1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>1.8.2 Manual</title>
</head>
<body>
<h1>1.8.2 Manual</h1>
<hr>
<a name="Contents"></a><h2>Contents</h2>
<ol>
<li><a href="#Chapter1">Introduction</a></li>
<li><a href="#Chapter2">Version</a></li>
<li><a href="#Chapter3">Tuning parameter</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">Unstable declarations</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 at 400 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.
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 provides block compression functions. It gives full buffer control to user.
Decompressing an lz4-compressed block also requires metadata (such as compressed size).
Each application is free to encode such metadata in whichever way it wants.
An additional format, called LZ4 frame specification (doc/lz4_Frame_format.md),
take care of encoding standard metadata alongside LZ4-compressed blocks.
If your application requires interoperability, it's recommended to use it.
A library is provided to take care of it, see lz4frame.h.
<BR></pre>
<a name="Chapter2"></a><h2>Version</h2><pre></pre>
<pre><b>int LZ4_versionNumber (void); </b>/**< library version number; useful to check dll version */<b>
</b></pre><BR>
<pre><b>const char* LZ4_versionString (void); </b>/**< library version string; unseful to check dll version */<b>
</b></pre><BR>
<a name="Chapter3"></a><h2>Tuning parameter</h2><pre></pre>
<pre><b>#ifndef LZ4_MEMORY_USAGE
# define LZ4_MEMORY_USAGE 14
#endif
</b><p> Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
Increasing memory usage improves compression ratio
Reduced memory usage may improve speed, thanks to cache effect
Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache
</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.
Note : as a consequence, 'dst' content is not valid.
Note 2 : This function is protected against buffer overflow scenarios (never writes outside 'dst' buffer, nor read outside 'source' buffer).
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
</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.
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.
This function is protected against malicious data packets.
</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 ACCELERATION_DEFAULT (currently == 1, 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 compression function, just using an externally allocated memory space to store compression state.
Use LZ4_sizeofState() to know how much memory must be allocated,
and allocate it on 8-bytes boundaries (using malloc() typically).
Then, provide it 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 'targetDestSize'.
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'.
*srcSizePtr : will be modified to indicate how many bytes where read from 'src' to fill 'dst'.
New value is necessarily <= old value.
return : Nb bytes written into 'dst' (necessarily <= targetDestSize)
or 0 if compression fails
</p></pre><BR>
<pre><b>int LZ4_decompress_fast (const char* src, char* dst, int originalSize);
</b><p>This function is a bit faster than LZ4_decompress_safe(),
but it may misbehave on malformed input because it doesn't perform full validation of compressed data.
originalSize : is the uncompressed size to regenerate
Destination buffer must be already allocated, and its size must be >= 'originalSize' bytes.
return : number of bytes read from source buffer (== compressed size).
If the source stream is detected malformed, the function stops decoding and return a negative result.
note : This function is only usable if the originalSize of uncompressed data is known in advance.
The caller should also check that all the compressed input has been consumed properly,
i.e. that the return value matches the size of the buffer with compressed input.
The function never writes past the output buffer. However, since it doesn't know its 'src' size,
it may read past the intended input. Also, because match offsets are not validated during decoding,
reads from 'src' may underflow. Use this function in trusted environment **only**.
</p></pre><BR>
<pre><b>int LZ4_decompress_safe_partial (const char* src, char* dst, int srcSize, int targetOutputSize, int dstCapacity);
</b><p> This function decompress a compressed block of size 'srcSize' at position 'src'
into destination buffer 'dst' of size 'dstCapacity'.
The function will decompress a minimum of 'targetOutputSize' bytes, and stop after that.
However, it's not accurate, and may write more than 'targetOutputSize' (but always <= dstCapacity).
@return : the number of bytes decoded in the destination buffer (necessarily <= dstCapacity)
Note : this number can also be < targetOutputSize, if compressed block contains less data.
Therefore, always control how many bytes were decoded.
If source stream is detected malformed, function returns a negative result.
This function is protected against malicious data packets.
