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1 /* Copyright 2013 Google Inc. All Rights Reserved.
2 
3    Distributed under MIT license.
4    See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
5 */
6 
7 /* Collection of static dictionary words. */
8 
9 #ifndef BROTLI_COMMON_DICTIONARY_H_
10 #define BROTLI_COMMON_DICTIONARY_H_
11 
12 #include <brotli/port.h>
13 #include <brotli/types.h>
14 
15 #if defined(__cplusplus) || defined(c_plusplus)
16 extern "C" {
17 #endif
18 
19 typedef struct BrotliDictionary {
20   /**
21    * Number of bits to encode index of dictionary word in a bucket.
22    *
23    * Specification: Appendix A. Static Dictionary Data
24    *
25    * Words in a dictionary are bucketed by length.
26    * @c 0 means that there are no words of a given length.
27    * Dictionary consists of words with length of [4..24] bytes.
28    * Values at [0..3] and [25..31] indices should not be addressed.
29    */
30   uint8_t size_bits_by_length[32];
31 
32   /* assert(offset[i + 1] == offset[i] + (bits[i] ? (i << bits[i]) : 0)) */
33   uint32_t offsets_by_length[32];
34 
35   /* assert(data_size == offsets_by_length[31]) */
36   size_t data_size;
37 
38   /* Data array is not bound, and should obey to size_bits_by_length values.
39      Specified size matches default (RFC 7932) dictionary. Its size is
40      defined by data_size */
41   const uint8_t* data;
42 } BrotliDictionary;
43 
44 BROTLI_COMMON_API const BrotliDictionary* BrotliGetDictionary(void);
45 
46 /**
47  * Sets dictionary data.
48  *
49  * When dictionary data is already set / present, this method is no-op.
50  *
51  * Dictionary data MUST be provided before BrotliGetDictionary is invoked.
52  * This method is used ONLY in multi-client environment (e.g. C + Java),
53  * to reduce storage by sharing single dictionary between implementations.
54  */
55 BROTLI_COMMON_API void BrotliSetDictionaryData(const uint8_t* data);
56 
57 #define BROTLI_MIN_DICTIONARY_WORD_LENGTH 4
58 #define BROTLI_MAX_DICTIONARY_WORD_LENGTH 24
59 
60 #if defined(__cplusplus) || defined(c_plusplus)
61 }  /* extern "C" */
62 #endif
63 
64 #endif  /* BROTLI_COMMON_DICTIONARY_H_ */
65