public MachineOperand GetOperand(ImageReader rdr, string args, PrimitiveType dataWidth)
 {
     if (i >= args.Length)
         return null;
     for (; ; )
     {
         if (args[i] == ',')
             ++i;
         Address addr;
         switch (args[i++])
         {
         case 'A':   // Address register A0-A7 encoded in in instrution
             return new RegisterOperand(AddressRegister(opcode, GetOpcodeOffset(args[i++])));
         case 'c':   // CCR register 
             return new RegisterOperand(Registers.ccr);
         case 'D':   // Data register D0-D7 encoded in instruction
             return DataRegisterOperand(opcode, GetOpcodeOffset(args[i++]));
         case 'E':   // Effective address (EA) 
             return ParseOperand(opcode, GetOpcodeOffset(args[i++]), dataWidth, rdr);
         case 'e':   // Effective address with 3-bit halves swapped
             return ParseSwappedOperand(opcode, GetOpcodeOffset(args[i++]), dataWidth, rdr);
         case 'I':   // Immediate operand
             return GetImmediate(rdr, GetSizeType(0, args[i++], dataWidth));
         case 'J':   // PC Relative jump 
             addr = rdr.Address;
             int offset = opcode & 0xFF;
             if (offset == 0xFF)
                 offset = rdr.ReadBeInt32();
             else if (offset == 0x00)
                 offset = rdr.ReadBeInt16();
             else
                 offset = (sbyte) offset;
             return new M68kAddressOperand(addr + offset);
         case 'M':   // Register bitset
             return new RegisterSetOperand(rdr.ReadBeUInt16());
         case 'n':   // cache bitset
             bitSet = rdr.ReadBeUInt16();
             break;
         case 'm':   // Register bitset reversed
             return RegisterSetOperand.CreateReversed(bitSet);
         case 'q':   // "Small" quick constant (3-bit part of the opcode)
             return GetQuickImmediate(GetOpcodeOffset(args[i++]), 0x07, 8, PrimitiveType.Byte);
         case 'Q':   // "Large" quick constant (8-bit part of the opcode)
             return GetQuickImmediate(GetOpcodeOffset(args[i++]), 0xFF, 0, PrimitiveType.SByte);
         case 'R': // relative
             addr = rdr.Address;
             int relative = 0;
             switch (args[i++])
             {
             case 'w': relative = rdr.ReadBeInt16(); break;
             case 'l': relative = rdr.ReadBeInt32(); break;
             default: throw new NotImplementedException();
             }
             return new M68kAddressOperand(addr + relative);
         case 's':   // SR register
             return new RegisterOperand(Registers.sr);
         case '+':   // Postincrement operator; following character specifies bit offset of the address register code.
             return new PostIncrementMemoryOperand(dataWidth, AddressRegister(opcode, GetOpcodeOffset(args[i++])));
         case '-':   // Predecrement operator; following character specifies bit offset of the address register code.
             return new PredecrementMemoryOperand(dataWidth, AddressRegister(opcode, GetOpcodeOffset(args[i++])));
         default: throw new FormatException(string.Format("Unknown argument type {0}.", args[--i]));
         }
     }
 }