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      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 /* Utilities for building Huffman decoding tables. */
      8 
      9 #ifndef BROTLI_DEC_HUFFMAN_H_
     10 #define BROTLI_DEC_HUFFMAN_H_
     11 
     12 #include "../common/platform.h"
     13 #include <brotli/types.h>
     14 
     15 #if defined(__cplusplus) || defined(c_plusplus)
     16 extern "C" {
     17 #endif
     18 
     19 #define BROTLI_HUFFMAN_MAX_CODE_LENGTH 15
     20 
     21 /* BROTLI_NUM_BLOCK_LEN_SYMBOLS == 26 */
     22 #define BROTLI_HUFFMAN_MAX_SIZE_26 396
     23 /* BROTLI_MAX_BLOCK_TYPE_SYMBOLS == 258 */
     24 #define BROTLI_HUFFMAN_MAX_SIZE_258 632
     25 /* BROTLI_MAX_CONTEXT_MAP_SYMBOLS == 272 */
     26 #define BROTLI_HUFFMAN_MAX_SIZE_272 646
     27 
     28 #define BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH 5
     29 
     30 #if ((defined(BROTLI_TARGET_ARMV7) || defined(BROTLI_TARGET_ARMV8_32)) && \
     31   BROTLI_GNUC_HAS_ATTRIBUTE(aligned, 2, 7, 0))
     32 #define BROTLI_HUFFMAN_CODE_FAST_LOAD
     33 #endif
     34 
     35 #if !defined(BROTLI_HUFFMAN_CODE_FAST_LOAD)
     36 /* Do not create this struct directly - use the ConstructHuffmanCode
     37  * constructor below! */
     38 typedef struct {
     39   uint8_t bits;    /* number of bits used for this symbol */
     40   uint16_t value;  /* symbol value or table offset */
     41 } HuffmanCode;
     42 
     43 static BROTLI_INLINE HuffmanCode ConstructHuffmanCode(const uint8_t bits,
     44     const uint16_t value) {
     45   HuffmanCode h;
     46   h.bits = bits;
     47   h.value = value;
     48   return h;
     49 }
     50 
     51 /* Please use the following macros to optimize HuffmanCode accesses in hot
     52  * paths.
     53  *
     54  * For example, assuming |table| contains a HuffmanCode pointer:
     55  *
     56  *   BROTLI_HC_MARK_TABLE_FOR_FAST_LOAD(table);
     57  *   BROTLI_HC_ADJUST_TABLE_INDEX(table, index_into_table);
     58  *   *bits = BROTLI_HC_GET_BITS(table);
     59  *   *value = BROTLI_HC_GET_VALUE(table);
     60  *   BROTLI_HC_ADJUST_TABLE_INDEX(table, offset);
     61  *   *bits2 = BROTLI_HC_GET_BITS(table);
     62  *   *value2 = BROTLI_HC_GET_VALUE(table);
     63  *
     64  */
     65 
     66 #define BROTLI_HC_MARK_TABLE_FOR_FAST_LOAD(H)
     67 #define BROTLI_HC_ADJUST_TABLE_INDEX(H, V) H += (V)
     68 
     69 /* These must be given a HuffmanCode pointer! */
     70 #define BROTLI_HC_FAST_LOAD_BITS(H) (H->bits)
     71 #define BROTLI_HC_FAST_LOAD_VALUE(H) (H->value)
     72 
     73 #else /* BROTLI_HUFFMAN_CODE_FAST_LOAD */
     74 
     75 typedef BROTLI_ALIGNED(4) uint32_t HuffmanCode;
     76 
     77 static BROTLI_INLINE HuffmanCode ConstructHuffmanCode(const uint8_t bits,
     78     const uint16_t value) {
     79   return (HuffmanCode) ((value & 0xFFFF) << 16) | (bits & 0xFF);
     80 }
     81 
     82 #define BROTLI_HC_MARK_TABLE_FOR_FAST_LOAD(H) uint32_t __fastload_##H = (*H)
     83 #define BROTLI_HC_ADJUST_TABLE_INDEX(H, V) H += (V); __fastload_##H = (*H)
     84 
     85 /* These must be given a HuffmanCode pointer! */
     86 #define BROTLI_HC_FAST_LOAD_BITS(H) ((__fastload_##H) & 0xFF)
     87 #define BROTLI_HC_FAST_LOAD_VALUE(H) ((__fastload_##H) >> 16)
     88 #endif /* BROTLI_HUFFMAN_CODE_FAST_LOAD */
     89 
     90 /* Builds Huffman lookup table assuming code lengths are in symbol order. */
     91 BROTLI_INTERNAL void BrotliBuildCodeLengthsHuffmanTable(HuffmanCode* root_table,
     92     const uint8_t* const code_lengths, uint16_t* count);
     93 
     94 /* Builds Huffman lookup table assuming code lengths are in symbol order.
     95    Returns size of resulting table. */
     96 BROTLI_INTERNAL uint32_t BrotliBuildHuffmanTable(HuffmanCode* root_table,
     97     int root_bits, const uint16_t* const symbol_lists, uint16_t* count);
     98 
     99 /* Builds a simple Huffman table. The |num_symbols| parameter is to be
    100    interpreted as follows: 0 means 1 symbol, 1 means 2 symbols,
    101    2 means 3 symbols, 3 means 4 symbols with lengths [2, 2, 2, 2],
    102    4 means 4 symbols with lengths [1, 2, 3, 3]. */
    103 BROTLI_INTERNAL uint32_t BrotliBuildSimpleHuffmanTable(HuffmanCode* table,
    104     int root_bits, uint16_t* symbols, uint32_t num_symbols);
    105 
    106 /* Contains a collection of Huffman trees with the same alphabet size. */
    107 /* alphabet_size_limit is needed due to simple codes, since
    108    log2(alphabet_size_max) could be greater than log2(alphabet_size_limit). */
    109 typedef struct {
    110   HuffmanCode** htrees;
    111   HuffmanCode* codes;
    112   uint16_t alphabet_size_max;
    113   uint16_t alphabet_size_limit;
    114   uint16_t num_htrees;
    115 } HuffmanTreeGroup;
    116 
    117 #if defined(__cplusplus) || defined(c_plusplus)
    118 }  /* extern "C" */
    119 #endif
    120 
    121 #endif  /* BROTLI_DEC_HUFFMAN_H_ */
    122