brotli/dec/huffman.c

/* 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. */

#include "./huffman.h"

#include <string.h>  /* memcpy, memset */

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

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

#define BROTLI_REVERSE_BITS_MAX 8

#ifdef BROTLI_RBIT
#define BROTLI_REVERSE_BITS_BASE (32 - BROTLI_REVERSE_BITS_MAX)
#else
#define BROTLI_REVERSE_BITS_BASE 0
static uint8_t kReverseBits[1 << BROTLI_REVERSE_BITS_MAX] = {
  0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0,
  0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
  0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
  0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
  0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4,
  0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
  0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC,
  0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
  0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
  0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
  0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,
  0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
  0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6,
  0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
  0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
  0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
  0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1,
  0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
  0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9,
  0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
  0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
  0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
  0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED,
  0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
  0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3,
  0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
  0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
  0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
  0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7,
  0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
  0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF,
  0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
};
#endif  /* BROTLI_RBIT */

#define BROTLI_REVERSE_BITS_LOWEST \
  (1U << (BROTLI_REVERSE_BITS_MAX - 1 + BROTLI_REVERSE_BITS_BASE))

/* Returns reverse(num >> BROTLI_REVERSE_BITS_BASE, BROTLI_REVERSE_BITS_MAX),
   where reverse(value, len) is the bit-wise reversal of the len least
   significant bits of value. */
static BROTLI_INLINE uint32_t BrotliReverseBits(uint32_t num) {
#ifdef BROTLI_RBIT
  return BROTLI_RBIT(num);
#else
  return kReverseBits[num];
#endif
}

/* Stores code in table[0], table[step], table[2*step], ..., table[end] */
/* Assumes that end is an integer multiple of step */
static BROTLI_INLINE void ReplicateValue(HuffmanCode* table,
                                         int step, int end,
                                         HuffmanCode code) {
  do {
    end -= step;
    table[end] = code;
  } while (end > 0);
}

/* Returns the table width of the next 2nd level table. count is the histogram
   of bit lengths for the remaining symbols, len is the code length of the next
   processed symbol */
static BROTLI_INLINE int NextTableBitSize(const uint16_t* const count,
                                          int len, int root_bits) {
  int left = 1 << (len - root_bits);
  while (len < BROTLI_HUFFMAN_MAX_CODE_LENGTH) {
    left -= count[len];
    if (left <= 0) break;
    ++len;
    left <<= 1;
  }
  return len - root_bits;
}

void BrotliBuildCodeLengthsHuffmanTable(HuffmanCode* table,
                                        const uint8_t* const code_lengths,
                                        uint16_t* count) {
  HuffmanCode code;   /* current table entry */
  int symbol;         /* symbol index in original or sorted table */
  uint32_t key;       /* prefix code */
  uint32_t key_step;  /* prefix code addend */
  int step;           /* step size to replicate values in current table */
  int table_size;     /* size of current table */
  int sorted[BROTLI_CODE_LENGTH_CODES];  /* symbols sorted by code length */
  /* offsets in sorted table for each length */
  int offset[BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH + 1];
  int bits;
  int bits_count;
  BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH <=
                BROTLI_REVERSE_BITS_MAX);

  /* generate offsets into sorted symbol table by code length */
  symbol = -1;
  bits = 1;
  BROTLI_REPEAT(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH, {
    symbol += count[bits];
    offset[bits] = symbol;
    bits++;
  });
  /* Symbols with code length 0 are placed after all other symbols. */
  offset[0] = BROTLI_CODE_LENGTH_CODES - 1;

  /* sort symbols by length, by symbol order within each length */
  symbol = BROTLI_CODE_LENGTH_CODES;
  do {
    BROTLI_REPEAT(6, {
      symbol--;
      sorted[offset[code_lengths[symbol]]--] = symbol;
    });
  } while (symbol != 0);

  table_size = 1 << BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH;

  /* Special case: all symbols but one have 0 code length. */
  if (offset[0] == 0) {
    code.bits = 0;
    code.value = (uint16_t)sorted[0];
    for (key = 0; key < (uint32_t)table_size; ++key) {
      table[key] = code;
    }
    return;
  }

  /* fill in table */
  key = 0;
  key_step = BROTLI_REVERSE_BITS_LOWEST;
  symbol = 0;
  bits = 1;
  step = 2;
  do {
    code.bits = (uint8_t)bits;
    for (bits_count = count[bits]; bits_count != 0; --bits_count) {
      code.value = (uint16_t)sorted[symbol++];
      ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code);
      key += key_step;
    }
    step <<= 1;
    key_step >>= 1;
  } while (++bits <= BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH);
}

uint32_t BrotliBuildHuffmanTable(HuffmanCode* root_table,
                                 int root_bits,
                                 const uint16_t* const symbol_lists,
                                 uint16_t* count) {
  HuffmanCode code;       /* current table entry */
  HuffmanCode* table;     /* next available space in table */
  int len;                /* current code length */
  int symbol;             /* symbol index in original or sorted table */
  uint32_t key;           /* prefix code */
  uint32_t key_step;      /* prefix code addend */
  uint32_t sub_key;       /* 2nd level table prefix code */
  uint32_t sub_key_step;  /* 2nd level table prefix code addend */
  int step;               /* step size to replicate values in current table */
  int table_bits;         /* key length of current table */
  int table_size;         /* size of current table */
  int total_size;         /* sum of root table size and 2nd level table sizes */
  int max_length = -1;
  int bits;
  int bits_count;

