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      1 /* Copyright 2016 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 #ifndef BROTLI_COMMON_CONSTANTS_H_
      8 #define BROTLI_COMMON_CONSTANTS_H_
      9 
     10 /* Specification: 7.3. Encoding of the context map */
     11 #define BROTLI_CONTEXT_MAP_MAX_RLE 16
     12 
     13 /* Specification: 2. Compressed representation overview */
     14 #define BROTLI_MAX_NUMBER_OF_BLOCK_TYPES 256
     15 
     16 /* Specification: 3.3. Alphabet sizes: insert-and-copy length */
     17 #define BROTLI_NUM_LITERAL_SYMBOLS 256
     18 #define BROTLI_NUM_COMMAND_SYMBOLS 704
     19 #define BROTLI_NUM_BLOCK_LEN_SYMBOLS 26
     20 #define BROTLI_MAX_CONTEXT_MAP_SYMBOLS (BROTLI_MAX_NUMBER_OF_BLOCK_TYPES + \
     21                                         BROTLI_CONTEXT_MAP_MAX_RLE)
     22 #define BROTLI_MAX_BLOCK_TYPE_SYMBOLS (BROTLI_MAX_NUMBER_OF_BLOCK_TYPES + 2)
     23 
     24 /* Specification: 3.5. Complex prefix codes */
     25 #define BROTLI_REPEAT_PREVIOUS_CODE_LENGTH 16
     26 #define BROTLI_REPEAT_ZERO_CODE_LENGTH 17
     27 #define BROTLI_CODE_LENGTH_CODES (BROTLI_REPEAT_ZERO_CODE_LENGTH + 1)
     28 /* "code length of 8 is repeated" */
     29 #define BROTLI_INITIAL_REPEATED_CODE_LENGTH 8
     30 
     31 /* Specification: 4. Encoding of distances */
     32 #define BROTLI_NUM_DISTANCE_SHORT_CODES 16
     33 #define BROTLI_MAX_NPOSTFIX 3
     34 #define BROTLI_MAX_NDIRECT 120
     35 #define BROTLI_MAX_DISTANCE_BITS 24U
     36 /* BROTLI_NUM_DISTANCE_SYMBOLS == 520 */
     37 #define BROTLI_NUM_DISTANCE_SYMBOLS (BROTLI_NUM_DISTANCE_SHORT_CODES + \
     38                                      BROTLI_MAX_NDIRECT +              \
     39                                      (BROTLI_MAX_DISTANCE_BITS <<      \
     40                                       (BROTLI_MAX_NPOSTFIX + 1)))
     41 /* Distance that is guaranteed to be representable in any stream. */
     42 #define BROTLI_MAX_DISTANCE 0x3FFFFFC
     43 
     44 /* 7.1. Context modes and context ID lookup for literals */
     45 /* "context IDs for literals are in the range of 0..63" */
     46 #define BROTLI_LITERAL_CONTEXT_BITS 6
     47 
     48 /* 7.2. Context ID for distances */
     49 #define BROTLI_DISTANCE_CONTEXT_BITS 2
     50 
     51 /* 9.1. Format of the Stream Header */
     52 /* Number of slack bytes for window size. Don't confuse
     53    with BROTLI_NUM_DISTANCE_SHORT_CODES. */
     54 #define BROTLI_WINDOW_GAP 16
     55 #define BROTLI_MAX_BACKWARD_LIMIT(W) (((size_t)1 << (W)) - BROTLI_WINDOW_GAP)
     56 
     57 #endif  /* BROTLI_COMMON_CONSTANTS_H_ */
     58