private ushort GetOperand(ParsedInstruction currentLine, out Error error)
{
if (currentLine.operandExpression == null)
{
error = Error.None;
return(currentLine.operandValue.Value);
}
if (currentLine.operandExpression != null)
{
StringSection expression = currentLine.operandExpression;
var result = Assembler.Evaluator.EvaluateExpression(ref expression, currentLine.sourceLine, out error).Value;
if (error.Code != ErrorCode.None)
{
error = new Error(error, currentLine.sourceLine);
return(0);
}
else if (!expression.IsNullOrEmpty)
{
error = new Error(ErrorCode.Invalid_Expression, Error.Msg_InvalidExpression, currentLine.sourceLine);
return(0);
}
return(result);
}
error = new Error(ErrorCode.Engine_Error, "Instruction required an operand, but none was present. Instruction may have been mis-parsed.", currentLine.sourceLine);
return(0);
}
// Todo: Move TryToConvertToZeroPage and FindOpcode to another class, probably assembler.
// (The only reason they need to be instance methods is for AllowInvalidOpcodes, but this
// could also be specified as a parameter).
public bool TryToConvertToZeroPage(ref ParsedInstruction instruction)
{
var op = Opcode.allOps[instruction.opcode];
var addressing = op.addressing;
Opcode.addressing newAddressing = addressing;
switch (addressing)
{
case Opcode.addressing.absolute:
newAddressing = Opcode.addressing.zeropage;
break;
case Opcode.addressing.absoluteIndexedX:
newAddressing = Opcode.addressing.zeropageIndexedX;
break;
case Opcode.addressing.absoluteIndexedY:
newAddressing = Opcode.addressing.zeropageIndexedY;
break;
}
if (addressing == newAddressing)
{
return(false);
}
int newOpcode = FindOpcode(op.name, newAddressing);
if (newOpcode >= 0)
{
instruction = new ParsedInstruction(instruction, (byte)newOpcode);
return(true);
}
return(false);
}
static ParsedInstruction()
{
Empty = new ParsedInstruction(0xFF, null, -1);
}
public ParsedInstruction(ParsedInstruction oldLine, byte newOpcode)
{
this = oldLine; // Does this work?
this.opcode = newOpcode;
}