// Copyright 2012 Google Inc. All Rights Reserved.

//

// Use of this source code is governed by a BSD-style license

// that can be found in the COPYING file in the root of the source

// tree. An additional intellectual property rights grant can be found

// in the file PATENTS. All contributing project authors may

// be found in the AUTHORS file in the root of the source tree.

// -----------------------------------------------------------------------------

//

// Utilities for building and looking up Huffman trees.

//

// Author: Urvang Joshi (urvang@google.com)

#include <assert.h>

#include <stdlib.h>

#include <string.h>

#include "src/utils/huffman_utils.h"

#include "src/utils/utils.h"

#include "src/webp/format_constants.h"

// Huffman data read via DecodeImageStream is represented in two (red and green)

// bytes.

#define MAX_HTREE_GROUPS    0x10000

HTreeGroup* VP8LHtreeGroupsNew(int num_htree_groups) {

  HTreeGroup* const htree_groups =

      (HTreeGroup*)WebPSafeMalloc(num_htree_groups, sizeof(*htree_groups));

  if (htree_groups == NULL) {

    return NULL;

  }

  assert(num_htree_groups <= MAX_HTREE_GROUPS);

  return htree_groups;

}

void VP8LHtreeGroupsFree(HTreeGroup* const htree_groups) {

  if (htree_groups != NULL) {

    WebPSafeFree(htree_groups);

  }

}

// Returns reverse(reverse(key, len) + 1, len), where reverse(key, len) is the

// bit-wise reversal of the len least significant bits of key.

static WEBP_INLINE uint32_t GetNextKey(uint32_t key, int len) {

  uint32_t step = 1 << (len - 1);

  while (key & step) {

    step >>= 1;

  }

  return step ? (key & (step - 1)) + step : key;

}

// Stores code in table[0], table[step], table[2*step], ..., table[end].

// Assumes that end is an integer multiple of step.

static WEBP_INLINE void ReplicateValue(HuffmanCode* table,

                                       int step, int end,

                                       HuffmanCode code) {

  assert(end % step == 0);

  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 WEBP_INLINE int NextTableBitSize(const int* const count,

                                        int len, int root_bits) {

  int left = 1 << (len - root_bits);

  while (len < MAX_ALLOWED_CODE_LENGTH) {

    left -= count[len];

    if (left <= 0) break;

    ++len;

    left <<= 1;

  }

  return len - root_bits;

}

// sorted[code_lengths_size] is a pre-allocated array for sorting symbols

// by code length.

static int BuildHuffmanTable(HuffmanCode* const root_table, int root_bits,

                             const int code_lengths[], int code_lengths_size,

                             uint16_t sorted[]) {

  HuffmanCode* table = root_table;  // next available space in table

  int total_size = 1 << root_bits;  // total size root table + 2nd level table

  int len;                          // current code length

  int symbol;                       // symbol index in original or sorted table

  // number of codes of each length:

  int count[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 };

  // offsets in sorted table for each length:

  int offset[MAX_ALLOWED_CODE_LENGTH + 1];

  assert(code_lengths_size != 0);

  assert(code_lengths != NULL);

  assert(root_table != NULL);

  assert(root_bits > 0);

  // Build histogram of code lengths.

  for (symbol = 0; symbol < code_lengths_size; ++symbol) {

    if (code_lengths[symbol] > MAX_ALLOWED_CODE_LENGTH) {

      return 0;

    }

    ++count[code_lengths[symbol]];

  }

  // Error, all code lengths are zeros.

  if (count[0] == code_lengths_size) {

    return 0;

  }

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

  offset[1] = 0;

  for (len = 1; len < MAX_ALLOWED_CODE_LENGTH; ++len) {

    if (count[len] > (1 << len)) {

      return 0;

    }

    offset[len + 1] = offset[len] + count[len];

  }

  // Sort symbols by length, by symbol order within each length.

