they were previously decoded.
If less than 64KB of data has been decoded, all the data must be present.
Special : if decompression side sets a ring buffer, it must respect one of the following conditions :
- Decompression buffer size is _at least_ LZ4_decoderRingBufferSize(maxBlockSize).
maxBlockSize is the maximum size of any single block. It can have any value > 16 bytes.
In which case, encoding and decoding buffers do not need to be synchronized.
Actually, data can be produced by any source compliant with LZ4 format specification, and respecting maxBlockSize.
- Synchronized mode :
Decompression buffer size is _exactly_ the same as compression buffer size,
and follows exactly same update rule (block boundaries at same positions),
and decoding function is provided with exact decompressed size of each block (exception for last block of the stream),
_then_ decoding & encoding ring buffer can have any size, including small ones ( < 64 KB).
- Decompression buffer is larger than encoding buffer, by a minimum of maxBlockSize more bytes.
In which case, encoding and decoding buffers do not need to be synchronized,
and encoding ring buffer can have any size, including small ones ( < 64 KB).
Whenever these conditions are not possible,
save the last 64KB of decoded data into a safe buffer where it can't be modified during decompression,
then indicate where this data is saved using LZ4_setStreamDecode(), before decompressing next block.
</p></pre><BR>
<pre><b>int
LZ4_decompress_safe_usingDict(const char* src, char* dst,
int srcSize, int dstCapacity,
const char* dictStart, int dictSize);
</b><p> Works the same as
a combination of LZ4_setStreamDecode() followed by LZ4_decompress_safe_continue()
However, it's stateless: it doesn't need any LZ4_streamDecode_t state.
Dictionary is presumed stable : it must remain accessible and unmodified during decompression.
Performance tip : Decompression speed can be substantially increased
when dst == dictStart + dictSize.
</p></pre><BR>
<pre><b>int
LZ4_decompress_safe_partial_usingDict(const char* src, char* dst,
int compressedSize,
int targetOutputSize, int maxOutputSize,
const char* dictStart, int dictSize);
</b><p> Behaves the same as LZ4_decompress_safe_partial()
with the added ability to specify a memory segment for past data.
Performance tip : Decompression speed can be substantially increased
when dst == dictStart + dictSize.
</p></pre><BR>
<a name="Chapter8"></a><h2>Experimental section</h2><pre>
Symbols declared in this section must be considered unstable. Their
signatures or semantics may change, or they may be removed altogether in the
future. They are therefore only safe to depend on when the caller is
statically linked against the library.
To protect against unsafe usage, not only are the declarations guarded,
the definitions are hidden by default
when building LZ4 as a shared/dynamic library.
In order to access these declarations,
define LZ4_STATIC_LINKING_ONLY in your application
before including LZ4's headers.
In order to make their implementations accessible dynamically, you must
define LZ4_PUBLISH_STATIC_FUNCTIONS when building the LZ4 library.
<BR></pre>
<pre><b>LZ4LIB_STATIC_API int LZ4_compress_fast_extState_fastReset (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
</b><p> A variant of LZ4_compress_fast_extState().
Using this variant avoids an expensive initialization step.
It is only safe to call if the state buffer is known to be correctly initialized already
(see above comment on LZ4_resetStream_fast() for a definition of "correctly initialized").
From a high level, the difference is that
this function initializes the provided state with a call to something like LZ4_resetStream_fast()
while LZ4_compress_fast_extState() starts with a call to LZ4_resetStream().
</p></pre><BR>
<pre><b>int LZ4_compress_destSize_extState(void* state, const char* src, char* dst, int* srcSizePtr, int targetDstSize, int acceleration);
</b><p> Same as LZ4_compress_destSize(), but using an externally allocated state.
Also: exposes @acceleration
</p></pre><BR>
<pre><b></b><p>
It's possible to have input and output sharing the same buffer,
for highly constrained memory environments.
In both cases, it requires input to lay at the end of the buffer,
and decompression to start at beginning of the buffer.
Buffer size must feature some margin, hence be larger than final size.
|<------------------------buffer--------------------------------->|
|<-----------compressed data--------->|
|<-----------decompressed size------------------>|
|<----margin---->|
This technique is more useful for decompression,
since decompressed size is typically larger,
and margin is short.
In-place decompression will work inside any buffer
which size is >= LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize).
This presumes that decompressedSize > compressedSize.
Otherwise, it means compression actually expanded data,
and it would be more efficient to store such data with a flag indicating it's not compressed.
This can happen when data is not compressible (already compressed, or encrypted).
For in-place compression, margin is larger, as it must be able to cope with both
history preservation, requiring input data to remain unmodified up to LZ4_DISTANCE_MAX,
and data expansion, which can happen when input is not compressible.
As a consequence, buffer size requirements are much higher,
and memory savings offered by in-place compression are more limited.
There are ways to limit this cost for compression :
- Reduce history size, by modifying LZ4_DISTANCE_MAX.
Note that it is a compile-time constant, so all compressions will apply this limit.
Lower values will reduce compression ratio, except when input_size < LZ4_DISTANCE_MAX,
so it's a reasonable trick when inputs are known to be small.
- Require the compressor to deliver a "maximum compressed size".
This is the `dstCapacity` parameter in `LZ4_compress*()`.
