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kc3-lang/brotli/enc/context.h
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Author :
Eugene Kliuchnikov
Date : 2016-09-21 17:20:36
Hash : 0a63f99d
Message : Update encoder * move `common/port.h` to `includes/port.h` * replace magic more magic numbers with constants * artificially limit window size to 2^18 for quality 0 and 1 * use fixed shifts for quality 0 and 1 hashes * removed `BrotliEncoderWriteMetadata` * added `BROTLI_OPERATION_EMIT_METADATA` instead * deprecated low-level API * fixed MSVC warnings
- enc/context.h
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/* Copyright 2013 Google Inc. All Rights Reserved. Distributed under MIT license. See file LICENSE for detail or copy at https://opensource.org/licenses/MIT */ /* Functions to map previous bytes into a context id. */ #ifndef BROTLI_ENC_CONTEXT_H_ #define BROTLI_ENC_CONTEXT_H_ #include <brotli/port.h> #include <brotli/types.h> #if defined(__cplusplus) || defined(c_plusplus) extern "C" { #endif /* Second-order context lookup table for UTF8 byte streams. If p1 and p2 are the previous two bytes, we calculate the context as context = kUTF8ContextLookup[p1] | kUTF8ContextLookup[p2 + 256]. If the previous two bytes are ASCII characters (i.e. < 128), this will be equivalent to context = 4 * context1(p1) + context2(p2), where context1 is based on the previous byte in the following way: 0 : non-ASCII control 1 : \t, \n, \r 2 : space 3 : other punctuation 4 : " ' 5 : % 6 : ( < [ { 7 : ) > ] } 8 : , ; : 9 : . 10 : = 11 : number 12 : upper-case vowel 13 : upper-case consonant 14 : lower-case vowel 15 : lower-case consonant and context2 is based on the second last byte: 0 : control, space 1 : punctuation 2 : upper-case letter, number 3 : lower-case letter If the last byte is ASCII, and the second last byte is not (in a valid UTF8 stream it will be a continuation byte, value between 128 and 191), the context is the same as if the second last byte was an ASCII control or space. If the last byte is a UTF8 lead byte (value >= 192), then the next byte will be a continuation byte and the context id is 2 or 3 depending on the LSB of the last byte and to a lesser extent on the second last byte if it is ASCII. If the last byte is a UTF8 continuation byte, the second last byte can be: - continuation byte: the next byte is probably ASCII or lead byte (assuming 4-byte UTF8 characters are rare) and the context id is 0 or 1. - lead byte (192 - 207): next byte is ASCII or lead byte, context is 0 or 1 - lead byte (208 - 255): next byte is continuation byte, context is 2 or 3 The possible value combinations of the previous two bytes, the range of context ids and the type of the next byte is summarized in the table below: |--------\-----------------------------------------------------------------| | \ Last byte | | Second \---------------------------------------------------------------| | last byte \ ASCII | cont. byte | lead byte | | \ (0-127) | (128-191) | (192-) | |=============|===================|=====================|==================| | ASCII | next: ASCII/lead | not valid | next: cont. | | (0-127) | context: 4 - 63 | | context: 2 - 3 | |-------------|-------------------|---------------------|------------------| | cont. byte | next: ASCII/lead | next: ASCII/lead | next: cont. | | (128-191) | context: 4 - 63 | context: 0 - 1 | context: 2 - 3 | |-------------|-------------------|---------------------|------------------| | lead byte | not valid | next: ASCII/lead | not valid | | (192-207) | | context: 0 - 1 | | |-------------|-------------------|---------------------|------------------| | lead byte | not valid | next: cont. | not valid | | (208-) | | context: 2 - 3 | | |-------------|-------------------|---------------------|------------------| */ static const uint8_t kUTF8ContextLookup[512] = { /* Last byte. */ /* */ /* ASCII range. */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 4, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 12, 16, 12, 12, 20, 12, 16, 24, 28, 12, 12, 32, 12, 36, 12, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 32, 32, 24, 40, 28, 12, 12, 48, 52, 52, 52, 48, 52, 52, 52, 48, 52, 52, 52, 52, 52, 48, 52, 52, 52, 52, 52, 48, 52, 52, 52, 52, 52, 24, 12, 28, 12, 12, 12, 56, 60, 60, 60, 56, 60, 60, 60, 56, 60, 60, 60, 60, 60, 56, 60, 60, 60, 60, 60, 56, 60, 60, 60, 60, 60, 24, 12, 28, 12, 0, /* UTF8 continuation byte range. */ 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, /* UTF8 lead byte range. */ 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, /* Second last byte. */ /* */ /* ASCII range. */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 1, 1, 1, 1, 0, /* UTF8 continuation byte range. */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* UTF8 lead byte range. */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, }; /* Context lookup table for small signed integers. */ static const uint8_t kSigned3BitContextLookup[] = { 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, }; typedef enum ContextType { CONTEXT_LSB6 = 0, CONTEXT_MSB6 = 1, CONTEXT_UTF8 = 2, CONTEXT_SIGNED = 3 } ContextType; static BROTLI_INLINE uint8_t Context(uint8_t p1, uint8_t p2, ContextType mode) { switch (mode) { case CONTEXT_LSB6: return p1 & 0x3f; case CONTEXT_MSB6: return (uint8_t)(p1 >> 2); case CONTEXT_UTF8: return kUTF8ContextLookup[p1] | kUTF8ContextLookup[p2 + 256]; case CONTEXT_SIGNED: return (uint8_t)((kSigned3BitContextLookup[p1] << 3) + kSigned3BitContextLookup[p2]); default: return 0; } } #if defined(__cplusplus) || defined(c_plusplus) } /* extern "C" */ #endif #endif /* BROTLI_ENC_CONTEXT_H_ */