</p></pre><BR>
<a name="Chapter6"></a><h2>Streaming Compression Functions</h2><pre></pre>
<pre><b>LZ4_stream_t* LZ4_createStream(void);
int LZ4_freeStream (LZ4_stream_t* streamPtr);
</b><p> LZ4_createStream() will allocate and initialize an `LZ4_stream_t` structure.
LZ4_freeStream() releases its memory.
</p></pre><BR>
<pre><b>void LZ4_resetStream (LZ4_stream_t* streamPtr);
</b><p> An LZ4_stream_t structure can be allocated once and re-used multiple times.
Use this function to start compressing a new stream.
</p></pre><BR>
<pre><b>int LZ4_loadDict (LZ4_stream_t* streamPtr, const char* dictionary, int dictSize);
</b><p> Use this function to load a static dictionary into LZ4_stream_t.
Any previous data will be forgotten, only 'dictionary' will remain in memory.
Loading a size of 0 is allowed, and is the same as reset.
@return : dictionary size, in bytes (necessarily <= 64 KB)
</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.
Important : The previous 64KB of compressed data is assumed to remain present and unmodified in memory!
Special 1 : When input is a double-buffer, they can have any size, including < 64 KB.
Make sure that buffers are separated by at least one byte.
This way, each block only depends on previous block.
Special 2 : If input buffer is a ring-buffer, it can have any size, including < 64 KB.
@return : size of compressed block
or 0 if there is an error (typically, cannot fit into 'dst').
After an error, the stream status is 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>LZ4_streamDecode_t* LZ4_createStreamDecode(void);
int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream);
</b><p> creation / destruction of streaming decompression tracking structure.
A tracking structure can be re-used multiple times sequentially.
</p></pre><BR>
<pre><b>int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dictionary, int dictSize);
</b><p> An LZ4_streamDecode_t structure can be allocated once and re-used multiple times.
Use this function to start decompression of a new stream of blocks.
A dictionary can optionnally be set. Use NULL or size 0 for a reset order.
@return : 1 if OK, 0 if error
</p></pre><BR>
<pre><b>int LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int srcSize, int dstCapacity);
int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int originalSize);
</b><p> These decoding functions allow decompression of consecutive blocks in "streaming" mode.
A block is an unsplittable entity, it must be presented entirely to a decompression function.
Decompression functions only accept one block at a time.
The last 64KB of previously decoded data *must* remain available and unmodified at the memory position where they were decoded.
If less than 64KB of data has been decoded all the data must be present.
Special : if application sets a ring buffer for decompression, it must respect one of the following conditions :
- Exactly same size as encoding buffer, with same update rule (block boundaries at same positions)
In which case, the decoding & encoding ring buffer can have any size, including very small ones ( < 64 KB).
- Larger than encoding buffer, by a minimum of maxBlockSize more bytes.
maxBlockSize is implementation dependent. It's the maximum size of any single block.
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).
- _At least_ 64 KB + 8 bytes + maxBlockSize.
In which case, encoding and decoding buffers do not need to be synchronized,
and encoding ring buffer can have any size, including larger than decoding buffer.
Whenever these conditions are not possible, save the last 64KB of decoded data into a safe buffer,
and indicate where it 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 dstCapcity, const char* dictStart, int dictSize);
int LZ4_decompress_fast_usingDict (const char* src, char* dst, int originalSize, const char* dictStart, int dictSize);
</b><p> These decoding functions work the same as
a combination of LZ4_setStreamDecode() followed by LZ4_decompress_*_continue()
They are stand-alone, and don't need an LZ4_streamDecode_t structure.
</p></pre><BR>
<a name="Chapter8"></a><h2>Unstable declarations</h2><pre>
Declarations in this section should be considered unstable.
Use at your own peril, etc., etc.
They may be removed in the future.
Their signatures may change.
<BR></pre>
<pre><b>void LZ4_resetStream_fast (LZ4_stream_t* streamPtr);
</b><p> When an LZ4_stream_t is known to be in a internally coherent state,
it can often be prepared for a new compression with almost no work, only
sometimes falling back to the full, expensive reset that is always required
when the stream is in an indeterminate state (i.e., the reset performed by
LZ4_resetStream()).