When this size is < LZ4_COMPRESSBOUND(inputSize), then compression can fail,
in which case, the return code will be 0 (zero).
The caller must be ready for these cases to happen,
and typically design a backup scheme to send data uncompressed.
The combination of both techniques can significantly reduce
the amount of margin required for in-place compression.
In-place compression can work in any buffer
which size is >= (maxCompressedSize)
with maxCompressedSize == LZ4_COMPRESSBOUND(srcSize) for guaranteed compression success.
LZ4_COMPRESS_INPLACE_BUFFER_SIZE() depends on both maxCompressedSize and LZ4_DISTANCE_MAX,
so it's possible to reduce memory requirements by playing with them.
</p></pre><BR>
<pre><b>#define LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize) ((decompressedSize) + LZ4_DECOMPRESS_INPLACE_MARGIN(decompressedSize)) </b>/**< note: presumes that compressedSize < decompressedSize. note2: margin is overestimated a bit, since it could use compressedSize instead */<b>
</b></pre><BR>
<pre><b>#define LZ4_COMPRESS_INPLACE_BUFFER_SIZE(maxCompressedSize) ((maxCompressedSize) + LZ4_COMPRESS_INPLACE_MARGIN) </b>/**< maxCompressedSize is generally LZ4_COMPRESSBOUND(inputSize), but can be set to any lower value, with the risk that compression can fail (return code 0(zero)) */<b>
</b></pre><BR>
<a name="Chapter9"></a><h2>Private Definitions</h2><pre>
Do not use these definitions directly.
They are only exposed to allow static allocation of `LZ4_stream_t` and `LZ4_streamDecode_t`.
Accessing members will expose user code to API and/or ABI break in future versions of the library.
<BR></pre>
<pre><b></b><p> Never ever use below internal definitions directly !
These definitions are not API/ABI safe, and may change in future versions.
If you need static allocation, declare or allocate an LZ4_stream_t object.
</p></pre><BR>
<pre><b>LZ4_stream_t* LZ4_initStream (void* stateBuffer, size_t size);
</b><p> An LZ4_stream_t structure must be initialized at least once.
This is automatically done when invoking LZ4_createStream(),
but it's not when the structure is simply declared on stack (for example).
Use LZ4_initStream() to properly initialize a newly declared LZ4_stream_t.
It can also initialize any arbitrary buffer of sufficient size,
and will @return a pointer of proper type upon initialization.
Note : initialization fails if size and alignment conditions are not respected.
In which case, the function will @return NULL.
Note2: An LZ4_stream_t structure guarantees correct alignment and size.
Note3: Before v1.9.0, use LZ4_resetStream() instead
</p></pre><BR>
<pre><b>typedef struct {
const LZ4_byte* externalDict;
const LZ4_byte* prefixEnd;
size_t extDictSize;
size_t prefixSize;
} LZ4_streamDecode_t_internal;
</b><p> Never ever use below internal definitions directly !
These definitions are not API/ABI safe, and may change in future versions.
If you need static allocation, declare or allocate an LZ4_streamDecode_t object.
</p></pre><BR>
<a name="Chapter10"></a><h2>Obsolete Functions</h2><pre></pre>
<pre><b>#ifdef LZ4_DISABLE_DEPRECATE_WARNINGS
# define LZ4_DEPRECATED(message) </b>/* disable deprecation warnings */<b>
#else
# if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b>
# define LZ4_DEPRECATED(message) [[deprecated(message)]]
# elif defined(_MSC_VER)
# define LZ4_DEPRECATED(message) __declspec(deprecated(message))
# elif defined(__clang__) || (defined(__GNUC__) && (__GNUC__ * 10 + __GNUC_MINOR__ >= 45))
# define LZ4_DEPRECATED(message) __attribute__((deprecated(message)))
# elif defined(__GNUC__) && (__GNUC__ * 10 + __GNUC_MINOR__ >= 31)
# define LZ4_DEPRECATED(message) __attribute__((deprecated))
# else
# pragma message("WARNING: LZ4_DEPRECATED needs custom implementation for this compiler")
# define LZ4_DEPRECATED(message) </b>/* disabled */<b>
# endif
#endif </b>/* LZ4_DISABLE_DEPRECATE_WARNINGS */<b>
</b><p>
Deprecated functions make the compiler generate a warning when invoked.
This is meant to invite users to update their source code.
Should deprecation warnings be a problem, it is generally possible to disable them,
typically with -Wno-deprecated-declarations for gcc
or _CRT_SECURE_NO_WARNINGS in Visual.
Another method is to define LZ4_DISABLE_DEPRECATE_WARNINGS
before including the header file.
