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using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace PointerTest
{
    public unsafe struct ObjectPointer<T> where T : class
    {
        private readonly SharedData _sharedData;
        private readonly int _offset;

        public T Target
        {
            get { return _sharedData.Target; }
        }

        public byte ByteValue
        {
            get
            {
                Debug.Assert(_sharedData.BasePtr != null);
                return *(_sharedData.BasePtr + _offset);
            }
            set
            {
                Debug.Assert(_sharedData.BasePtr != null);
                *(_sharedData.BasePtr + _offset) = value;
            }
        }

        public int Int32Value
        {
            get
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 4 <= _sharedData.Size);
                return *((int*)(_sharedData.BasePtr + _offset));
            }
            set
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 4 <= _sharedData.Size);
                *((int*)(_sharedData.BasePtr + _offset)) = value;
            }
        }

        public uint UInt32Value
        {
            get
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 4 <= _sharedData.Size);
                return *((uint*)(_sharedData.BasePtr + _offset));
            }
            set
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 4 <= _sharedData.Size);
                *((uint*)(_sharedData.BasePtr + _offset)) = value;
            }
        }

        public short Int16Value
        {
            get
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 2 <= _sharedData.Size);
                return *((short*)(_sharedData.BasePtr + _offset));
            }
            set
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 2 <= _sharedData.Size);
                *((short*)(_sharedData.BasePtr + _offset)) = value;
            }
        }

        public ushort UInt16Value
        {
            get
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 2 <= _sharedData.Size);
                return *((ushort*)(_sharedData.BasePtr + _offset));
            }
            set
            {
                Debug.Assert(_sharedData.BasePtr != null && _offset + 2 <= _sharedData.Size);
                *((ushort*)(_sharedData.BasePtr + _offset)) = value;
            }
        }

        public ObjectPointer(T managedObject)
        {
            var gcHandle = default(GCHandle);

            if (managedObject != null)
                gcHandle = GCHandle.Alloc(managedObject, GCHandleType.Pinned);

            _sharedData = new SharedData(managedObject, gcHandle);
            _offset = 0;
        }

        private ObjectPointer(SharedData sharedData, int offset)
        {
            _offset = offset;
            _sharedData = sharedData;

            Debug.Assert(offset >= 0);
            Debug.Assert(offset == 0 || _sharedData != null && offset < _sharedData.Size);
        }

        public static ObjectPointer<T> operator +(ObjectPointer<T> a, int count)
        {
            return new ObjectPointer<T>(a._sharedData, a._offset + count);
        }

        public static ObjectPointer<T> operator -(ObjectPointer<T> a, int count)
        {
            return new ObjectPointer<T>(a._sharedData, a._offset - count);
        }

        public static ObjectPointer<T> operator ++(ObjectPointer<T> a)
        {
            return new ObjectPointer<T>(a._sharedData, a._offset + 1);
        }

        public static ObjectPointer<T> operator --(ObjectPointer<T> a)
        {
            return new ObjectPointer<T>(a._sharedData, a._offset - 1);
        }

        public bool IsNull
        {
            get { return _sharedData.BasePtr == null; }
        }

        public static bool operator <(ObjectPointer<T> a, ObjectPointer<T> b)
        {
            Debug.Assert(ReferenceEquals(a._sharedData, b._sharedData));
            return a._offset < b._offset;
        }

        public static bool operator >(ObjectPointer<T> a, ObjectPointer<T> b)
        {
            Debug.Assert(ReferenceEquals(a._sharedData, b._sharedData));
            return a._offset > b._offset;
        }

        public static bool operator <=(ObjectPointer<T> a, ObjectPointer<T> b)
        {
            Debug.Assert(ReferenceEquals(a._sharedData, b._sharedData));
            return a._offset <= b._offset;
        }

        public static bool operator >=(ObjectPointer<T> a, ObjectPointer<T> b)
        {
            Debug.Assert(ReferenceEquals(a._sharedData, b._sharedData));
            return a._offset >= b._offset;
        }

        public static implicit operator ObjectPointer<T>(T x)
        {
            return new ObjectPointer<T>(x);
        }

        public static bool operator ==(ObjectPointer<T> x, ObjectPointer<T> y)
        {
            return x._sharedData == y._sharedData && x._offset == y._offset;
        }

        public static bool operator !=(ObjectPointer<T> x, ObjectPointer<T> y)
        {
            return !(x == y);
        }

        public override bool Equals(object x)
        {
            if (x == null)
                return this._sharedData == null;

            var ptr = x as ObjectPointer<T>?;
            if (!ptr.HasValue)
                return false;

            return this == ptr.Value;
        }

        public override int GetHashCode()
        {
            unchecked
            {
                var hash = this._sharedData.GetHashCode();
                return hash + this._offset;
            }
        }

        public byte this[int index]
        {
            get
            {
                var offset = _offset + index;
                Debug.Assert(offset >= 0 && offset < _sharedData.Size);
                return *(_sharedData.BasePtr + offset);
            }
            set
            {
                var offset = _offset + index;
                Debug.Assert(offset >= 0 && offset < _sharedData.Size);
                *(_sharedData.BasePtr + offset) = value;
            }
        }

        #region SharedData Class

        private sealed class SharedData
        {
            private readonly T _target;
            private readonly byte* _basePtr;
            private readonly int _size;
            private readonly GCHandle _handle;

            public SharedData(T target, GCHandle handle)
            {
                _target = target;
                _handle = handle;
                _basePtr = handle.IsAllocated ? (byte*)handle.AddrOfPinnedObject() : null;
                _size = Marshal.SizeOf(typeof(T));
            }

            public byte* BasePtr
            {
                get { return _basePtr; }
            }

            public int Size
            {
                get { return _size; }
            }

            public T Target
            {
                get { return _target; }
            }

            ~SharedData()
            {
                if (_handle.IsAllocated)
                    _handle.Free();
            }
        }

        #endregion
    }

    [StructLayout(LayoutKind.Explicit)]
    public class TestClass
    {
        [FieldOffset(0)] public byte A;
        [FieldOffset(1)] public byte B;
        [FieldOffset(2)] public byte C;
        [FieldOffset(3)] public byte D;
        [FieldOffset(4)] public uint E;

        public override string ToString()
        {
            return string.Format("A: 0x{0:X00}, B: 0x{1:X00}, C: 0x{2:X00}, D: 0x{3:X00}, E: 0x{4:X8}", A, B, C, D, E);
        }

    }

    class Program
    {
        static void Main()
        {
            var o = new TestClass { A = 0x1F, B = 0x3F, C = 0x7F, D = 0xFF, E = 0 };
            var pinned = new ObjectPointer<TestClass>(o);
            var p = pinned;

            Console.WriteLine(o);

            p[0] = 0xDE;
            ++p;
            p.ByteValue = 0xAD;
            ++p;
            p[0] = 0xBE;
            p[1] = 0xEF;

            Console.WriteLine(o);

            p -= 2;
            p.UInt32Value = 0xFFFFFFFF;

            Console.WriteLine(o);

            p += 4;
            p.UInt32Value = 0xDEADBEEF;

            Console.WriteLine(o);
        }
    }
}