  BROTLI_DCHECK(root_bits <= BROTLI_REVERSE_BITS_MAX);
  BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH - root_bits <=
                BROTLI_REVERSE_BITS_MAX);

  while (symbol_lists[max_length] == 0xFFFF) max_length--;
  max_length += BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1;

  table = root_table;
  table_bits = root_bits;
  table_size = 1 << table_bits;
  total_size = table_size;

  /* fill in root table */
  /* let's reduce the table size to a smaller size if possible, and */
  /* create the repetitions by memcpy if possible in the coming loop */
  if (table_bits > max_length) {
    table_bits = max_length;
    table_size = 1 << table_bits;
  }
  key = 0;
  key_step = BROTLI_REVERSE_BITS_LOWEST;
  bits = 1;
  step = 2;
  do {
    code.bits = (uint8_t)bits;
    symbol = bits - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1);
    for (bits_count = count[bits]; bits_count != 0; --bits_count) {
      symbol = symbol_lists[symbol];
      code.value = (uint16_t)symbol;
      ReplicateValue(&table[BrotliReverseBits(key)], step, table_size, code);
      key += key_step;
    }
    step <<= 1;
    key_step >>= 1;
  } while (++bits <= table_bits);

  /* if root_bits != table_bits we only created one fraction of the */
  /* table, and we need to replicate it now. */
  while (total_size != table_size) {
    memcpy(&table[table_size], &table[0],
           (size_t)table_size * sizeof(table[0]));
    table_size <<= 1;
  }

  /* fill in 2nd level tables and add pointers to root table */
  key_step = BROTLI_REVERSE_BITS_LOWEST >> (root_bits - 1);
  sub_key = (BROTLI_REVERSE_BITS_LOWEST << 1);
  sub_key_step = BROTLI_REVERSE_BITS_LOWEST;
  for (len = root_bits + 1, step = 2; len <= max_length; ++len) {
    symbol = len - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1);
    for (; count[len] != 0; --count[len]) {
      if (sub_key == (BROTLI_REVERSE_BITS_LOWEST << 1U)) {
        table += table_size;
        table_bits = NextTableBitSize(count, len, root_bits);
        table_size = 1 << table_bits;
        total_size += table_size;
        sub_key = BrotliReverseBits(key);
        key += key_step;
        root_table[sub_key].bits = (uint8_t)(table_bits + root_bits);
        root_table[sub_key].value =
            (uint16_t)(((size_t)(table - root_table)) - sub_key);
        sub_key = 0;
      }
      code.bits = (uint8_t)(len - root_bits);
      symbol = symbol_lists[symbol];
      code.value = (uint16_t)symbol;
      ReplicateValue(
          &table[BrotliReverseBits(sub_key)], step, table_size, code);
      sub_key += sub_key_step;
    }
    step <<= 1;
    sub_key_step >>= 1;
  }
  return (uint32_t)total_size;
}

uint32_t BrotliBuildSimpleHuffmanTable(HuffmanCode* table,
                                       int root_bits,
                                       uint16_t* val,
                                       uint32_t num_symbols) {
  uint32_t table_size = 1;
  const uint32_t goal_size = 1U << root_bits;
  switch (num_symbols) {
    case 0:
      table[0].bits = 0;
      table[0].value = val[0];
      break;
    case 1:
      table[0].bits = 1;
      table[1].bits = 1;
      if (val[1] > val[0]) {
        table[0].value = val[0];
        table[1].value = val[1];
      } else {
        table[0].value = val[1];
        table[1].value = val[0];
      }
      table_size = 2;
      break;
    case 2:
      table[0].bits = 1;
      table[0].value = val[0];
      table[2].bits = 1;
      table[2].value = val[0];
      if (val[2] > val[1]) {
        table[1].value = val[1];
        table[3].value = val[2];
      } else {
        table[1].value = val[2];
        table[3].value = val[1];
      }
      table[1].bits = 2;
      table[3].bits = 2;
      table_size = 4;
      break;
    case 3: {
      int i, k;
      for (i = 0; i < 3; ++i) {
        for (k = i + 1; k < 4; ++k) {
          if (val[k] < val[i]) {
            uint16_t t = val[k];
            val[k] = val[i];
            val[i] = t;
          }
        }
      }
      for (i = 0; i < 4; ++i) {
        table[i].bits = 2;
      }
      table[0].value = val[0];
      table[2].value = val[1];
      table[1].value = val[2];
      table[3].value = val[3];
      table_size = 4;
      break;
    }
    case 4: {
      int i;
      if (val[3] < val[2]) {
        uint16_t t = val[3];
        val[3] = val[2];
        val[2] = t;
      }
      for (i = 0; i < 7; ++i) {
        table[i].value = val[0];
        table[i].bits = (uint8_t)(1 + (i & 1));
      }
      table[1].value = val[1];
      table[3].value = val[2];
      table[5].value = val[1];
      table[7].value = val[3];
      table[3].bits = 3;
      table[7].bits = 3;
      table_size = 8;
      break;
    }
  }
  while (table_size != goal_size) {
    memcpy(&table[table_size], &table[0],
           (size_t)table_size * sizeof(table[0]));
    table_size <<= 1;
  }
  return goal_size;
}

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