</p></pre><BR>
<pre><b>LZ4_DEPRECATED("use LZ4_compress_default() instead") LZ4LIB_API int LZ4_compress (const char* src, char* dest, int srcSize);
LZ4_DEPRECATED("use LZ4_compress_default() instead") LZ4LIB_API int LZ4_compress_limitedOutput (const char* src, char* dest, int srcSize, int maxOutputSize);
LZ4_DEPRECATED("use LZ4_compress_fast_extState() instead") LZ4LIB_API int LZ4_compress_withState (void* state, const char* source, char* dest, int inputSize);
LZ4_DEPRECATED("use LZ4_compress_fast_extState() instead") LZ4LIB_API int LZ4_compress_limitedOutput_withState (void* state, const char* source, char* dest, int inputSize, int maxOutputSize);
LZ4_DEPRECATED("use LZ4_compress_fast_continue() instead") LZ4LIB_API int LZ4_compress_continue (LZ4_stream_t* LZ4_streamPtr, const char* source, char* dest, int inputSize);
LZ4_DEPRECATED("use LZ4_compress_fast_continue() instead") LZ4LIB_API int LZ4_compress_limitedOutput_continue (LZ4_stream_t* LZ4_streamPtr, const char* source, char* dest, int inputSize, int maxOutputSize);
</b><p></p></pre><BR>
<pre><b>LZ4_DEPRECATED("use LZ4_decompress_fast() instead") LZ4LIB_API int LZ4_uncompress (const char* source, char* dest, int outputSize);
LZ4_DEPRECATED("use LZ4_decompress_safe() instead") LZ4LIB_API int LZ4_uncompress_unknownOutputSize (const char* source, char* dest, int isize, int maxOutputSize);
</b><p></p></pre><BR>
<pre><b>LZ4_DEPRECATED("use LZ4_decompress_safe_usingDict() instead") LZ4LIB_API int LZ4_decompress_safe_withPrefix64k (const char* src, char* dst, int compressedSize, int maxDstSize);
LZ4_DEPRECATED("use LZ4_decompress_fast_usingDict() instead") LZ4LIB_API int LZ4_decompress_fast_withPrefix64k (const char* src, char* dst, int originalSize);
</b><p></p></pre><BR>
<pre><b>LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_partial() instead")
int LZ4_decompress_fast (const char* src, char* dst, int originalSize);
LZ4_DEPRECATED("This function is deprecated and unsafe. Consider migrating towards LZ4_decompress_safe_continue() instead. "
"Note that the contract will change (requires block's compressed size, instead of decompressed size)")
int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int originalSize);
LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_partial_usingDict() instead")
int LZ4_decompress_fast_usingDict (const char* src, char* dst, int originalSize, const char* dictStart, int dictSize);
</b><p> These functions used to be faster than LZ4_decompress_safe(),
but this is no longer the case. They are now slower.
This is because LZ4_decompress_fast() doesn't know the input size,
and therefore must progress more cautiously into the input buffer to not read beyond the end of block.
On top of that `LZ4_decompress_fast()` is not protected vs malformed or malicious inputs, making it a security liability.
As a consequence, LZ4_decompress_fast() is strongly discouraged, and deprecated.
The last remaining LZ4_decompress_fast() specificity is that
it can decompress a block without knowing its compressed size.
Such functionality can be achieved in a more secure manner
by employing LZ4_decompress_safe_partial().
Parameters:
originalSize : is the uncompressed size to regenerate.
`dst` must be already allocated, its size must be >= 'originalSize' bytes.
@return : number of bytes read from source buffer (== compressed size).
The function expects to finish at block's end exactly.
If the source stream is detected malformed, the function stops decoding and returns a negative result.
note : LZ4_decompress_fast*() requires originalSize. Thanks to this information, it never writes past the output buffer.
However, since it doesn't know its 'src' size, it may read an unknown amount of input, past input buffer bounds.
Also, since match offsets are not validated, match reads from 'src' may underflow too.
These issues never happen if input (compressed) data is correct.
But they may happen if input data is invalid (error or intentional tampering).
As a consequence, use these functions in trusted environments with trusted data **only**.
</p></pre><BR>
<pre><b>void LZ4_resetStream (LZ4_stream_t* streamPtr);
</b><p> An LZ4_stream_t structure must be initialized at least once.
This is done with LZ4_initStream(), or LZ4_resetStream().
Consider switching to LZ4_initStream(),
invoking LZ4_resetStream() will trigger deprecation warnings in the future.
</p></pre><BR>
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<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>1.10.0 Manual</title>
</head>
<body>
<h1>1.10.0 Manual</h1>
<hr>
<a name="Contents"></a><h2>Contents</h2>
<ol>
<li><a href="#Chapter1">Introduction</a></li>
<li><a href="#Chapter2">Compiler specifics</a></li>
<li><a href="#Chapter3">Error management</a></li>
<li><a href="#Chapter4">Frame compression types</a></li>
<li><a href="#Chapter5">Simple compression function</a></li>
<li><a href="#Chapter6">Advanced compression functions</a></li>
<li><a href="#Chapter7">Resource Management</a></li>
<li><a href="#Chapter8">Compression</a></li>
<li><a href="#Chapter9">Decompression functions</a></li>
<li><a href="#Chapter10">Streaming decompression functions</a></li>
<li><a href="#Chapter11">Dictionary compression API</a></li>
<li><a href="#Chapter12">Bulk processing dictionary compression</a></li>
<li><a href="#Chapter13">Advanced compression operations</a></li>
<li><a href="#Chapter14">Custom memory allocation</a></li>
</ol>
<hr>
<a name="Chapter1"></a><h2>Introduction</h2><pre>
lz4frame.h implements LZ4 frame specification: see doc/lz4_Frame_format.md .
