public virtual short read_word(EndianImageReader f)
{
if (!f.IsValid)
{
return(-1);
}
if (!f.IsValidOffset(1))
{
return(-2);
}
return(f.ReadBeInt16());
}
/// <summary>
/// Attempts to decode an operand.
/// </summary>
/// <param name="rdr"></param>
/// <param name="args"></param>
/// <param name="dataWidth"></param>
/// <param name="op"></param>
/// <returns>If true, either no more operands are needed, or an
/// operand was fetched sucessfully. If false, the operand was
/// invalid, either due to a bad encoding or because the reader read
/// off the end of the memory area.
/// </returns>
public bool TryGetOperand(EndianImageReader rdr, string args, PrimitiveType dataWidth, out MachineOperand op)
{
if (i >= args.Length)
{
op = null; return(true);
}
for (; ;)
{
if (args[i] == ',')
{
++i;
}
Address addr;
switch (args[i++])
{
case 'A': // Address register A0-A7 encoded in in instrution
op = new RegisterOperand(AddressRegister(opcode, GetOpcodeOffset(args[i++])));
return(true);
case 'c': // CCR register
op = new RegisterOperand(Registers.ccr);
return(true);
case 'D': // Data register D0-D7 encoded in instruction
op = DataRegisterOperand(opcode, GetOpcodeOffset(args[i++]));
return(true);
case 'E': // Effective address (EA)
return(TryParseOperand(opcode, GetOpcodeOffset(args[i++]), dataWidth, rdr, out op));
case 'e': // Effective address with 3-bit halves swapped
return(TryParseSwappedOperand(opcode, GetOpcodeOffset(args[i++]), dataWidth, rdr, out op));
case 'I': // Immediate operand
return(TryGetImmediate(rdr, GetSizeType(0, args[i++], dataWidth), out op));
case 'J': // PC Relative jump
return(TryPcRelative(rdr, opcode, out op));
case 'M': // Register bitset
var size = GetSizeType(0, args[i++], dataWidth);
op = new RegisterSetOperand(rdr.ReadBeUInt16(), size);
return(true);
case 'n': // cache bitset
bitSet = rdr.ReadBeUInt16();
break;
case 'm': // Register bitset reversed
size = GetSizeType(0, args[i++], dataWidth);
op = RegisterSetOperand.CreateReversed(bitSet, size);
return(true);
case 'q': // "Small" quick constant (3-bit part of the opcode)
op = GetQuickImmediate(GetOpcodeOffset(args[i++]), 0x07, 8, PrimitiveType.Byte);
return(true);
case 'Q': // "Large" quick constant (8-bit part of the opcode)
op = GetQuickImmediate(GetOpcodeOffset(args[i++]), 0xFF, 0, PrimitiveType.SByte);
return(true);
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();
}
op = new M68kAddressOperand(addr + relative);
return(true);
case 's': // SR register
op = new RegisterOperand(Registers.sr);
return(true);
case '+': // Postincrement operator; following character specifies bit offset of the address register code.
op = new PostIncrementMemoryOperand(dataWidth, AddressRegister(opcode, GetOpcodeOffset(args[i++])));
return(true);
case '-': // Predecrement operator; following character specifies bit offset of the address register code.
op = new PredecrementMemoryOperand(dataWidth, AddressRegister(opcode, GetOpcodeOffset(args[i++])));
return(true);
default: throw new FormatException(string.Format("Unknown argument type {0}.", args[--i]));
}
}
}