huffman.h

Go to the documentation of this file.

/* Copyright 2013 Google Inc. All Rights Reserved.

   Distributed under MIT license.
   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/

/* Utilities for building Huffman decoding tables. */

#ifndef BROTLI_DEC_HUFFMAN_H_
#define BROTLI_DEC_HUFFMAN_H_

#include "./types.h"
#include "./port.h"

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif

#define BROTLI_HUFFMAN_MAX_CODE_LENGTH 15

/* For current format this constant equals to kNumInsertAndCopyCodes */
#define BROTLI_HUFFMAN_MAX_CODE_LENGTHS_SIZE 704

/* Maximum possible Huffman table size for an alphabet size of (index * 32),
 * max code length 15 and root table bits 8. */
static const uint16_t kMaxHuffmanTableSize[] = {
  256, 402, 436, 468, 500, 534, 566, 598, 630, 662, 694, 726, 758, 790, 822,
  854, 886, 920, 952, 984, 1016, 1048, 1080};
#define BROTLI_HUFFMAN_MAX_SIZE_26 396
#define BROTLI_HUFFMAN_MAX_SIZE_258 632
#define BROTLI_HUFFMAN_MAX_SIZE_272 646

#define BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH 5

typedef struct {
  uint8_t bits;    /* number of bits used for this symbol */
  uint16_t value;  /* symbol value or table offset */
} HuffmanCode;

/* Builds Huffman lookup table assuming code lengths are in symbol order. */
BROTLI_INTERNAL void BrotliBuildCodeLengthsHuffmanTable(HuffmanCode* root_table,
    const uint8_t* const code_lengths, uint16_t* count);

/* Builds Huffman lookup table assuming code lengths are in symbol order. */
/* Returns size of resulting table. */
BROTLI_INTERNAL uint32_t BrotliBuildHuffmanTable(HuffmanCode* root_table,
    int root_bits, const uint16_t* const symbol_lists, uint16_t* count_arg);

/* Builds a simple Huffman table. The num_symbols parameter is to be */
/* interpreted as follows: 0 means 1 symbol, 1 means 2 symbols, 2 means 3 */
/* symbols, 3 means 4 symbols with lengths 2,2,2,2, 4 means 4 symbols with */
/* lengths 1,2,3,3. */
BROTLI_INTERNAL uint32_t BrotliBuildSimpleHuffmanTable(HuffmanCode* table,
    int root_bits, uint16_t* symbols, uint32_t num_symbols);

/* Contains a collection of Huffman trees with the same alphabet size. */
typedef struct {
  HuffmanCode** htrees;
  HuffmanCode* codes;
  uint16_t alphabet_size;
  uint16_t num_htrees;
} HuffmanTreeGroup;

#if defined(__cplusplus) || defined(c_plusplus)
}  /* extern "C" */
#endif

#endif  /* BROTLI_DEC_HUFFMAN_H_ */