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273 lines
10 KiB
C#
273 lines
10 KiB
C#
//! \file Huffman.cs
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//! \date Wed May 18 22:19:23 2016
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//! \brief Google WEBP Huffman compression implementaion.
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/*
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Copyright (c) 2010, Google Inc. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are
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met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in
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the documentation and/or other materials provided with the
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distribution.
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* Neither the name of Google nor the names of its contributors may
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be used to endorse or promote products derived from this software
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without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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//
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// C# port by morkt (C) 2016
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//
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namespace GameRes.Formats.Google
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{
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static class Huffman
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{
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public const int CodesPerMetaCode = 5;
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public const int PackedBits = 6;
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public const int PackedTableSize = 1 << PackedBits;
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public const int DefaultCodeLength = 8;
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public const int MaxAllowedCodeLength = 15;
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public const int NumLiteralCodes = 256;
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public const int NumLengthCodes = 24;
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public const int NumDistanceCodes = 40;
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public const int CodeLengthCodes = 19;
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public const int MinBits = 2; // min number of Huffman bits
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public const int MaxBits = 9; // max number of Huffman bits
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public const int TableBits = 8;
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public const int TableMask = (1 << TableBits) - 1;
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public const int LengthsTableBits = 7;
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public const int LengthsTableMask = (1 << LengthsTableBits) - 1;
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static uint GetNextKey (uint key, int len)
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{
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uint step = 1u << (len - 1);
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while (0 != (key & step))
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step >>= 1;
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return (key & (step - 1)) + step;
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}
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public static int BuildTable (HuffmanCode[] root_table, int index, int root_bits, int[] code_lengths, int code_lengths_size)
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{
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int table = index; // next available space in table
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int total_size = 1 << root_bits; // total size root table + 2nd level table
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int len; // current code length
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int symbol; // symbol index in original or sorted table
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// number of codes of each length:
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int[] count = new int[MaxAllowedCodeLength + 1];
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// offsets in sorted table for each length:
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int[] offset = new int[MaxAllowedCodeLength + 1];
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// Build histogram of code lengths.
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for (symbol = 0; symbol < code_lengths_size; ++symbol)
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{
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if (code_lengths[symbol] > MaxAllowedCodeLength)
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return 0;
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++count[code_lengths[symbol]];
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}
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// Error, all code lengths are zeros.
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if (count[0] == code_lengths_size)
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return 0;
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// Generate offsets into sorted symbol table by code length.
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offset[1] = 0;
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for (len = 1; len < MaxAllowedCodeLength; ++len)
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{
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if (count[len] > (1 << len))
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return 0;
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offset[len + 1] = offset[len] + count[len];
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}
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var sorted = new int[code_lengths_size];
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// Sort symbols by length, by symbol order within each length.
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for (symbol = 0; symbol < code_lengths_size; ++symbol)
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{
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int symbol_code_length = code_lengths[symbol];
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if (code_lengths[symbol] > 0)
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sorted[offset[symbol_code_length]++] = symbol;
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}
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// Special case code with only one value.
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if (offset[MaxAllowedCodeLength] == 1)
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{
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HuffmanCode code;
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code.bits = 0;
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code.value = (ushort)sorted[0];
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ReplicateValue (root_table, table, 1, total_size, code);
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return total_size;
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}
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int step; // step size to replicate values in current table
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uint low = uint.MaxValue; // low bits for current root entry
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uint mask = (uint)total_size - 1; // mask for low bits
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uint key = 0; // reversed prefix code
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int num_nodes = 1; // number of Huffman tree nodes
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int num_open = 1; // number of open branches in current tree level
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int table_bits = root_bits; // key length of current table
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int table_size = 1 << table_bits; // size of current table
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symbol = 0;
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// Fill in root table.
