MdeModulePkg/Library/BrotliCustomDecompressLib/dec/context.h

   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 /* Lookup table to map the previous two bytes to a context id.
   8
   9    There are four different context modeling modes defined here:
  10      CONTEXT_LSB6: context id is the least significant 6 bits of the last byte,
  11      CONTEXT_MSB6: context id is the most significant 6 bits of the last byte,
  12      CONTEXT_UTF8: second-order context model tuned for UTF8-encoded text,
  13      CONTEXT_SIGNED: second-order context model tuned for signed integers.
  14
  15    The context id for the UTF8 context model is calculated as follows. If p1
  16    and p2 are the previous two bytes, we calculate the context as
  17
  18      context = kContextLookup[p1] | kContextLookup[p2 + 256].
  19
  20    If the previous two bytes are ASCII characters (i.e. < 128), this will be
  21    equivalent to
  22
  23      context = 4 * context1(p1) + context2(p2),
  24
  25    where context1 is based on the previous byte in the following way:
  26
  27      0  : non-ASCII control
  28      1  : \t, \n, \r
  29      2  : space
  30      3  : other punctuation
  31      4  : " '
  32      5  : %
  33      6  : ( < [ {
  34      7  : ) > ] }
  35      8  : , ; :
  36      9  : .
  37      10 : =
  38      11 : number
  39      12 : upper-case vowel
  40      13 : upper-case consonant
  41      14 : lower-case vowel
  42      15 : lower-case consonant
  43
  44    and context2 is based on the second last byte:
  45
  46      0 : control, space
  47      1 : punctuation
  48      2 : upper-case letter, number
  49      3 : lower-case letter
  50
  51    If the last byte is ASCII, and the second last byte is not (in a valid UTF8
  52    stream it will be a continuation byte, value between 128 and 191), the
  53    context is the same as if the second last byte was an ASCII control or space.
  54
  55    If the last byte is a UTF8 lead byte (value >= 192), then the next byte will
  56    be a continuation byte and the context id is 2 or 3 depending on the LSB of
  57    the last byte and to a lesser extent on the second last byte if it is ASCII.
  58
  59    If the last byte is a UTF8 continuation byte, the second last byte can be:
  60      - continuation byte: the next byte is probably ASCII or lead byte (assuming
  61        4-byte UTF8 characters are rare) and the context id is 0 or 1.
  62      - lead byte (192 - 207): next byte is ASCII or lead byte, context is 0 or 1
  63      - lead byte (208 - 255): next byte is continuation byte, context is 2 or 3
  64
  65    The possible value combinations of the previous two bytes, the range of
  66    context ids and the type of the next byte is summarized in the table below:
  67
  68    |--------\-----------------------------------------------------------------|
  69    |         \                         Last byte                              |
  70    | Second   \---------------------------------------------------------------|
  71    | last byte \    ASCII            |   cont. byte        |   lead byte      |
  72    |            \   (0-127)          |   (128-191)         |   (192-)         |
  73    |=============|===================|=====================|==================|
  74    |  ASCII      | next: ASCII/lead  |  not valid          |  next: cont.     |
  75    |  (0-127)    | context: 4 - 63   |                     |  context: 2 - 3  |
  76    |-------------|-------------------|---------------------|------------------|
  77    |  cont. byte | next: ASCII/lead  |  next: ASCII/lead   |  next: cont.     |
  78    |  (128-191)  | context: 4 - 63   |  context: 0 - 1     |  context: 2 - 3  |
  79    |-------------|-------------------|---------------------|------------------|
  80    |  lead byte  | not valid         |  next: ASCII/lead   |  not valid       |
  81    |  (192-207)  |                   |  context: 0 - 1     |                  |
  82    |-------------|-------------------|---------------------|------------------|
  83    |  lead byte  | not valid         |  next: cont.        |  not valid       |
  84    |  (208-)     |                   |  context: 2 - 3     |                  |
  85    |-------------|-------------------|---------------------|------------------|
  86
  87    The context id for the signed context mode is calculated as:
  88
  89      context = (kContextLookup[512 + p1] << 3) | kContextLookup[512 + p2].
  90
  91    For any context modeling modes, the context ids can be calculated by |-ing
  92    together two lookups from one table using context model dependent offsets:
  93
  94      context = kContextLookup[offset1 + p1] | kContextLookup[offset2 + p2].
  95
  96    where offset1 and offset2 are dependent on the context mode.