LZ4 Frames are compatible with `lz4` CLI,
and designed to be interoperable with any system.
<BR></pre>
<a name="Chapter2"></a><h2>Compiler specifics</h2><pre></pre>
<a name="Chapter3"></a><h2>Error management</h2><pre></pre>
<pre><b>unsigned LZ4F_isError(LZ4F_errorCode_t code); </b>/**< tells when a function result is an error code */<b>
</b></pre><BR>
<pre><b>const char* LZ4F_getErrorName(LZ4F_errorCode_t code); </b>/**< return error code string; for debugging */<b>
</b></pre><BR>
<a name="Chapter4"></a><h2>Frame compression types</h2><pre>
<BR></pre>
<pre><b>typedef enum {
LZ4F_default=0,
LZ4F_max64KB=4,
LZ4F_max256KB=5,
LZ4F_max1MB=6,
LZ4F_max4MB=7
LZ4F_OBSOLETE_ENUM(max64KB)
LZ4F_OBSOLETE_ENUM(max256KB)
LZ4F_OBSOLETE_ENUM(max1MB)
LZ4F_OBSOLETE_ENUM(max4MB)
} LZ4F_blockSizeID_t;
</b></pre><BR>
<pre><b>typedef enum {
LZ4F_blockLinked=0,
LZ4F_blockIndependent
LZ4F_OBSOLETE_ENUM(blockLinked)
LZ4F_OBSOLETE_ENUM(blockIndependent)
} LZ4F_blockMode_t;
</b></pre><BR>
<pre><b>typedef enum {
LZ4F_noContentChecksum=0,
LZ4F_contentChecksumEnabled
LZ4F_OBSOLETE_ENUM(noContentChecksum)
LZ4F_OBSOLETE_ENUM(contentChecksumEnabled)
} LZ4F_contentChecksum_t;
</b></pre><BR>
<pre><b>typedef enum {
LZ4F_noBlockChecksum=0,
LZ4F_blockChecksumEnabled
} LZ4F_blockChecksum_t;
</b></pre><BR>
<pre><b>typedef enum {
LZ4F_frame=0,
LZ4F_skippableFrame
LZ4F_OBSOLETE_ENUM(skippableFrame)
} LZ4F_frameType_t;
</b></pre><BR>
<pre><b>typedef struct {
LZ4F_blockSizeID_t blockSizeID; </b>/* max64KB, max256KB, max1MB, max4MB; 0 == default (LZ4F_max64KB) */<b>
LZ4F_blockMode_t blockMode; </b>/* LZ4F_blockLinked, LZ4F_blockIndependent; 0 == default (LZ4F_blockLinked) */<b>
LZ4F_contentChecksum_t contentChecksumFlag; </b>/* 1: add a 32-bit checksum of frame's decompressed data; 0 == default (disabled) */<b>
LZ4F_frameType_t frameType; </b>/* read-only field : LZ4F_frame or LZ4F_skippableFrame */<b>
unsigned long long contentSize; </b>/* Size of uncompressed content ; 0 == unknown */<b>
unsigned dictID; </b>/* Dictionary ID, sent by compressor to help decoder select correct dictionary; 0 == no dictID provided */<b>
LZ4F_blockChecksum_t blockChecksumFlag; </b>/* 1: each block followed by a checksum of block's compressed data; 0 == default (disabled) */<b>
} LZ4F_frameInfo_t;
</b><p> makes it possible to set or read frame parameters.
Structure must be first init to 0, using memset() or LZ4F_INIT_FRAMEINFO,
setting all parameters to default.
It's then possible to update selectively some parameters
</p></pre><BR>
<pre><b>typedef struct {
LZ4F_frameInfo_t frameInfo;
int compressionLevel; </b>/* 0: default (fast mode); values > LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values < 0 trigger "fast acceleration" */<b>
unsigned autoFlush; </b>/* 1: always flush; reduces usage of internal buffers */<b>
unsigned favorDecSpeed; </b>/* 1: parser favors decompression speed vs compression ratio. Only works for high compression modes (>= LZ4HC_CLEVEL_OPT_MIN) */ /* v1.8.2+ */<b>
unsigned reserved[3]; </b>/* must be zero for forward compatibility */<b>
} LZ4F_preferences_t;
</b><p> makes it possible to supply advanced compression instructions to streaming interface.
Structure must be first init to 0, using memset() or LZ4F_INIT_PREFERENCES,
setting all parameters to default.
All reserved fields must be set to zero.
</p></pre><BR>
<a name="Chapter5"></a><h2>Simple compression function</h2><pre></pre>
<pre><b>size_t LZ4F_compressFrame(void* dstBuffer, size_t dstCapacity,
const void* srcBuffer, size_t srcSize,
const LZ4F_preferences_t* preferencesPtr);
</b><p> Compress srcBuffer content into an LZ4-compressed frame.
It's a one shot operation, all input content is consumed, and all output is generated.
Note : it's a stateless operation (no LZ4F_cctx state needed).
In order to reduce load on the allocator, LZ4F_compressFrame(), by default,
uses the stack to allocate space for the compression state and some table.
If this usage of the stack is too much for your application,
consider compiling `lz4frame.c` with compile-time macro LZ4F_HEAPMODE set to 1 instead.
All state allocations will use the Heap.