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for (len = 1, step = 2; len <= root_bits; ++len, step <<= 1)
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{
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num_open <<= 1;
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num_nodes += num_open;
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num_open -= count[len];
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if (num_open < 0)
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return 0;
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for (; count[len] > 0; --count[len])
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{
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HuffmanCode code;
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code.bits = (byte)len;
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code.value = (ushort)sorted[symbol++];
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ReplicateValue (root_table, table + (int)key, step, table_size, code);
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key = GetNextKey (key, len);
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}
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}
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// Fill in 2nd level tables and add pointers to root table.
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for (len = root_bits + 1, step = 2; len <= MaxAllowedCodeLength; ++len, step <<= 1)
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{
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num_open <<= 1;
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num_nodes += num_open;
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num_open -= count[len];
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if (num_open < 0)
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return 0;
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for (; count[len] > 0; --count[len])
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{
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HuffmanCode code;
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if ((key & mask) != low)
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{
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table += table_size;
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table_bits = NextTableBitSize (count, len, root_bits);
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table_size = 1 << table_bits;
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total_size += table_size;
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low = key & mask;
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root_table[index+low].bits = (byte)(table_bits + root_bits);
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root_table[index+low].value = (ushort)(table - index - low);
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}
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code.bits = (byte)(len - root_bits);
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code.value = (ushort)sorted[symbol++];
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ReplicateValue (root_table, table + (int)(key >> root_bits), step, table_size, code);
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key = GetNextKey (key, len);
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}
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}
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// Check if tree is full.
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if (num_nodes != 2 * offset[MaxAllowedCodeLength] - 1)
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return 0;
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return total_size;
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}
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static void ReplicateValue (HuffmanCode[] table, int offset, int step, int end, HuffmanCode code)
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{
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do
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{
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end -= step;
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table[offset+end] = code;
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}
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while (end > 0);
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}
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static int NextTableBitSize (int[] count, int len, int root_bits)
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{
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int left = 1 << (len - root_bits);
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while (len < MaxAllowedCodeLength)
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{
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left -= count[len];
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if (left <= 0) break;
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++len;
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left <<= 1;
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}
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return len - root_bits;
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}
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}
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internal struct HuffmanCode
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{
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public byte bits; // number of bits used for this symbol
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public ushort value; // symbol value or table offset
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}
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internal struct HuffmanCode32
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{
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public int bits; // number of bits used for this symbol,
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// or an impossible value if not a literal code.
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public uint value; // 32b packed ARGB value if literal,
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// or non-literal symbol otherwise
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}
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internal class HTreeGroup
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{
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HuffmanCode[] tables;
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int[] htrees = new int[Huffman.CodesPerMetaCode];
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public bool is_trivial_literal; // True, if huffman trees for Red, Blue & Alpha
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// Symbols are trivial (have a single code).
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public uint literal_arb; // If is_trivial_literal is true, this is the
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// ARGB value of the pixel, with Green channel
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// being set to zero.
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public bool is_trivial_code; // true if is_trivial_literal with only one code
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public bool use_packed_table; // use packed table below for short literal code
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// table mapping input bits to a packed values, or escape case to literal code
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public HuffmanCode32[] packed_table = new HuffmanCode32[Huffman.PackedTableSize];
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public HuffmanCode[] Tables { get { return tables; } }
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public void SetMeta (int meta, int base_index)
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{
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htrees[meta] = base_index;
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}
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public int GetMeta (int meta)
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{
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return htrees[meta];
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}
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public HuffmanCode GetCode (int meta, int index)
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{
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return tables[htrees[meta] + index];
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}
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public void SetCode (int meta, int index, HuffmanCode code)
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{
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tables[htrees[meta] + index] = code;
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}
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public static HTreeGroup[] New (int num_htree_groups, int table_size)
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{
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var tables = new HuffmanCode[num_htree_groups * table_size];
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var htree_groups = new HTreeGroup[num_htree_groups];
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for (int i = 0; i < num_htree_groups; ++i)
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{
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htree_groups[i] = new HTreeGroup();
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htree_groups[i].tables = tables;
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}
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return htree_groups;
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}
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}
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}
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