WPinternals/DiscUtils/Ntfs/DataRun.cs

//
// 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.Ntfs
{
    using System.Globalization;
    using System.IO;

    internal class DataRun
    {
        private long _runLength;
        private long _runOffset;
        private bool _isSparse;

        public DataRun()
        {
        }

        public DataRun(long offset, long length, bool isSparse)
        {
            _runOffset = offset;
            _runLength = length;
            _isSparse = isSparse;
        }

        public long RunLength
        {
            get { return _runLength; }
            set { _runLength = value; }
        }

        public long RunOffset
        {
            get { return _runOffset; }
            set { _runOffset = value; }
        }

        public bool IsSparse
        {
            get { return _isSparse; }
        }

        internal int Size
        {
            get
            {
                int runLengthSize = VarLongSize(_runLength);
                int runOffsetSize = VarLongSize(_runOffset);
                return 1 + runLengthSize + runOffsetSize;
            }
        }

        public int Read(byte[] buffer, int offset)
        {
            int runOffsetSize = (buffer[offset] >> 4) & 0x0F;
            int runLengthSize = buffer[offset] & 0x0F;

            _runLength = ReadVarLong(buffer, offset + 1, runLengthSize);
            _runOffset = ReadVarLong(buffer, offset + 1 + runLengthSize, runOffsetSize);
            _isSparse = runOffsetSize == 0;

            return 1 + runLengthSize + runOffsetSize;
        }

        public override string ToString()
        {
            return string.Format(CultureInfo.InvariantCulture, "{0:+##;-##;0}[+{1}]", _runOffset, _runLength);
        }

        internal int Write(byte[] buffer, int offset)
        {
            int runLengthSize = WriteVarLong(buffer, offset + 1, _runLength);
            int runOffsetSize = _isSparse ? 0 : WriteVarLong(buffer, offset + 1 + runLengthSize, _runOffset);

            buffer[offset] = (byte)((runLengthSize & 0x0F) | ((runOffsetSize << 4) & 0xF0));

            return 1 + runLengthSize + runOffsetSize;
        }

        private static long ReadVarLong(byte[] buffer, int offset, int size)
        {
            ulong val = 0;
            bool signExtend = false;

            for (int i = 0; i < size; ++i)
            {
                byte b = buffer[offset + i];
                val = val | (((ulong)b) << (i * 8));
                signExtend = (b & 0x80) != 0;
            }

            if (signExtend)
            {
                for (int i = size; i < 8; ++i)
                {
                    val = val | (((ulong)0xFF) << (i * 8));
                }
            }

            return (long)val;
        }

        private static int WriteVarLong(byte[] buffer, int offset, long val)
        {
            bool isPositive = val >= 0;

            int pos = 0;
            do
            {
                buffer[offset + pos] = (byte)(val & 0xFF);
                val >>= 8;
                pos++;
            }
            while (val != 0 && val != -1);

            // Avoid appearing to have a negative number that is actually positive,
            // record an extra empty byte if needed.
            if (isPositive && (buffer[offset + pos - 1] & 0x80) != 0)
            {
                buffer[offset + pos] = 0;
                pos++;
            }
            else if (!isPositive && (buffer[offset + pos - 1] & 0x80) != 0x80)
            {
                buffer[offset + pos] = 0xFF;
                pos++;
            }

            return pos;
        }

        private static int VarLongSize(long val)
        {
            bool isPositive = val >= 0;
            bool lastByteHighBitSet = false;

            int len = 0;
            do
            {
                lastByteHighBitSet = (val & 0x80) != 0;
                val >>= 8;
                len++;
            }
            while (val != 0 && val != -1);

            if ((isPositive && lastByteHighBitSet) || (!isPositive && !lastByteHighBitSet))
            {
                len++;
            }

            return len;
        }
    }
}