BaseTools/Source/C/BrotliCompress/enc/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 /* Functions to map previous bytes into a context id. */
   8
   9 #ifndef BROTLI_ENC_CONTEXT_H_
  10 #define BROTLI_ENC_CONTEXT_H_
  11
  12 #include "../common/types.h"
  13 #include "../common/port.h"
  14
  15 #if defined(__cplusplus) || defined(c_plusplus)
  16 extern "C" {
  17 #endif
  18
  19 /* Second-order context lookup table for UTF8 byte streams.
  20
  21    If p1 and p2 are the previous two bytes, we calculate the context as
  22
  23      context = kUTF8ContextLookup[p1] | kUTF8ContextLookup[p2 + 256].
  24
  25    If the previous two bytes are ASCII characters (i.e. < 128), this will be
  26    equivalent to
  27
  28      context = 4 * context1(p1) + context2(p2),
  29
  30    where context1 is based on the previous byte in the following way:
  31
  32      0  : non-ASCII control
  33      1  : \t, \n, \r
  34      2  : space
  35      3  : other punctuation
  36      4  : " '
  37      5  : %
  38      6  : ( < [ {
  39      7  : ) > ] }
  40      8  : , ; :
  41      9  : .
  42      10 : =
  43      11 : number
  44      12 : upper-case vowel
  45      13 : upper-case consonant
  46      14 : lower-case vowel
  47      15 : lower-case consonant
  48
  49    and context2 is based on the second last byte:
  50
  51      0 : control, space
  52      1 : punctuation
  53      2 : upper-case letter, number
  54      3 : lower-case letter
  55
  56    If the last byte is ASCII, and the second last byte is not (in a valid UTF8
  57    stream it will be a continuation byte, value between 128 and 191), the
  58    context is the same as if the second last byte was an ASCII control or space.
  59
  60    If the last byte is a UTF8 lead byte (value >= 192), then the next byte will
  61    be a continuation byte and the context id is 2 or 3 depending on the LSB of
  62    the last byte and to a lesser extent on the second last byte if it is ASCII.
  63
  64    If the last byte is a UTF8 continuation byte, the second last byte can be:
  65      - continuation byte: the next byte is probably ASCII or lead byte (assuming
  66        4-byte UTF8 characters are rare) and the context id is 0 or 1.
  67      - lead byte (192 - 207): next byte is ASCII or lead byte, context is 0 or 1
  68      - lead byte (208 - 255): next byte is continuation byte, context is 2 or 3
  69
  70    The possible value combinations of the previous two bytes, the range of
  71    context ids and the type of the next byte is summarized in the table below:
  72
  73    |--------\-----------------------------------------------------------------|
  74    |         \                         Last byte                              |
  75    | Second   \---------------------------------------------------------------|
  76    | last byte \    ASCII            |   cont. byte        |   lead byte      |
  77    |            \   (0-127)          |   (128-191)         |   (192-)         |
  78    |=============|===================|=====================|==================|
  79    |  ASCII      | next: ASCII/lead  |  not valid          |  next: cont.     |
  80    |  (0-127)    | context: 4 - 63   |                     |  context: 2 - 3  |
  81    |-------------|-------------------|---------------------|------------------|
  82    |  cont. byte | next: ASCII/lead  |  next: ASCII/lead   |  next: cont.     |
  83    |  (128-191)  | context: 4 - 63   |  context: 0 - 1     |  context: 2 - 3  |
  84    |-------------|-------------------|---------------------|------------------|
  85    |  lead byte  | not valid         |  next: ASCII/lead   |  not valid       |
  86    |  (192-207)  |                   |  context: 0 - 1     |                  |
  87    |-------------|-------------------|---------------------|------------------|
  88    |  lead byte  | not valid         |  next: cont.        |  not valid       |
  89    |  (208-)     |                   |  context: 2 - 3     |                  |
  90    |-------------|-------------------|---------------------|------------------|
  91 */
  92 static const uint8_t kUTF8ContextLookup[512] = {
  93   /* Last byte. */
  94   /* */
  95   /* ASCII range. */
  96    0,  0,  0,  0,  0,  0,  0,  0,  0,  4,  4,  0,  0,  4,  0,  0,
  97    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
  98    8, 12, 16, 12, 12, 20, 12, 16, 24, 28, 12, 12, 32, 12, 36, 12,
  99   44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 32, 32, 24, 40, 28, 12,
 100   12, 48, 52, 52, 52, 48, 52, 52, 52, 48, 52, 52, 52, 52, 52, 48,
 101   52, 52, 52, 52, 52, 48, 52, 52, 52, 52, 52, 24, 12, 28, 12, 12,
 102   12, 56, 60, 60, 60, 56, 60, 60, 60, 56, 60, 60, 60, 60, 60, 56,
 103   60, 60, 60, 60, 60, 56, 60, 60, 60, 60, 60, 24, 12, 28, 12,  0,
 104   /* UTF8 continuation byte range. */
 105   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 106   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 107   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 108   0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
 109   /* UTF8 lead byte range. */
 110   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 111   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 112   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 113   2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3,
 114   /* Second last byte. */
 115   /* */
 116   /* ASCII range. */
 117   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 118   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 119   0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 120   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1,
 121   1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 122   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1,
 123   1, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 124   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 1, 1, 1, 1, 0,
 125   /* UTF8 continuation byte range. */
 126   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 127   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 128   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 129   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 130   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 131   /* UTF8 lead byte range. */
 132   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 133   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 134   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 135 };
 136
 137 /* Context lookup table for small signed integers. */
 138 static const uint8_t kSigned3BitContextLookup[] = {
 139   0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 140   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 141   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 142   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 143   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 144   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 145   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 146   3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
 147   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 148   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 149   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 150   4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
 151   5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
 152   5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
 153   5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
 154   6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7,
 155 };
 156
 157 typedef enum ContextType {
 158   CONTEXT_LSB6         = 0,
 159   CONTEXT_MSB6         = 1,
 160   CONTEXT_UTF8         = 2,
 161   CONTEXT_SIGNED       = 3
 162 } ContextType;
 163
 164 static BROTLI_INLINE uint8_t Context(uint8_t p1, uint8_t p2, ContextType mode) {
 165   switch (mode) {
 166     case CONTEXT_LSB6:
 167       return p1 & 0x3f;
 168     case CONTEXT_MSB6:
 169       return (uint8_t)(p1 >> 2);
 170     case CONTEXT_UTF8:
 171       return kUTF8ContextLookup[p1] | kUTF8ContextLookup[p2 + 256];
 172     case CONTEXT_SIGNED:
 173       return (uint8_t)((kSigned3BitContextLookup[p1] << 3) +
 174                        kSigned3BitContextLookup[p2]);
 175     default:
 176       return 0;
 177   }
 178 }
 179
 180 #if defined(__cplusplus) || defined(c_plusplus)
 181 }  /* extern "C" */
 182 #endif
 183
 184 #endif  /* BROTLI_ENC_CONTEXT_H_ */