private uint DecodeStoreOperand(Opcode opcode, byte type, ref uint operandPos)
{
uint address;
switch (type)
{
case 0:
// discard result
WriteTrace("discard");
return 0;
// case 1..4: unused
case 5:
address = image.ReadByte(operandPos++);
WriteTrace("ptr_" + address.ToString());
break;
case 6:
address = image.ReadInt16(operandPos);
operandPos += 2;
WriteTrace("ptr_" + address.ToString());
break;
case 7:
address = image.ReadInt32(operandPos);
operandPos += 4;
WriteTrace("ptr_" + address.ToString());
break;
// case 8: push onto stack
case 8:
// push onto stack
WriteTrace("sp");
return 0;
case 9:
address = image.ReadByte(operandPos++);
WriteTrace("local_" + address.ToString());
break;
case 10:
address = image.ReadInt16(operandPos);
operandPos += 2;
WriteTrace("local_" + address.ToString());
break;
case 11:
address = image.ReadInt32(operandPos);
operandPos += 4;
WriteTrace("local_" + address.ToString());
break;
// case 12: unused
case 13:
address = image.RamStart + image.ReadByte(operandPos++);
WriteTrace("ram_" + (address - image.RamStart).ToString());
break;
case 14:
address = image.RamStart + image.ReadInt16(operandPos);
operandPos += 2;
WriteTrace("ram_" + (address - image.RamStart).ToString());
break;
case 15:
address = image.RamStart + image.ReadInt32(operandPos);
operandPos += 4;
WriteTrace("ram_" + (address - image.RamStart).ToString());
break;
default:
throw new ArgumentException("Invalid operand type");
}
return address;
}
private uint DecodeLoadOperand(Opcode opcode, byte type, ref uint operandPos)
{
uint address, value;
switch (type)
{
case 0:
WriteTrace("zero");
return 0;
case 1:
value = (uint)(sbyte)image.ReadByte(operandPos++);
WriteTrace("byte_" + value.ToString());
return value;
case 2:
operandPos += 2;
value = (uint)(short)image.ReadInt16(operandPos - 2);
WriteTrace("short_" + value.ToString());
return value;
case 3:
operandPos += 4;
value = image.ReadInt32(operandPos - 4);
WriteTrace("int_" + value.ToString());
return value;
// case 4: unused
case 5:
address = image.ReadByte(operandPos++);
WriteTrace("ptr");
goto LoadIndirect;
case 6:
address = image.ReadInt16(operandPos);
operandPos += 2;
WriteTrace("ptr");
goto LoadIndirect;
case 7:
address = image.ReadInt32(operandPos);
operandPos += 4;
WriteTrace("ptr");
LoadIndirect:
WriteTrace("_" + address.ToString() + "(");
switch (opcode.Attr.Rule)
{
case OpcodeRule.Indirect8Bit:
value = image.ReadByte(address);
break;
case OpcodeRule.Indirect16Bit:
value = image.ReadInt16(address);
break;
default:
value = image.ReadInt32(address);
break;
}
WriteTrace(value.ToString() + ")");
return value;
case 8:
if (sp <= fp + frameLen)
throw new VMException("Stack underflow");
value = Pop();
WriteTrace("sp(" + value.ToString() + ")");
return value;
case 9:
address = image.ReadByte(operandPos++);
goto LoadLocal;
case 10:
address = image.ReadInt16(operandPos);
operandPos += 2;
goto LoadLocal;
case 11:
address = image.ReadInt32(operandPos);
operandPos += 4;
LoadLocal:
WriteTrace("local_" + address.ToString() + "(");
address += fp + localsPos;
switch (opcode.Attr.Rule)
{
case OpcodeRule.Indirect8Bit:
if (address >= fp + frameLen)
throw new VMException("Reading outside local storage bounds");
else
value = stack[address];
break;
case OpcodeRule.Indirect16Bit:
if (address + 1 >= fp + frameLen)
throw new VMException("Reading outside local storage bounds");
else
value = BigEndian.ReadInt16(stack, address);
break;
default:
if (address + 3 >= fp + frameLen)
throw new VMException("Reading outside local storage bounds");
else
value = ReadFromStack(address);
break;
}
WriteTrace(value.ToString() + ")");
return value;
// case 12: unused
case 13:
address = image.RamStart + image.ReadByte(operandPos++);
WriteTrace("ram");
goto LoadIndirect;
case 14:
address = image.RamStart + image.ReadInt16(operandPos);
operandPos += 2;
WriteTrace("ram");
goto LoadIndirect;
case 15:
address = image.RamStart + image.ReadInt32(operandPos);
operandPos += 4;
WriteTrace("ram");
goto LoadIndirect;
default:
throw new ArgumentException("Invalid operand type");
}
}