public StackVirtualMachine(Action <string> errorCallback = null)
{
_memory = new uint[0xFFFF];
_flag = 0;
_sp = 0x0000;
_ip = 0x1000;
_errorCallback = errorCallback;
State = SVMSStates.Active;
}
public void Start()
{
try
{
var instruction = OpCodes.NoOperation;
do
{
if (State == SVMSStates.Active || State == SVMSStates.Step)
{
if (State == SVMSStates.Step)
{
State = SVMSStates.Idle;
}
#region Tick
uint operand1;
uint operand2;
uint result;
instruction = _memory[_ip];
switch (instruction)
{
case OpCodes.Halt:
case OpCodes.NoOperation:
/*
* No operation
*/
break;
case OpCodes.Push:
/*
* Push value onto the stack
*/
Push(GetVal());
break;
case OpCodes.Add:
/*
* Take top 2 operands from the stack, add them, and push the result
* In the event of overflow, set the carry flag
*/
operand1 = Pop();
operand2 = Pop();
result = operand1 + operand2;
if (result < operand1)
{
_flag |= Flags.Carry;
}
CheckForZeroResult(result);
Push(result);
break;
case OpCodes.Subtract:
/*
* Take top 2 operands from the stack, subtract them, and push the result
* In the event of overflow, set the carry flag
*/
operand1 = Pop();
operand2 = Pop();
result = operand1 - operand2;
if (result > operand1)
{
_flag |= Flags.Carry;
}
CheckForZeroResult(result);
Push(result);
break;
case OpCodes.Store:
/*
* Stores operand 2 at address specified by operand 1
*/
_memory[GetVal()] = GetVal();
break;
case OpCodes.JumpToSubroutine:
/*
* Push the instruction pointer onto the stack and jump to address specified by operand 1
*/
operand1 = GetVal();
Push(_ip);
_ip = operand1;
continue;
case OpCodes.Return:
/*
* Returns
*/
_ip = Pop();
break;
case OpCodes.Swap:
/*
* Swaps the top 2 items on the stack
*/
var tmp1 = Pop();
var tmp2 = Pop();
Push(tmp1);
Push(tmp2);
break;
case OpCodes.Compare:
/*
* Compares operand 1 with operand 2, if they are equal, set the Equal flag
* Under the hood it performs a subtraction, and sets the Z flag if it's zero
*/
operand1 = GetVal();
operand2 = GetVal();
result = operand1 - operand2;
CheckForZeroResult(result);
break;
case OpCodes.JumpIfEqual:
/*
* Jump if the Equal flag is set
*/
operand1 = GetVal();
if ((_flag & Flags.Zero) != 0)
{
Push(_ip);
_ip = operand1;
continue;
}
break;
case OpCodes.JumpIfNotEqual:
/*
* Jump if the Equal flag is not set
*/
operand1 = GetVal();
if ((_flag & Flags.Zero) == 0)
{
Push(_ip);
_ip = operand1;
continue;
}
break;
case OpCodes.ClearFlags:
/*
* Clear the flags
*/
_flag = 0;
break;
case OpCodes.Increment:
/*
* Increment the top item on the stack
*/
result = Pop();
++result;
CheckForZeroResult(result);
Push(result);
break;
case OpCodes.Decrement:
/*
* Decrement the top item on the stack
*/
operand1 = Pop();
result = operand1 - 1;
if (result > operand1)
{ // Decremented from zero
result = 1;
_flag |= Flags.Sign;
}
else
{
CheckForZeroResult(result);
}
Push(result);
break;
case OpCodes.Jump:
/*
* jump to address specified by operand 1
*/
operand1 = GetVal();
_ip = operand1;
continue;
default:
throw new InvalidInstructionException($"{instruction.ToString("X")} is not a valid instruction");
}
#endregion
_ip++;
}
} while (instruction != OpCodes.Halt);
}
catch (Exception ex)
{
if (_errorCallback != null)
{
_errorCallback(GetDebugInfo(ex));
}
else
{
throw ex;
}
}
}