It also means each invocation of LZ4F_compressFrame() will trigger several internal alloc/free invocations.
@dstCapacity MUST be >= LZ4F_compressFrameBound(srcSize, preferencesPtr).
@preferencesPtr is optional : one can provide NULL, in which case all preferences are set to default.
@return : number of bytes written into dstBuffer.
or an error code if it fails (can be tested using LZ4F_isError())
</p></pre><BR>
<pre><b>size_t LZ4F_compressFrameBound(size_t srcSize, const LZ4F_preferences_t* preferencesPtr);
</b><p> Returns the maximum possible compressed size with LZ4F_compressFrame() given srcSize and preferences.
`preferencesPtr` is optional. It can be replaced by NULL, in which case, the function will assume default preferences.
Note : this result is only usable with LZ4F_compressFrame().
It may also be relevant to LZ4F_compressUpdate() _only if_ no flush() operation is ever performed.
</p></pre><BR>
<pre><b>int LZ4F_compressionLevel_max(void); </b>/* v1.8.0+ */<b>
</b><p> @return maximum allowed compression level (currently: 12)
</p></pre><BR>
<a name="Chapter6"></a><h2>Advanced compression functions</h2><pre></pre>
<pre><b>typedef struct {
unsigned stableSrc; </b>/* 1 == src content will remain present on future calls to LZ4F_compress(); skip copying src content within tmp buffer */<b>
unsigned reserved[3];
} LZ4F_compressOptions_t;
</b></pre><BR>
<a name="Chapter7"></a><h2>Resource Management</h2><pre></pre>
<pre><b>LZ4F_errorCode_t LZ4F_createCompressionContext(LZ4F_cctx** cctxPtr, unsigned version);
LZ4F_errorCode_t LZ4F_freeCompressionContext(LZ4F_cctx* cctx);
</b><p> The first thing to do is to create a compressionContext object,
which will keep track of operation state during streaming compression.
This is achieved using LZ4F_createCompressionContext(), which takes as argument a version,
and a pointer to LZ4F_cctx*, to write the resulting pointer into.
@version provided MUST be LZ4F_VERSION. It is intended to track potential version mismatch, notably when using DLL.
The function provides a pointer to a fully allocated LZ4F_cctx object.
@cctxPtr MUST be != NULL.
If @return != zero, context creation failed.
A created compression context can be employed multiple times for consecutive streaming operations.
Once all streaming compression jobs are completed,
the state object can be released using LZ4F_freeCompressionContext().
Note1 : LZ4F_freeCompressionContext() is always successful. Its return value can be ignored.
Note2 : LZ4F_freeCompressionContext() works fine with NULL input pointers (do nothing).
</p></pre><BR>
<a name="Chapter8"></a><h2>Compression</h2><pre></pre>
<pre><b>size_t LZ4F_compressBegin(LZ4F_cctx* cctx,
void* dstBuffer, size_t dstCapacity,
const LZ4F_preferences_t* prefsPtr);
</b><p> will write the frame header into dstBuffer.
dstCapacity must be >= LZ4F_HEADER_SIZE_MAX bytes.
`prefsPtr` is optional : NULL can be provided to set all preferences to default.
@return : number of bytes written into dstBuffer for the header
or an error code (which can be tested using LZ4F_isError())
</p></pre><BR>
<pre><b>size_t LZ4F_compressBound(size_t srcSize, const LZ4F_preferences_t* prefsPtr);
</b><p> Provides minimum dstCapacity required to guarantee success of
LZ4F_compressUpdate(), given a srcSize and preferences, for a worst case scenario.
When srcSize==0, LZ4F_compressBound() provides an upper bound for LZ4F_flush() and LZ4F_compressEnd() instead.
Note that the result is only valid for a single invocation of LZ4F_compressUpdate().
When invoking LZ4F_compressUpdate() multiple times,
if the output buffer is gradually filled up instead of emptied and re-used from its start,
one must check if there is enough remaining capacity before each invocation, using LZ4F_compressBound().
@return is always the same for a srcSize and prefsPtr.
prefsPtr is optional : when NULL is provided, preferences will be set to cover worst case scenario.
tech details :
@return if automatic flushing is not enabled, includes the possibility that internal buffer might already be filled by up to (blockSize-1) bytes.
It also includes frame footer (ending + checksum), since it might be generated by LZ4F_compressEnd().
@return doesn't include frame header, as it was already generated by LZ4F_compressBegin().
</p></pre><BR>
<pre><b>size_t LZ4F_compressUpdate(LZ4F_cctx* cctx,
void* dstBuffer, size_t dstCapacity,
const void* srcBuffer, size_t srcSize,
const LZ4F_compressOptions_t* cOptPtr);
</b><p> LZ4F_compressUpdate() can be called repetitively to compress as much data as necessary.
Important rule: dstCapacity MUST be large enough to ensure operation success even in worst case situations.
This value is provided by LZ4F_compressBound().
If this condition is not respected, LZ4F_compress() will fail (result is an errorCode).
After an error, the state is left in a UB state, and must be re-initialized or freed.
If previously an uncompressed block was written, buffered data is flushed
before appending compressed data is continued.
`cOptPtr` is optional : NULL can be provided, in which case all options are set to default.
