/* 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 "../common/constants.h"

#include "../common/platform.h"

#if defined(__cplusplus) || defined(c_plusplus)

extern "C" {

#endif

#define BROTLI_REVERSE_BITS_MAX 8

#if defined(BROTLI_RBIT)

#define BROTLI_REVERSE_BITS_BASE \

  ((sizeof(brotli_reg_t) << 3) - BROTLI_REVERSE_BITS_MAX)

#else

#define BROTLI_REVERSE_BITS_BASE 0

static BROTLI_MODEL("small")

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 \

  ((brotli_reg_t)1 << (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 brotli_reg_t BrotliReverseBits(brotli_reg_t num) {

#if defined(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 */

  brotli_reg_t key;       /* prefix code */

  brotli_reg_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);

  BROTLI_DCHECK(BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH == 5);

  /* Generate offsets into sorted symbol table by code length. */

  symbol = -1;

  bits = 1;

  /* BROTLI_HUFFMAN_MAX_CODE_LENGTH_CODE_LENGTH == 5 */

  BROTLI_REPEAT_5({

    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 = ConstructHuffmanCode(0, (uint16_t)sorted[0]);

    for (key = 0; key < (brotli_reg_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 {

    for (bits_count = count[bits]; bits_count != 0; --bits_count) {

      code = ConstructHuffmanCode((uint8_t)bits, (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 */

  brotli_reg_t key;       /* prefix code */

  brotli_reg_t key_step;  /* prefix code addend */

  brotli_reg_t sub_key;   /* 2nd level table prefix code */

  brotli_reg_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 the root table. Reduce the table size to if possible,

     and create the repetitions by memcpy. */

  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 {

    symbol = bits - (BROTLI_HUFFMAN_MAX_CODE_LENGTH + 1);

    for (bits_count = count[bits]; bits_count != 0; --bits_count) {

      symbol = symbol_lists[symbol];

      code = ConstructHuffmanCode((uint8_t)bits, (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 then replicate to fill the remaining slots. */

  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] = ConstructHuffmanCode(

            (uint8_t)(table_bits + root_bits),

            (uint16_t)(((size_t)(table - root_table)) - sub_key));

        sub_key = 0;

      }

      symbol = symbol_lists[symbol];

      code = ConstructHuffmanCode((uint8_t)(len - root_bits), (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] = ConstructHuffmanCode(0, val[0]);

      break;

    case 1:

      if (val[1] > val[0]) {

        table[0] = ConstructHuffmanCode(1, val[0]);

        table[1] = ConstructHuffmanCode(1, val[1]);

      } else {

        table[0] = ConstructHuffmanCode(1, val[1]);

        table[1] = ConstructHuffmanCode(1, val[0]);

      }

      table_size = 2;

      break;

    case 2:

      table[0] = ConstructHuffmanCode(1, val[0]);

      table[2] = ConstructHuffmanCode(1, val[0]);

      if (val[2] > val[1]) {

        table[1] = ConstructHuffmanCode(2, val[1]);

        table[3] = ConstructHuffmanCode(2, val[2]);

      } else {

        table[1] = ConstructHuffmanCode(2, val[2]);

        table[3] = ConstructHuffmanCode(2, val[1]);

      }

      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;

          }

        }

      }

      table[0] = ConstructHuffmanCode(2, val[0]);

      table[2] = ConstructHuffmanCode(2, val[1]);

      table[1] = ConstructHuffmanCode(2, val[2]);

      table[3] = ConstructHuffmanCode(2, val[3]);

      table_size = 4;

      break;

    }

    case 4: {

      if (val[3] < val[2]) {

        uint16_t t = val[3];

        val[3] = val[2];

        val[2] = t;

      }

      table[0] = ConstructHuffmanCode(1, val[0]);

      table[1] = ConstructHuffmanCode(2, val[1]);

      table[2] = ConstructHuffmanCode(1, val[0]);

      table[3] = ConstructHuffmanCode(3, val[2]);

      table[4] = ConstructHuffmanCode(1, val[0]);

      table[5] = ConstructHuffmanCode(2, val[1]);

      table[6] = ConstructHuffmanCode(1, val[0]);

      table[7] = ConstructHuffmanCode(3, val[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