Attempting to subtract a value will add it instead

[blapaz]

To avoid addition when attempting to subtract, this line stack.Push(value1 + value2); in the else if (opcode == Opcodes.sub) block should be changed to stack.Push(value2 - value1);

else if (opcode == Opcodes.sub)
{
  int value1 = (int) _stack.Pop();
  int value2 = (int) _stack.Pop();
  _stack.Push(value2 - value1);
}