@return : number of bytes written into `dstBuffer` (it can be zero, meaning input data was just buffered).
or an error code if it fails (which can be tested using LZ4F_isError())
</p></pre><BR>
<pre><b>size_t LZ4F_flush(LZ4F_cctx* cctx,
void* dstBuffer, size_t dstCapacity,
const LZ4F_compressOptions_t* cOptPtr);
</b><p> When data must be generated and sent immediately, without waiting for a block to be completely filled,
it's possible to call LZ4_flush(). It will immediately compress any data buffered within cctx.
`dstCapacity` must be large enough to ensure the operation will be successful.
`cOptPtr` is optional : it's possible to provide NULL, all options will be set to default.
@return : nb of bytes written into dstBuffer (can be zero, when there is no data stored within cctx)
or an error code if it fails (which can be tested using LZ4F_isError())
Note : LZ4F_flush() is guaranteed to be successful when dstCapacity >= LZ4F_compressBound(0, prefsPtr).
</p></pre><BR>
<pre><b>size_t LZ4F_compressEnd(LZ4F_cctx* cctx,
void* dstBuffer, size_t dstCapacity,
const LZ4F_compressOptions_t* cOptPtr);
</b><p> To properly finish an LZ4 frame, invoke LZ4F_compressEnd().
It will flush whatever data remained within `cctx` (like LZ4_flush())
and properly finalize the frame, with an endMark and a checksum.
`cOptPtr` is optional : NULL can be provided, in which case all options will be set to default.
@return : nb of bytes written into dstBuffer, necessarily >= 4 (endMark),
or an error code if it fails (which can be tested using LZ4F_isError())
Note : LZ4F_compressEnd() is guaranteed to be successful when dstCapacity >= LZ4F_compressBound(0, prefsPtr).
A successful call to LZ4F_compressEnd() makes `cctx` available again for another compression task.
</p></pre><BR>
<a name="Chapter9"></a><h2>Decompression functions</h2><pre></pre>
<pre><b>typedef struct {
unsigned stableDst; /* pledges that last 64KB decompressed data is present right before @dstBuffer pointer.
* This optimization skips internal storage operations.
* Once set, this pledge must remain valid up to the end of current frame. */
unsigned skipChecksums; /* disable checksum calculation and verification, even when one is present in frame, to save CPU time.
* Setting this option to 1 once disables all checksums for the rest of the frame. */
unsigned reserved1; </b>/* must be set to zero for forward compatibility */<b>
unsigned reserved0; </b>/* idem */<b>
} LZ4F_decompressOptions_t;
</b></pre><BR>
<pre><b>LZ4F_errorCode_t LZ4F_createDecompressionContext(LZ4F_dctx** dctxPtr, unsigned version);
LZ4F_errorCode_t LZ4F_freeDecompressionContext(LZ4F_dctx* dctx);
</b><p> Create an LZ4F_dctx object, to track all decompression operations.
@version provided MUST be LZ4F_VERSION.
@dctxPtr MUST be valid.
The function fills @dctxPtr with the value of a pointer to an allocated and initialized LZ4F_dctx object.
The @return is an errorCode, which can be tested using LZ4F_isError().
dctx memory can be released using LZ4F_freeDecompressionContext();
Result of LZ4F_freeDecompressionContext() indicates current state of decompressionContext when being released.
That is, it should be == 0 if decompression has been completed fully and correctly.
</p></pre><BR>
<a name="Chapter10"></a><h2>Streaming decompression functions</h2><pre></pre>
<pre><b>size_t LZ4F_headerSize(const void* src, size_t srcSize);
</b><p> Provide the header size of a frame starting at `src`.
`srcSize` must be >= LZ4F_MIN_SIZE_TO_KNOW_HEADER_LENGTH,
which is enough to decode the header length.
@return : size of frame header
or an error code, which can be tested using LZ4F_isError()
note : Frame header size is variable, but is guaranteed to be
>= LZ4F_HEADER_SIZE_MIN bytes, and <= LZ4F_HEADER_SIZE_MAX bytes.
</p></pre><BR>
<pre><b>size_t
LZ4F_getFrameInfo(LZ4F_dctx* dctx,
LZ4F_frameInfo_t* frameInfoPtr,
const void* srcBuffer, size_t* srcSizePtr);
</b><p> This function extracts frame parameters (max blockSize, dictID, etc.).
Its usage is optional: user can also invoke LZ4F_decompress() directly.
Extracted information will fill an existing LZ4F_frameInfo_t structure.
This can be useful for allocation and dictionary identification purposes.
LZ4F_getFrameInfo() can work in the following situations :
1) At the beginning of a new frame, before any invocation of LZ4F_decompress().
It will decode header from `srcBuffer`,
consuming the header and starting the decoding process.
Input size must be large enough to contain the full frame header.
Frame header size can be known beforehand by LZ4F_headerSize().
Frame header size is variable, but is guaranteed to be >= LZ4F_HEADER_SIZE_MIN bytes,
and not more than <= LZ4F_HEADER_SIZE_MAX bytes.
Hence, blindly providing LZ4F_HEADER_SIZE_MAX bytes or more will always work.
It's allowed to provide more input data than the header size,
LZ4F_getFrameInfo() will only consume the header.
