private Variable ReadVariable(ref int address)
{
return(Variable.FromByte(memory.ReadByte(ref address)));
}
public Instruction NextInstruction()
{
var startAddress = address;
Instruction instruction;
if (cache.TryGet(startAddress, out instruction))
{
address += instruction.Length;
return(instruction);
}
var opByte = memory.ReadByte(ref address);
Opcode opcode;
for (int i = 0; i < 8; i++)
{
operandKinds[i] = opKind_Omitted;
}
if (opByte >= 0x00 && opByte <= 0x1f)
{
opcode = opcodeTable[OpcodeKind.TwoOp, LongForm(opByte)];
operandKinds[0] = opKind_SmallConstant;
operandKinds[1] = opKind_SmallConstant;
}
else if (opByte >= 0x20 && opByte <= 0x3f)
{
opcode = opcodeTable[OpcodeKind.TwoOp, LongForm(opByte)];
operandKinds[0] = opKind_SmallConstant;
operandKinds[1] = opKind_Variable;
}
else if (opByte >= 0x40 && opByte <= 0x5f)
{
opcode = opcodeTable[OpcodeKind.TwoOp, LongForm(opByte)];
operandKinds[0] = opKind_Variable;
operandKinds[1] = opKind_SmallConstant;
}
else if (opByte >= 0x60 && opByte <= 0x7f)
{
opcode = opcodeTable[OpcodeKind.TwoOp, LongForm(opByte)];
operandKinds[0] = opKind_Variable;
operandKinds[1] = opKind_Variable;
}
else if (opByte >= 0x80 && opByte <= 0x8f)
{
opcode = opcodeTable[OpcodeKind.OneOp, ShortForm(opByte)];
operandKinds[0] = opKind_LargeConstant;
}
else if (opByte >= 0x90 && opByte <= 0x9f)
{
opcode = opcodeTable[OpcodeKind.OneOp, ShortForm(opByte)];
operandKinds[0] = opKind_SmallConstant;
}
else if (opByte >= 0xa0 && opByte <= 0xaf)
{
opcode = opcodeTable[OpcodeKind.OneOp, ShortForm(opByte)];
operandKinds[0] = opKind_Variable;
}
else if ((opByte >= 0xb0 && opByte <= 0xbd) || opByte == 0xbf)
{
opcode = opcodeTable[OpcodeKind.ZeroOp, ShortForm(opByte)];
}
else if (opByte == 0xbe)
{
opcode = opcodeTable[OpcodeKind.Ext, memory.ReadByte(ref address)];
ReadOperandKinds();
}
else if (opByte >= 0xc0 && opByte <= 0xdf)
{
opcode = opcodeTable[OpcodeKind.TwoOp, VarForm(opByte)];
ReadOperandKinds();
}
else // opByte >= 0xe0 && opByte <= 0xff
{
opcode = opcodeTable[OpcodeKind.VarOp, VarForm(opByte)];
ReadOperandKinds();
}
if (opcode.IsDoubleVariable)
{
ReadOperandKinds(4);
}
var operands = ReadOperands();
Variable storeVariable = null;
if (opcode.HasStoreVariable)
{
storeVariable = ReadVariable(ref address);
}
Branch?branch = null;
if (opcode.HasBranch)
{
branch = ReadBranch(ref address);
}
ushort[] ztext = null;
if (opcode.HasZText)
{
ztext = ReadZWords(ref address);
}
var length = address - startAddress;
instruction = new Instruction(startAddress, length, opcode, operands, operands.Length, storeVariable, branch, ztext);
cache.Add(startAddress, instruction);
return(instruction);
}