  for (symbol = 0; symbol < code_lengths_size; ++symbol) {

    const int symbol_code_length = code_lengths[symbol];

    if (code_lengths[symbol] > 0) {

      sorted[offset[symbol_code_length]++] = symbol;

    }

  }

  // Special case code with only one value.

  if (offset[MAX_ALLOWED_CODE_LENGTH] == 1) {

    HuffmanCode code;

    code.bits = 0;

    code.value = (uint16_t)sorted[0];

    ReplicateValue(table, 1, total_size, code);

    return total_size;

  }

  {

    int step;              // step size to replicate values in current table

    uint32_t low = -1;     // low bits for current root entry

    uint32_t mask = total_size - 1;    // mask for low bits

    uint32_t key = 0;      // reversed prefix code

    int num_nodes = 1;     // number of Huffman tree nodes

    int num_open = 1;      // number of open branches in current tree level

    int table_bits = root_bits;        // key length of current table

    int table_size = 1 << table_bits;  // size of current table

    symbol = 0;

    // Fill in root table.

    for (len = 1, step = 2; len <= root_bits; ++len, step <<= 1) {

      num_open <<= 1;

      num_nodes += num_open;

      num_open -= count[len];

      if (num_open < 0) {

        return 0;

      }

      for (; count[len] > 0; --count[len]) {

        HuffmanCode code;

        code.bits = (uint8_t)len;

        code.value = (uint16_t)sorted[symbol++];

        ReplicateValue(&table[key], step, table_size, code);

        key = GetNextKey(key, len);

      }

    }

    // Fill in 2nd level tables and add pointers to root table.

    for (len = root_bits + 1, step = 2; len <= MAX_ALLOWED_CODE_LENGTH;

         ++len, step <<= 1) {

      num_open <<= 1;

      num_nodes += num_open;

      num_open -= count[len];

      if (num_open < 0) {

        return 0;

      }

      for (; count[len] > 0; --count[len]) {

        HuffmanCode code;

        if ((key & mask) != low) {

          table += table_size;

          table_bits = NextTableBitSize(count, len, root_bits);

          table_size = 1 << table_bits;

          total_size += table_size;

          low = key & mask;

          root_table[low].bits = (uint8_t)(table_bits + root_bits);

          root_table[low].value = (uint16_t)((table - root_table) - low);

        }

        code.bits = (uint8_t)(len - root_bits);

        code.value = (uint16_t)sorted[symbol++];

        ReplicateValue(&table[key >> root_bits], step, table_size, code);

        key = GetNextKey(key, len);

      }

    }

    // Check if tree is full.

    if (num_nodes != 2 * offset[MAX_ALLOWED_CODE_LENGTH] - 1) {

      return 0;

    }

  }

  return total_size;

}

// Maximum code_lengths_size is 2328 (reached for 11-bit color_cache_bits).

// More commonly, the value is around ~280.

#define MAX_CODE_LENGTHS_SIZE \

  ((1 << MAX_CACHE_BITS) + NUM_LITERAL_CODES + NUM_LENGTH_CODES)

// Cut-off value for switching between heap and stack allocation.

#define SORTED_SIZE_CUTOFF 512

int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,

                          const int code_lengths[], int code_lengths_size) {

  int total_size;

  assert(code_lengths_size <= MAX_CODE_LENGTHS_SIZE);

  if (code_lengths_size <= SORTED_SIZE_CUTOFF) {

    // use local stack-allocated array.

    uint16_t sorted[SORTED_SIZE_CUTOFF];

    total_size = BuildHuffmanTable(root_table, root_bits,

                                   code_lengths, code_lengths_size, sorted);

  } else {   // rare case. Use heap allocation.

    uint16_t* const sorted =

        (uint16_t*)WebPSafeMalloc(code_lengths_size, sizeof(*sorted));

    if (sorted == NULL) return 0;

    total_size = BuildHuffmanTable(root_table, root_bits,

                                   code_lengths, code_lengths_size, sorted);

    WebPSafeFree(sorted);

  }

  return total_size;

}