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Initial commit - WPinternals 2.6
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Rene Lergner
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//
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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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namespace DiscUtils
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{
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using System;
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using System.Collections.Generic;
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/// <summary>
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/// A sparse in-memory buffer.
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/// </summary>
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/// <remarks>This class is useful for storing large sparse buffers in memory, unused
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/// chunks of the buffer are not stored (assumed to be zero).</remarks>
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public sealed class SparseMemoryBuffer : Buffer
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{
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private Dictionary<int, byte[]> _buffers;
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private int _chunkSize;
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private long _capacity;
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/// <summary>
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/// Initializes a new instance of the SparseMemoryBuffer class.
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/// </summary>
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/// <param name="chunkSize">The size of each allocation chunk.</param>
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public SparseMemoryBuffer(int chunkSize)
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{
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_chunkSize = chunkSize;
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_buffers = new Dictionary<int, byte[]>();
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}
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/// <summary>
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/// Indicates this stream can be read (always <c>true</c>).
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/// </summary>
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public override bool CanRead
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{
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get { return true; }
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}
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/// <summary>
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/// Indicates this stream can be written (always <c>true</c>).
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/// </summary>
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public override bool CanWrite
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{
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get { return true; }
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}
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/// <summary>
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/// Gets the current capacity of the sparse buffer (number of logical bytes stored).
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/// </summary>
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public override long Capacity
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{
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get { return _capacity; }
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}
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/// <summary>
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/// Gets the size of each allocation chunk.
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/// </summary>
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public int ChunkSize
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{
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get { return _chunkSize; }
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}
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/// <summary>
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/// Gets the (sorted) list of allocated chunks, as chunk indexes.
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/// </summary>
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/// <returns>An enumeration of chunk indexes.</returns>
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/// <remarks>This method returns chunks as an index rather than absolute stream position.
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/// For example, if ChunkSize is 16KB, and the first 32KB of the buffer is actually stored,
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/// this method will return 0 and 1. This indicates the first and second chunks are stored.</remarks>
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public IEnumerable<int> AllocatedChunks
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{
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get
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{
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List<int> keys = new List<int>(_buffers.Keys);
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keys.Sort();
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return keys;
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}
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}
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/// <summary>
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/// Accesses this memory buffer as an infinite byte array.
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/// </summary>
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/// <param name="pos">The buffer position to read.</param>
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/// <returns>The byte stored at this position (or Zero if not explicitly stored).</returns>
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public byte this[long pos]
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{
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get
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{
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byte[] buffer = new byte[1];
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if (Read(pos, buffer, 0, 1) != 0)
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{
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return buffer[0];
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}
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else
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{
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return 0;
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}
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}
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set
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{
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byte[] buffer = new byte[1];
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buffer[0] = value;
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Write(pos, buffer, 0, 1);
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}
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}
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/// <summary>
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/// Reads a section of the sparse buffer into a byte array.
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/// </summary>
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/// <param name="pos">The offset within the sparse buffer to start reading.</param>
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/// <param name="buffer">The destination byte array.</param>
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/// <param name="offset">The start offset within the destination buffer.</param>
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/// <param name="count">The number of bytes to read.</param>
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/// <returns>The actual number of bytes read.</returns>
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public override int Read(long pos, byte[] buffer, int offset, int count)
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{
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int totalRead = 0;
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while (totalRead < count && pos < _capacity)
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{
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int chunk = (int)(pos / _chunkSize);
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int chunkOffset = (int)(pos % _chunkSize);
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int numToRead = (int)Math.Min(Math.Min(_chunkSize - chunkOffset, _capacity - pos), count - totalRead);
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byte[] chunkBuffer;
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if (!_buffers.TryGetValue(chunk, out chunkBuffer))
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{
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Array.Clear(buffer, offset + totalRead, numToRead);
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}
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else
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{
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Array.Copy(chunkBuffer, chunkOffset, buffer, offset + totalRead, numToRead);
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}
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totalRead += numToRead;
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pos += numToRead;
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}
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return totalRead;
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}
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/// <summary>
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/// Writes a byte array into the sparse buffer.
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/// </summary>
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/// <param name="pos">The start offset within the sparse buffer.</param>
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/// <param name="buffer">The source byte array.</param>
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/// <param name="offset">The start offset within the source byte array.</param>
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/// <param name="count">The number of bytes to write.</param>
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public override void Write(long pos, byte[] buffer, int offset, int count)
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{
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int totalWritten = 0;
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while (totalWritten < count)
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{
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int chunk = (int)(pos / _chunkSize);
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int chunkOffset = (int)(pos % _chunkSize);
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int numToWrite = (int)Math.Min(_chunkSize - chunkOffset, count - totalWritten);
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byte[] chunkBuffer;
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if (!_buffers.TryGetValue(chunk, out chunkBuffer))
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{
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chunkBuffer = new byte[_chunkSize];
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_buffers[chunk] = chunkBuffer;
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}
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Array.Copy(buffer, offset + totalWritten, chunkBuffer, chunkOffset, numToWrite);
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totalWritten += numToWrite;
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pos += numToWrite;
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}
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_capacity = Math.Max(_capacity, pos);
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}
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/// <summary>
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/// Sets the capacity of the sparse buffer, truncating if appropriate.
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/// </summary>
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/// <param name="value">The desired capacity of the buffer.</param>
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/// <remarks>This method does not allocate any chunks, it merely records the logical
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/// capacity of the sparse buffer. Writes beyond the specified capacity will increase
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/// the capacity.</remarks>
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public override void SetCapacity(long value)
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{
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_capacity = value;
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}
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/// <summary>
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/// Gets the parts of a buffer that are stored, within a specified range.
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/// </summary>
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/// <param name="start">The offset of the first byte of interest.</param>
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/// <param name="count">The number of bytes of interest.</param>
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/// <returns>An enumeration of stream extents, indicating stored bytes.</returns>
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public override IEnumerable<StreamExtent> GetExtentsInRange(long start, long count)
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{
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long end = start + count;
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foreach (var chunk in AllocatedChunks)
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{
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long chunkStart = chunk * (long)_chunkSize;
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long chunkEnd = chunkStart + _chunkSize;
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if (chunkEnd > start && chunkStart < end)
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{
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long extentStart = Math.Max(start, chunkStart);
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yield return new StreamExtent(extentStart, Math.Min(chunkEnd, end) - extentStart);
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}
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}
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}
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}
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}
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