c# - Convert.ChangeType() signed type - changetype

Question

How to convert unsigned integer using the method Convert.ChangeType() if I want to get the number is less than zero ?
Example
uint l = 0xFFF0;
short ret = (short)Convert.ChangeType(l, typeof(short)); // here error instead of -16

Answer 1

I am decided that the problem create own implementation class whith interface IConvertible.
Like this
/// Class that implements IConvertible
class ConvertData : IConvertible
{
public ConvertData(ulong Value)
{
_Field.UlongValue = Value;
}
public ConvertData():this(0)
{
}
public ulong Field
{
set { _Field.UlongValue = value; }
get { return _Field.UlongValue; }
}
ULongStruct _Field;
[StructLayout(LayoutKind.Explicit)]
struct ULongStruct
{
[FieldOffset(0)]
public ulong UlongValue;
[FieldOffset(0)]
public float FloatValue;
[FieldOffset(0)]
public double DoubleValue;
[FieldOffset(0)]
public uint UIntValue;
[FieldOffset(0)]
public int IntValue;
[FieldOffset(0)]
public ushort UShortValue;
[FieldOffset(0)]
public short ShortValue;
[FieldOffset(0)]
public byte ByteValue;
[FieldOffset(0)]
public sbyte SByteValue;
}
public TypeCode GetTypeCode()
{
return TypeCode.Object;
}
bool IConvertible.ToBoolean(IFormatProvider provider)
{
return _Field.ByteValue!=0;
}
byte IConvertible.ToByte(IFormatProvider provider)
{
return _Field.ByteValue;
}
char IConvertible.ToChar(IFormatProvider provider)
{
return (char)_Field.SByteValue;
}
DateTime IConvertible.ToDateTime(IFormatProvider provider)
{
return Convert.ToDateTime(_Field.UlongValue);
}
decimal IConvertible.ToDecimal(IFormatProvider provider)
{
return Convert.ToDecimal(_Field.DoubleValue);
}
double IConvertible.ToDouble(IFormatProvider provider)
{
return _Field.DoubleValue;
}
short IConvertible.ToInt16(IFormatProvider provider)
{
return _Field.ShortValue;
}
int IConvertible.ToInt32(IFormatProvider provider)
{
return _Field.IntValue;
}
long IConvertible.ToInt64(IFormatProvider provider)
{
return (long)_Field.UlongValue;
}
sbyte IConvertible.ToSByte(IFormatProvider provider)
{
return _Field.SByteValue;
}
float IConvertible.ToSingle(IFormatProvider provider)
{
return _Field.FloatValue;
}
string IConvertible.ToString(IFormatProvider provider)
{
return String.Format("({0})", _Field.UlongValue);
}
object IConvertible.ToType(Type conversionType, IFormatProvider provider)
{
return Convert.ChangeType(_Field.UlongValue, conversionType);
}
ushort IConvertible.ToUInt16(IFormatProvider provider)
{
return _Field.UShortValue;
}
uint IConvertible.ToUInt32(IFormatProvider provider)
{
return _Field.UIntValue;
}
ulong IConvertible.ToUInt64(IFormatProvider provider)
{
return _Field.UlongValue;
}
}
Call
ConvertData data = new ConvertData(l);
return (T)Convert.ChangeType(data, typeof(T));