/// <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]));
}
}
}
private bool TryParseOperandInner(byte addressMode, byte operandBits, PrimitiveType dataWidth, EndianImageReader rdr, out MachineOperand op)
{
Constant offset;
switch (addressMode)
{
case 0: // Data register direct.
op = DataRegisterOperand(operandBits, 0);
return(true);
case 1: // Address register direct
op = new RegisterOperand(AddressRegister(operandBits, 0));
return(true);
case 2: // Address register indirect
op = MemoryOperand.Indirect(dataWidth, AddressRegister(operandBits, 0));
return(true);
case 3: // Address register indirect with postincrement.
op = MemoryOperand.PostIncrement(dataWidth, AddressRegister(operandBits, 0));
return(true);
case 4: // Address register indirect with predecrement.
op = MemoryOperand.PreDecrement(dataWidth, AddressRegister(operandBits, 0));
return(true);
case 5: // Address register indirect with displacement.
if (!rdr.TryReadBe(PrimitiveType.Int16, out offset))
{
op = null;
return(false);
}
op = MemoryOperand.Indirect(dataWidth, AddressRegister(operandBits, 0), offset);
return(true);
case 6: // Address register indirect with index
return(TryAddressRegisterIndirectWithIndex(dataWidth, rdr, out op));
case 7:
switch (operandBits)
{
case 0: // Absolute short address
ushort usAddr;
if (!rdr.TryReadBeUInt16(out usAddr))
{
op = null; return(false);
}
op = new M68kAddressOperand(usAddr);
return(true);
case 1: // Absolute long address
uint uAddr;
if (!rdr.TryReadBeUInt32(out uAddr))
{
op = null; return(false);
}
op = new M68kAddressOperand(uAddr);
return(true);
case 2: // Program counter with displacement
var off = rdr.Address - dasm.instr.Address;
short sOffset;
if (!rdr.TryReadBeInt16(out sOffset))
{
op = null; return(false);
}
off += sOffset;
op = new MemoryOperand(dataWidth, Registers.pc, Constant.Int16((short)off));
return(true);
case 3:
// Program counter with index
var addrExt = rdr.Address;
ushort extension = rdr.ReadBeUInt16();
if (EXT_FULL(extension))
{
if (EXT_EFFECTIVE_ZERO(extension))
{
op = new M68kImmediateOperand(Constant.Word32(0));
return(true);
}
Constant @base = null;
Constant outer = null;
if (EXT_BASE_DISPLACEMENT_PRESENT(extension))
{
@base = EXT_BASE_DISPLACEMENT_LONG(extension)
? rdr.ReadBe(PrimitiveType.Word32)
: rdr.ReadBe(PrimitiveType.Int16);
}
if (EXT_OUTER_DISPLACEMENT_PRESENT(extension))
{
outer = EXT_OUTER_DISPLACEMENT_LONG(extension)
? rdr.ReadBe(PrimitiveType.Word32)
: rdr.ReadBe(PrimitiveType.Int16);
}
RegisterStorage base_reg = EXT_BASE_REGISTER_PRESENT(extension)
? Registers.pc
: null;
RegisterStorage index_reg = null;
PrimitiveType index_width = null;
int index_scale = 0;
if (EXT_INDEX_REGISTER_PRESENT(extension))
{
index_reg = EXT_INDEX_AR(extension)
? Registers.AddressRegister((int)EXT_INDEX_REGISTER(extension))
: Registers.DataRegister((int)EXT_INDEX_REGISTER(extension));
index_width = EXT_INDEX_LONG(extension) ? PrimitiveType.Word32 : PrimitiveType.Int16;
index_scale = (EXT_INDEX_SCALE(extension) != 0)
? 1 << EXT_INDEX_SCALE(extension)
: 0;
}
op = new IndexedOperand(dataWidth, @base, outer, base_reg, index_reg, index_width, index_scale,
(extension & 7) > 0 && (extension & 7) < 4,
(extension & 7) > 4);
return(true);
}
op = new IndirectIndexedOperand(
dataWidth,
EXT_8BIT_DISPLACEMENT(extension),
Registers.pc,
EXT_INDEX_AR(extension)
? Registers.AddressRegister((int)EXT_INDEX_REGISTER(extension))
: Registers.DataRegister((int)EXT_INDEX_REGISTER(extension)),
EXT_INDEX_LONG(extension)
? PrimitiveType.Word32
: PrimitiveType.Int16,
1 << EXT_INDEX_SCALE(extension));
return(true);
case 4:
// Immediate
if (dataWidth.Size == 1) // don't want the instruction stream to get misaligned!
{
rdr.Offset += 1;
}
Constant coff;
if (!rdr.TryReadBe(dataWidth, out coff))
{
op = null; return(false);
}
op = new M68kImmediateOperand(coff);
return(true);
default:
op = null;
return(false);
}
default:
throw new NotImplementedException(string.Format("Address mode {0:X1} not implemented.", addressMode));
}
}