BaseTools/Source/C/BrotliCompress/enc/prefix.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 for encoding of integers into prefix codes the amount of extra
   8    bits, and the actual values of the extra bits. */
   9
  10 #ifndef BROTLI_ENC_PREFIX_H_
  11 #define BROTLI_ENC_PREFIX_H_
  12
  13 #include "../common/constants.h"
  14 #include "../common/platform.h"
  15 #include <brotli/types.h>
  16 #include "./fast_log.h"
  17
  18 #if defined(__cplusplus) || defined(c_plusplus)
  19 extern "C" {
  20 #endif
  21
  22 /* Here distance_code is an intermediate code, i.e. one of the special codes or
  23    the actual distance increased by BROTLI_NUM_DISTANCE_SHORT_CODES - 1. */
  24 static BROTLI_INLINE void PrefixEncodeCopyDistance(size_t distance_code,
  25                                                    size_t num_direct_codes,
  26                                                    size_t postfix_bits,
  27                                                    uint16_t* code,
  28                                                    uint32_t* extra_bits) {
  29   if (distance_code < BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes) {
  30     *code = (uint16_t)distance_code;
  31     *extra_bits = 0;
  32     return;
  33   } else {
  34     size_t dist = ((size_t)1 << (postfix_bits + 2u)) +
  35         (distance_code - BROTLI_NUM_DISTANCE_SHORT_CODES - num_direct_codes);
  36     size_t bucket = Log2FloorNonZero(dist) - 1;
  37     size_t postfix_mask = (1u << postfix_bits) - 1;
  38     size_t postfix = dist & postfix_mask;
  39     size_t prefix = (dist >> bucket) & 1;
  40     size_t offset = (2 + prefix) << bucket;
  41     size_t nbits = bucket - postfix_bits;
  42     *code = (uint16_t)((nbits << 10) |
  43         (BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes +
  44          ((2 * (nbits - 1) + prefix) << postfix_bits) + postfix));
  45     *extra_bits = (uint32_t)((dist - offset) >> postfix_bits);
  46   }
  47 }
  48
  49 #if defined(__cplusplus) || defined(c_plusplus)
  50 }  /* extern "C" */
  51 #endif
  52
  53 #endif  /* BROTLI_ENC_PREFIX_H_ */