public override int GenerateCode(int loc, IVirtualMachine vm, CheckerInformation info)
{
loc = Term.GenerateCode(loc, vm, info);
//Only execute RepTerm if no conditional BoolOpr or if the left hand side is not enough to determine result
if (Operator != Operators.COR && Operator != Operators.CAND)
{
loc = RepTerm.GenerateCode(loc, vm, info);
}
var type = GetExpressionType(info);
if (type == Type.BOOL)
{
switch (Operator)
{
case Operators.AND:
//Can only work with int operations:
//If both terms are true (=1), they result in 2 (1+1=2)
vm.IntAdd(loc++);
//Test if result == 2
vm.IntLoad(loc++, 2);
vm.IntEQ(loc++);
break;
case Operators.OR:
vm.IntAdd(loc++);
vm.IntLoad(loc++, 1);
vm.IntGE(loc++); //>=1 => only one term has to be true
break;
case Operators.CAND:
//If true is on the top of the stack, the second condition has to be evaluated
//1. Jump if left hand side was false
int conditionalJump = loc++;
//2. a. Evaluate right hand side if left hand side was true
loc = RepTerm.GenerateCode(loc, vm, info);
vm.CondJump(conditionalJump, loc + 1); //Step 1: Only now the jump destination is known!
vm.UncondJump(loc, loc + 2);
++loc; //Leap over the load(0) instruction
//2. b. Evaluate to false
vm.IntLoad(loc++, 0);
break;
case Operators.COR:
//If false is on the top of the stack, the second condition has to be evaluated
//1. Invert top of stack:
vm.IntLoad(loc++, 1);
vm.IntNE(loc++);
//2. Jump if left hand side was true
int conditionalJump2 = loc++;
//3. a. Evaluate right hand side if left hand side was false
loc = RepTerm.GenerateCode(loc, vm, info);
vm.CondJump(conditionalJump2, loc + 1);
vm.UncondJump(loc, loc + 2);
++loc;
//3. b. Evaluate to true (without evaluating right hand side)
vm.IntLoad(loc++, 1);
break;
default:
throw new IVirtualMachine.InternalError(
"There's an invalid operator in ASTBoolOpr. Operator: " + Operator.ToString());
}
}
else
{
throw new IVirtualMachine.InternalError(
"There's an invalid operand in ASTBoolOpr. Oprand: " + type.ToString());
}
return(loc);
}