If input size is not large enough,
aka if it's smaller than header size,
function will fail and return an error code.
2) After decoding has been started,
it's possible to invoke LZ4F_getFrameInfo() anytime
to extract already decoded frame parameters stored within dctx.
Note that, if decoding has barely started,
and not yet read enough information to decode the header,
LZ4F_getFrameInfo() will fail.
The number of bytes consumed from srcBuffer will be updated in *srcSizePtr (necessarily <= original value).
LZ4F_getFrameInfo() only consumes bytes when decoding has not yet started,
and when decoding the header has been successful.
Decompression must then resume from (srcBuffer + *srcSizePtr).
@return : a hint about how many srcSize bytes LZ4F_decompress() expects for next call,
or an error code which can be tested using LZ4F_isError().
note 1 : in case of error, dctx is not modified. Decoding operation can resume from beginning safely.
note 2 : frame parameters are *copied into* an already allocated LZ4F_frameInfo_t structure.
</p></pre><BR>
<pre><b>size_t
LZ4F_decompress(LZ4F_dctx* dctx,
void* dstBuffer, size_t* dstSizePtr,
const void* srcBuffer, size_t* srcSizePtr,
const LZ4F_decompressOptions_t* dOptPtr);
</b><p> Call this function repetitively to regenerate data compressed in `srcBuffer`.
The function requires a valid dctx state.
It will read up to *srcSizePtr bytes from srcBuffer,
and decompress data into dstBuffer, of capacity *dstSizePtr.
The nb of bytes consumed from srcBuffer will be written into *srcSizePtr (necessarily <= original value).
The nb of bytes decompressed into dstBuffer will be written into *dstSizePtr (necessarily <= original value).
The function does not necessarily read all input bytes, so always check value in *srcSizePtr.
Unconsumed source data must be presented again in subsequent invocations.
`dstBuffer` can freely change between each consecutive function invocation.
`dstBuffer` content will be overwritten.
Note: if `LZ4F_getFrameInfo()` is called before `LZ4F_decompress()`, srcBuffer must be updated to reflect
the number of bytes consumed after reading the frame header. Failure to update srcBuffer before calling
`LZ4F_decompress()` will cause decompression failure or, even worse, successful but incorrect decompression.
See the `LZ4F_getFrameInfo()` docs for details.
@return : an hint of how many `srcSize` bytes LZ4F_decompress() expects for next call.
Schematically, it's the size of the current (or remaining) compressed block + header of next block.
Respecting the hint provides some small speed benefit, because it skips intermediate buffers.
This is just a hint though, it's always possible to provide any srcSize.
When a frame is fully decoded, @return will be 0 (no more data expected).
When provided with more bytes than necessary to decode a frame,
LZ4F_decompress() will stop reading exactly at end of current frame, and @return 0.
If decompression failed, @return is an error code, which can be tested using LZ4F_isError().
After a decompression error, the `dctx` context is not resumable.
Use LZ4F_resetDecompressionContext() to return to clean state.
After a frame is fully decoded, dctx can be used again to decompress another frame.
</p></pre><BR>
<pre><b>void LZ4F_resetDecompressionContext(LZ4F_dctx* dctx); </b>/* always successful */<b>
</b><p> In case of an error, the context is left in "undefined" state.
In which case, it's necessary to reset it, before re-using it.
This method can also be used to abruptly stop any unfinished decompression,
and start a new one using same context resources.
</p></pre><BR>
<a name="Chapter11"></a><h2>Dictionary compression API</h2><pre></pre>
<pre><b>size_t
LZ4F_compressBegin_usingDict(LZ4F_cctx* cctx,
void* dstBuffer, size_t dstCapacity,
const void* dictBuffer, size_t dictSize,
const LZ4F_preferences_t* prefsPtr);
</b><p> Inits dictionary compression streaming, and writes the frame header into dstBuffer.
@dstCapacity must be >= LZ4F_HEADER_SIZE_MAX bytes.
@prefsPtr is optional : one may provide NULL as argument,
however, it's the only way to provide dictID in the frame header.
@dictBuffer must outlive the compression session.
@return : number of bytes written into dstBuffer for the header,
or an error code (which can be tested using LZ4F_isError())
NOTE: The LZ4Frame spec allows each independent block to be compressed with the dictionary,
but this entry supports a more limited scenario, where only the first block uses the dictionary.
This is still useful for small data, which only need one block anyway.
For larger inputs, one may be more interested in LZ4F_compressFrame_usingCDict() below.
</p></pre><BR>
<pre><b>size_t
LZ4F_decompress_usingDict(LZ4F_dctx* dctxPtr,
void* dstBuffer, size_t* dstSizePtr,
const void* srcBuffer, size_t* srcSizePtr,
const void* dict, size_t dictSize,
const LZ4F_decompressOptions_t* decompressOptionsPtr);
</b><p> Same as LZ4F_decompress(), using a predefined dictionary.
Dictionary is used "in place", without any preprocessing.
It must remain accessible throughout the entire frame decoding.
</p></pre><BR>
<a name="Chapter12"></a><h2>Bulk processing dictionary compression</h2><pre></pre>
<pre><b>LZ4F_CDict* LZ4F_createCDict(const void* dictBuffer, size_t dictSize);
void LZ4F_freeCDict(LZ4F_CDict* CDict);
</b><p> When compressing multiple messages / blocks using the same dictionary, it's recommended to initialize it just once.
