97 lines
3.4 KiB
C#
97 lines
3.4 KiB
C#
//
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// Copyright (c) 2008-2011, Kenneth Bell
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//
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// Permission is hereby granted, free of charge, to any person obtaining a
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// copy of this software and associated documentation files (the "Software"),
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// to deal in the Software without restriction, including without limitation
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// the rights to use, copy, modify, merge, publish, distribute, sublicense,
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// and/or sell copies of the Software, and to permit persons to whom the
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// Software is furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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// DEALINGS IN THE SOFTWARE.
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//
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using System;
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namespace DiscUtils.Compression
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{
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internal sealed class InverseBurrowsWheeler : DataBlockTransform
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{
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private readonly int[] _nextPos;
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private readonly int[] _pointers;
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public InverseBurrowsWheeler(int bufferSize)
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{
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_pointers = new int[bufferSize];
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_nextPos = new int[256];
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}
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protected override bool BuffersMustNotOverlap
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{
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get { return true; }
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}
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public int OriginalIndex { get; set; }
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protected override int DoProcess(byte[] input, int inputOffset, int inputCount, byte[] output, int outputOffset)
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{
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int outputCount = inputCount;
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// First find the frequency of each value
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Array.Clear(_nextPos, 0, _nextPos.Length);
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for (int i = inputOffset; i < inputOffset + inputCount; ++i)
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{
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_nextPos[input[i]]++;
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}
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// We know they're 'sorted' in the first column, so now can figure
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// out the position of the first instance of each.
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int sum = 0;
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for (int i = 0; i < 256; ++i)
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{
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int tempSum = sum;
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sum += _nextPos[i];
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_nextPos[i] = tempSum;
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}
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// For each value in the final column, put a pointer to to the
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// 'next' character in the first (sorted) column.
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for (int i = 0; i < inputCount; ++i)
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{
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_pointers[_nextPos[input[inputOffset + i]]++] = i;
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}
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// The 'next' character after the end of the original string is the
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// first character of the original string.
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int focus = _pointers[OriginalIndex];
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// We can now just walk the pointers to reconstruct the original string
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for (int i = 0; i < outputCount; ++i)
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{
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output[outputOffset + i] = input[inputOffset + focus];
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focus = _pointers[focus];
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}
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return outputCount;
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}
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protected override int MaxOutputCount(int inputCount)
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{
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return inputCount;
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}
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protected override int MinOutputCount(int inputCount)
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{
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return inputCount;
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}
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}
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} |