LZ4_streams are guaranteed to be in a valid state when:
- returned from LZ4_createStream()
- reset by LZ4_resetStream()
- memset(stream, 0, sizeof(LZ4_stream_t))
- the stream was in a valid state and was reset by LZ4_resetStream_fast()
- the stream was in a valid state and was then used in any compression call
that returned success
- the stream was in an indeterminate state and was used in a compression
call that fully reset the state (LZ4_compress_fast_extState()) and that
returned success
</p></pre><BR>
<pre><b>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 LZ4_resetStream_fast() while
LZ4_compress_fast_extState() starts with a call to LZ4_resetStream().
</p></pre><BR>
<pre><b>void LZ4_attach_dictionary(LZ4_stream_t *working_stream, const LZ4_stream_t *dictionary_stream);
</b><p> This is an experimental API that allows for the efficient use of a
static dictionary many 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 the dictionary stream in-place.
Several assumptions are made about the state of the dictionary stream.
Currently, only streams which have been prepared by LZ4_loadDict() should
be expected to work.
Alternatively, the provided dictionary stream pointer 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. The dictionary
stream (and source buffer) must remain in-place / accessible / unchanged
through the completion of the first compression call on the stream.
</p></pre><BR>
<a name="Chapter9"></a><h2>Private definitions</h2><pre>
Do not use these definitions.
They are exposed to allow static allocation of `LZ4_stream_t` and `LZ4_streamDecode_t`.
Using these definitions will expose code to API and/or ABI break in future versions of the library.
<BR></pre>
<pre><b>typedef struct {
const uint8_t* externalDict;
size_t extDictSize;
const uint8_t* prefixEnd;
size_t prefixSize;
} LZ4_streamDecode_t_internal;
</b></pre><BR>
<pre><b>typedef struct {
const unsigned char* externalDict;
size_t extDictSize;
const unsigned char* prefixEnd;
size_t prefixSize;
} LZ4_streamDecode_t_internal;
</b></pre><BR>
<pre><b>#define LZ4_STREAMSIZE_U64 ((1 << (LZ4_MEMORY_USAGE-3)) + 4)
#define LZ4_STREAMSIZE (LZ4_STREAMSIZE_U64 * sizeof(unsigned long long))
union LZ4_stream_u {
unsigned long long table[LZ4_STREAMSIZE_U64];
LZ4_stream_t_internal internal_donotuse;
} ; </b>/* previously typedef'd to LZ4_stream_t */<b>
</b><p> information structure to track an LZ4 stream.
init this structure before first use.
note : only use in association with static linking !
this definition is not API/ABI safe,
it may change in a future version !
</p></pre><BR>
<pre><b>#define LZ4_STREAMDECODESIZE_U64 4
#define LZ4_STREAMDECODESIZE (LZ4_STREAMDECODESIZE_U64 * sizeof(unsigned long long))
union LZ4_streamDecode_u {
unsigned long long table[LZ4_STREAMDECODESIZE_U64];
LZ4_streamDecode_t_internal internal_donotuse;
} ; </b>/* previously typedef'd to LZ4_streamDecode_t */<b>
</b><p> information structure to track an LZ4 stream during decompression.
init this structure using LZ4_setStreamDecode (or memset()) before first use
note : only use in association with static linking !
this definition is not API/ABI safe,
and may change in a future version !
</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
# define LZ4_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
# if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b>
# define LZ4_DEPRECATED(message) [[deprecated(message)]]
# elif (LZ4_GCC_VERSION >= 405) || defined(__clang__)
# define LZ4_DEPRECATED(message) __attribute__((deprecated(message)))
# elif (LZ4_GCC_VERSION >= 301)
# define LZ4_DEPRECATED(message) __attribute__((deprecated))
# elif defined(_MSC_VER)
# define LZ4_DEPRECATED(message) __declspec(deprecated(message))
# else
# pragma message("WARNING: You need to implement LZ4_DEPRECATED for this compiler")
# define LZ4_DEPRECATED(message)
# endif
#endif </b>/* LZ4_DISABLE_DEPRECATE_WARNINGS */<b>
</b><p> 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.
Otherwise, it's also possible to define LZ4_DISABLE_DEPRECATE_WARNINGS
</p></pre><BR>
</html>
</body>
|
