private Chunk GetChunk(long position, out int chunk, out int block, out int sector)
{
long chunkSize = (1L << 23) * _metadata.LogicalSectorSize;
int chunkRatio = (int)(chunkSize / _metadata.FileParameters.BlockSize);
chunk = (int)(position / chunkSize);
long chunkOffset = position % chunkSize;
block = (int)(chunkOffset / _fileParameters.BlockSize);
int blockOffset = (int)(chunkOffset % _fileParameters.BlockSize);
sector = (int)(blockOffset / _metadata.LogicalSectorSize);
Chunk result = _chunks[chunk];
if (result == null)
{
result = new Chunk(_batStream, _fileStream, _freeSpaceTable, _fileParameters, chunk, chunkRatio);
_chunks[chunk] = result;
}
return result;
}
public override int Read(byte[] buffer, int offset, int count)
{
CheckDisposed();
if (_atEof || _position > _length)
{
_atEof = true;
throw new IOException("Attempt to read beyond end of file");
}
if (_position == _length)
{
_atEof = true;
return(0);
}
if (_position % _metadata.LogicalSectorSize != 0 || count % _metadata.LogicalSectorSize != 0)
{
throw new IOException("Unaligned read");
}
int totalToRead = (int)Math.Min(_length - _position, count);
int totalRead = 0;
while (totalRead < totalToRead)
{
int chunkIndex;
int blockIndex;
int sectorIndex;
Chunk chunk = GetChunk(_position + totalRead, out chunkIndex, out blockIndex, out sectorIndex);
int blockOffset = (int)(sectorIndex * _metadata.LogicalSectorSize);
int blockBytesRemaining = (int)(_fileParameters.BlockSize - blockOffset);
PayloadBlockStatus blockStatus = chunk.GetBlockStatus(blockIndex);
if (blockStatus == PayloadBlockStatus.FullyPresent)
{
_fileStream.Position = chunk.GetBlockPosition(blockIndex) + blockOffset;
int read = StreamUtilities.ReadMaximum(_fileStream, buffer, offset + totalRead,
Math.Min(blockBytesRemaining, totalToRead - totalRead));
totalRead += read;
}
else if (blockStatus == PayloadBlockStatus.PartiallyPresent)
{
BlockBitmap bitmap = chunk.GetBlockBitmap(blockIndex);
bool present;
int numSectors = bitmap.ContiguousSectors(sectorIndex, out present);
int toRead = (int)Math.Min(numSectors * _metadata.LogicalSectorSize, totalToRead - totalRead);
int read;
if (present)
{
_fileStream.Position = chunk.GetBlockPosition(blockIndex) + blockOffset;
read = StreamUtilities.ReadMaximum(_fileStream, buffer, offset + totalRead, toRead);
}
else
{
_parentStream.Position = _position + totalRead;
read = StreamUtilities.ReadMaximum(_parentStream, buffer, offset + totalRead, toRead);
}
totalRead += read;
}
else if (blockStatus == PayloadBlockStatus.NotPresent)
{
_parentStream.Position = _position + totalRead;
int read = StreamUtilities.ReadMaximum(_parentStream, buffer, offset + totalRead,
Math.Min(blockBytesRemaining, totalToRead - totalRead));
totalRead += read;
}
else
{
int zeroed = Math.Min(blockBytesRemaining, totalToRead - totalRead);
Array.Clear(buffer, offset + totalRead, zeroed);
totalRead += zeroed;
}
}
_position += totalRead;
return(totalRead);
}