  97 */
  98
  99 #ifndef BROTLI_DEC_CONTEXT_H_
 100 #define BROTLI_DEC_CONTEXT_H_
 101
 102 #include "../common/types.h"
 103
 104 enum ContextType {
 105   CONTEXT_LSB6 = 0,
 106   CONTEXT_MSB6 = 1,
 107   CONTEXT_UTF8 = 2,
 108   CONTEXT_SIGNED = 3
 109 };
 110
 111 /* Common context lookup table for all context modes. */
 112 static const uint8_t kContextLookup[1792] = {
 113   /* CONTEXT_UTF8, last byte. */
 114   /* ASCII range. */
 115    0,  0,  0,  0,  0,  0,  0,  0,  0,  4,  4,  0,  0,  4,  0,  0,
 116    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
 117    8, 12, 16, 12, 12, 20, 12, 16, 24, 28, 12, 12, 32, 12, 36, 12,
 118   44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 32, 32, 24, 40, 28, 12,
 119   12, 48, 52, 52, 52, 48, 52, 52, 52, 48, 52, 52, 52, 52, 52, 48,
 120   52, 52, 52, 52, 52, 48, 52, 52, 52, 52, 52, 24, 12, 28, 12, 12,
 121   12, 56, 60, 60, 60, 56, 60, 60, 60, 56, 60, 60, 60, 60, 60, 56,
 122   60, 60, 60, 60, 60, 56, 60, 60, 60, 60, 60, 24, 12, 28, 12,  0,
 123   /* UTF8 continuation byte range. */
 124   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 125   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 126   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 127   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 128   /* UTF8 lead byte range. */
 129   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 130   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 131   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 132   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 133   /* CONTEXT_UTF8 second last byte. */
 134   /* ASCII range. */
 135   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 136   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 137   0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 138   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1,
 139   1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 140   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1,
 141   1, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 142   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 1, 1, 1, 1, 0,
 143   /* UTF8 continuation byte range. */
 144   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 145   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 146   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 147   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 148   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 149   /* UTF8 lead byte range. */
 150   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 151   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 152   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 153   /* CONTEXT_SIGNED, second last byte. */
 154   0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 155   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 156   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 157   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 158   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 159   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 160   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 161   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 162   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 163   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 164   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 165   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 166   5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
 167   5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
 168   5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
 169   6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7,
 170   /* CONTEXT_SIGNED, last byte, same as the above values shifted by 3 bits. */
 171    0, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
 172   16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
 173   16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
 174   16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16,
 175   24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
 176   24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
 177   24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
 178   24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
 179   32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32,
 180   32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32,
 181   32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32,
 182   32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32,
 183   40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
 184   40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
 185   40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40,
 186   48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 56,
 187   /* CONTEXT_LSB6, last byte. */
 188    0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
 189   16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
 190   32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
 191   48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
 192    0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
 193   16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
 194   32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
 195   48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
 196    0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
 197   16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
 198   32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
 199   48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
 200    0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
 201   16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
 202   32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
 203   48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
 204   /* CONTEXT_MSB6, last byte. */
 205    0,  0,  0,  0,  1,  1,  1,  1,  2,  2,  2,  2,  3,  3,  3,  3,
 206    4,  4,  4,  4,  5,  5,  5,  5,  6,  6,  6,  6,  7,  7,  7,  7,
 207    8,  8,  8,  8,  9,  9,  9,  9, 10, 10, 10, 10, 11, 11, 11, 11,
 208   12, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15,
 209   16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 19,
 210   20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 23, 23, 23, 23,
 211   24, 24, 24, 24, 25, 25, 25, 25, 26, 26, 26, 26, 27, 27, 27, 27,
 212   28, 28, 28, 28, 29, 29, 29, 29, 30, 30, 30, 30, 31, 31, 31, 31,
 213   32, 32, 32, 32, 33, 33, 33, 33, 34, 34, 34, 34, 35, 35, 35, 35,
 214   36, 36, 36, 36, 37, 37, 37, 37, 38, 38, 38, 38, 39, 39, 39, 39,
 215   40, 40, 40, 40, 41, 41, 41, 41, 42, 42, 42, 42, 43, 43, 43, 43,
 216   44, 44, 44, 44, 45, 45, 45, 45, 46, 46, 46, 46, 47, 47, 47, 47,
 217   48, 48, 48, 48, 49, 49, 49, 49, 50, 50, 50, 50, 51, 51, 51, 51,
 218   52, 52, 52, 52, 53, 53, 53, 53, 54, 54, 54, 54, 55, 55, 55, 55,
 219   56, 56, 56, 56, 57, 57, 57, 57, 58, 58, 58, 58, 59, 59, 59, 59,
 220   60, 60, 60, 60, 61, 61, 61, 61, 62, 62, 62, 62, 63, 63, 63, 63,
 221   /* CONTEXT_{M,L}SB6, second last byte, */
 222   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 223   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 224   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 225   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 226   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 227   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 228   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 229   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 230   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 231   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 232   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 233   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 234   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 235   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 236   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 237   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 238 };
 239
 240 static const int kContextLookupOffsets[8] = {
 241   /* CONTEXT_LSB6 */
 242   1024, 1536,
 243   /* CONTEXT_MSB6 */
 244   1280, 1536,
 245   /* CONTEXT_UTF8 */
 246   0, 256,
 247   /* CONTEXT_SIGNED */
 248   768, 512,
 249 };
 250
 251 #endif  /* BROTLI_DEC_CONTEXT_H_ */