LZ4_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
LZ4_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
@dictBuffer can be released after LZ4_CDict creation, since its content is copied within CDict.
</p></pre><BR>
<pre><b>size_t
LZ4F_compressFrame_usingCDict(LZ4F_cctx* cctx,
void* dst, size_t dstCapacity,
const void* src, size_t srcSize,
const LZ4F_CDict* cdict,
const LZ4F_preferences_t* preferencesPtr);
</b><p> Compress an entire srcBuffer into a valid LZ4 frame using a digested Dictionary.
@cctx must point to a context created by LZ4F_createCompressionContext().
If @cdict==NULL, compress without a dictionary.
@dstBuffer MUST be >= LZ4F_compressFrameBound(srcSize, preferencesPtr).
If this condition is not respected, function will fail (@return an errorCode).
The LZ4F_preferences_t structure is optional : one may provide NULL as argument,
but it's not recommended, as it's the only way to provide @dictID in the frame header.
@return : number of bytes written into dstBuffer.
or an error code if it fails (can be tested using LZ4F_isError())
Note: for larger inputs generating multiple independent blocks,
this entry point uses the dictionary for each block.
</p></pre><BR>
<pre><b>size_t
LZ4F_compressBegin_usingCDict(LZ4F_cctx* cctx,
void* dstBuffer, size_t dstCapacity,
const LZ4F_CDict* cdict,
const LZ4F_preferences_t* prefsPtr);
</b><p> Inits streaming dictionary compression, and writes the frame header into dstBuffer.
@dstCapacity must be >= LZ4F_HEADER_SIZE_MAX bytes.
@prefsPtr is optional : one may provide NULL as argument,
note however that it's the only way to insert a @dictID in the frame header.
@cdict must outlive the compression session.
@return : number of bytes written into dstBuffer for the header,
or an error code, which can be tested using LZ4F_isError().
</p></pre><BR>
<pre><b>typedef enum { LZ4F_LIST_ERRORS(LZ4F_GENERATE_ENUM)
_LZ4F_dummy_error_enum_for_c89_never_used } LZ4F_errorCodes;
</b></pre><BR>
<a name="Chapter13"></a><h2>Advanced compression operations</h2><pre></pre>
<pre><b>LZ4FLIB_STATIC_API size_t LZ4F_getBlockSize(LZ4F_blockSizeID_t blockSizeID);
</b><p> @return, in scalar format (size_t),
the maximum block size associated with @blockSizeID,
or an error code (can be tested using LZ4F_isError()) if @blockSizeID is invalid.
</p></pre><BR>
<pre><b>LZ4FLIB_STATIC_API size_t
LZ4F_uncompressedUpdate(LZ4F_cctx* cctx,
void* dstBuffer, size_t dstCapacity,
const void* srcBuffer, size_t srcSize,
const LZ4F_compressOptions_t* cOptPtr);
</b><p> LZ4F_uncompressedUpdate() can be called repetitively to add data stored as uncompressed blocks.
Important rule: dstCapacity MUST be large enough to store the entire source buffer as
no compression is done for this operation
If this condition is not respected, LZ4F_uncompressedUpdate() will fail (result is an errorCode).
After an error, the state is left in a UB state, and must be re-initialized or freed.
If previously a compressed block was written, buffered data is flushed first,
before appending uncompressed data is continued.
This operation is only supported when LZ4F_blockIndependent is used.
`cOptPtr` is optional : NULL can be provided, in which case all options are set to default.
@return : number of bytes written into `dstBuffer` (it can be zero, meaning input data was just buffered).
or an error code if it fails (which can be tested using LZ4F_isError())
</p></pre><BR>
<a name="Chapter14"></a><h2>Custom memory allocation</h2><pre></pre>
<pre><b>typedef void* (*LZ4F_AllocFunction) (void* opaqueState, size_t size);
typedef void* (*LZ4F_CallocFunction) (void* opaqueState, size_t size);
typedef void (*LZ4F_FreeFunction) (void* opaqueState, void* address);
typedef struct {
LZ4F_AllocFunction customAlloc;
LZ4F_CallocFunction customCalloc; </b>/* optional; when not defined, uses customAlloc + memset */<b>
LZ4F_FreeFunction customFree;
void* opaqueState;
} LZ4F_CustomMem;
static
#ifdef __GNUC__
__attribute__((__unused__))
#endif
LZ4F_CustomMem const LZ4F_defaultCMem = { NULL, NULL, NULL, NULL }; </b>/**< this constant defers to stdlib's functions */<b>
</b><p> These prototypes make it possible to pass custom allocation/free functions.
LZ4F_customMem is provided at state creation time, using LZ4F_create*_advanced() listed below.
All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones.
</p></pre><BR>
<pre><b>LZ4FLIB_STATIC_API size_t LZ4F_cctx_size(const LZ4F_cctx* cctx);
LZ4FLIB_STATIC_API size_t LZ4F_dctx_size(const LZ4F_dctx* dctx);
</b><p> These functions return the total memory footprint of the provided context.
</p></pre><BR>
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