public override void Assignment(Token varName, bool withArrayIndex)
{
//This is slightly tricky. We need to have the address of the
//variable to which we're doing the assignment on the stack,
//and then everything is really easy. If it's an array, we need
//the address of the array element to which we're doing the
//assignment (its index is on the stack following the LHS value).
if (MethodSymTable.HasSymbol(varName.Value))
{
Symbol symbol = MethodSymTable.GetSymbol(varName.Value);
Contract.Assert(symbol.Kind == SymbolKind.Local ||
symbol.Kind == SymbolKind.Parameter);
Output.WriteLine(" __PUSH((__WORD)&{0});", symbol.Name);
}
else
{
Contract.Assert(ClassSymTable.HasSymbol(varName.Value));
Symbol symbol = ClassSymTable.GetSymbol(varName.Value);
if (symbol.Kind == SymbolKind.Static)
{
Output.WriteLine(" __PUSH((__WORD)&{0});", FormatStaticName(symbol.Name));
}
else if (symbol.Kind == SymbolKind.Field)
{
Output.WriteLine(" __PUSH((__WORD)&((({0}*)THIS)->{1}));", _currentClassName, symbol.Name);
}
}
//If it's an array, obtain the address of the right element by
//adding the index which is on the stack. We need a scratch
//location because issuing two __POP() calls in the same statement
//does not guarantee left-to-right evaluation.
if (withArrayIndex)
{
//The array address is now on the stack, but we really need the
//address of the first element. Hence the dereference:
Output.WriteLine(" __SCRATCH2 = *(__WORD*)__POP();");
//This is the RHS value that we ought to put in the array element:
Output.WriteLine(" __SCRATCH1 = __POP();");
//Finally, the top of the stack contains the value of the array
//indexing expression, i.e. the element index:
Output.WriteLine(" * ( ((__WORD*)__SCRATCH2) + __POP() ) = __SCRATCH1;");
}
else
{
Output.WriteLine(" __SCRATCH1 = __POP();"); //This is the LHS
Output.WriteLine(" * ((__WORD*)__SCRATCH1) = __POP();");
}
}
public override void VariableRead(Token varName, bool withArrayIndex)
{
//Put the value of the variable on the top of the stack. If it's
//an array, the value is the address of the array's first element.
if (MethodSymTable.HasSymbol(varName.Value))
{
Symbol symbol = MethodSymTable.GetSymbol(varName.Value);
Contract.Assert(symbol.Kind == SymbolKind.Local ||
symbol.Kind == SymbolKind.Parameter);
Output.WriteLine(" __PUSH({0});", symbol.Name);
}
else
{
Contract.Assert(ClassSymTable.HasSymbol(varName.Value));
Symbol symbol = ClassSymTable.GetSymbol(varName.Value);
if (symbol.Kind == SymbolKind.Static)
{
Output.WriteLine(" __PUSH({0});", FormatStaticName(symbol.Name));
}
else if (symbol.Kind == SymbolKind.Field)
{
Output.WriteLine(" __PUSH((({0}*)THIS)->{1});", _currentClassName, symbol.Name);
}
}
//If it's an array, dereference it using []. We need a scratch
//location because issuing two __POP() calls in the same statement
//does not guarantee left-to-right evaluation.
if (withArrayIndex)
{
Output.WriteLine(" __SCRATCH1 = __POP();");
Output.WriteLine(" __PUSH( ((__WORD*)__SCRATCH1)[ __POP() ] );");
}
}