github.com/andybalholm/brotli@v1.0.6/constants.go (about)

     1  package brotli
     2  
     3  /* Copyright 2016 Google Inc. All Rights Reserved.
     4  
     5     Distributed under MIT license.
     6     See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
     7  */
     8  
     9  /* Specification: 7.3. Encoding of the context map */
    10  const contextMapMaxRle = 16
    11  
    12  /* Specification: 2. Compressed representation overview */
    13  const maxNumberOfBlockTypes = 256
    14  
    15  /* Specification: 3.3. Alphabet sizes: insert-and-copy length */
    16  const numLiteralSymbols = 256
    17  
    18  const numCommandSymbols = 704
    19  
    20  const numBlockLenSymbols = 26
    21  
    22  const maxContextMapSymbols = (maxNumberOfBlockTypes + contextMapMaxRle)
    23  
    24  const maxBlockTypeSymbols = (maxNumberOfBlockTypes + 2)
    25  
    26  /* Specification: 3.5. Complex prefix codes */
    27  const repeatPreviousCodeLength = 16
    28  
    29  const repeatZeroCodeLength = 17
    30  
    31  const codeLengthCodes = (repeatZeroCodeLength + 1)
    32  
    33  /* "code length of 8 is repeated" */
    34  const initialRepeatedCodeLength = 8
    35  
    36  /* "Large Window Brotli" */
    37  const largeMaxDistanceBits = 62
    38  
    39  const largeMinWbits = 10
    40  
    41  const largeMaxWbits = 30
    42  
    43  /* Specification: 4. Encoding of distances */
    44  const numDistanceShortCodes = 16
    45  
    46  const maxNpostfix = 3
    47  
    48  const maxNdirect = 120
    49  
    50  const maxDistanceBits = 24
    51  
    52  func distanceAlphabetSize(NPOSTFIX uint, NDIRECT uint, MAXNBITS uint) uint {
    53  	return numDistanceShortCodes + NDIRECT + uint(MAXNBITS<<(NPOSTFIX+1))
    54  }
    55  
    56  /* numDistanceSymbols == 1128 */
    57  const numDistanceSymbols = 1128
    58  
    59  const maxDistance = 0x3FFFFFC
    60  
    61  const maxAllowedDistance = 0x7FFFFFFC
    62  
    63  /* 7.1. Context modes and context ID lookup for literals */
    64  /* "context IDs for literals are in the range of 0..63" */
    65  const literalContextBits = 6
    66  
    67  /* 7.2. Context ID for distances */
    68  const distanceContextBits = 2
    69  
    70  /* 9.1. Format of the Stream Header */
    71  /* Number of slack bytes for window size. Don't confuse
    72     with BROTLI_NUM_DISTANCE_SHORT_CODES. */
    73  const windowGap = 16
    74  
    75  func maxBackwardLimit(W uint) uint {
    76  	return (uint(1) << W) - windowGap
    77  }