LibHac/libhac.Nand/DiscUtils.Core/Compression/HuffmanTree.cs

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2018-07-09 18:49:59 +02:00
//
// Copyright (c) 2008-2011, Kenneth Bell
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//
namespace DiscUtils.Compression
{
/// <summary>
/// A canonical Huffman tree implementation.
/// </summary>
/// <remarks>
/// A lookup table is created that will take any bit sequence (max tree depth in length),
/// indicating the output symbol. In WIM files, in practice, no chunk exceeds 32768 bytes
/// in length, so we often end up generating a bigger lookup table than the data it's
/// encoding. This makes for exceptionally fast symbol lookups O(1), but is inefficient
/// overall.
/// </remarks>
internal sealed class HuffmanTree
{
private readonly uint[] _buffer;
private readonly int _numBits; // Max bits per symbol
private readonly int _numSymbols; // Max symbols
public HuffmanTree(uint[] lengths)
{
Lengths = lengths;
_numSymbols = lengths.Length;
uint maxLength = 0;
for (int i = 0; i < Lengths.Length; ++i)
{
if (Lengths[i] > maxLength)
{
maxLength = Lengths[i];
}
}
_numBits = (int)maxLength;
_buffer = new uint[1 << _numBits];
Build();
}
public uint[] Lengths { get; }
public uint NextSymbol(BitStream bitStream)
{
uint symbol = _buffer[bitStream.Peek(_numBits)];
// We may have over-read, reset bitstream position
bitStream.Consume((int)Lengths[symbol]);
return symbol;
}
private void Build()
{
int position = 0;
// For each bit-length...
for (int i = 1; i <= _numBits; ++i)
{
// Check each symbol
for (uint symbol = 0; symbol < _numSymbols; ++symbol)
{
if (Lengths[symbol] == i)
{
int numToFill = 1 << (_numBits - i);
for (int n = 0; n < numToFill; ++n)
{
_buffer[position + n] = symbol;
}
position += numToFill;
}
}
}
for (int i = position; i < _buffer.Length; ++i)
{
_buffer[i] = uint.MaxValue;
}
}
}
}