Character Pointer Operations

This procedure checks if operation is PChar ± Integer or PChar ± PChar. If so it generates code and returns True otherwise it returns False.
  Function CharacterPointerOperations: Boolean;

    Function IsOperation_PChar_Integer (Var LeftExpression, RightExpression: TExpression): Boolean;
    begin
      IsOperation_PChar_Integer := False;
      If LeftExpression.TypeDefPtr <> Ptr (SystemUnitSegment, PChar_TypeOffset) then Exit;
      IsOperation_PChar_Integer := RightExpression.TypeDefPtr^.BaseType = btInteger;
    end;

    Procedure CharacterPointerOperation;
    begin
      CharacterPointerOperations := True;
      If (RightExpression.Location = elConstant) and ((LeftExpression.Location = elConstant) or
         (LeftExpression.Location = elPointerToMemory) and not (efSegment in LeftExpression.LocationData.Flags)) then
           begin
             Case Operation of
               Calc_Add: Inc (LeftExpression.Value.Word, RightExpression.Value.Word);
               Calc_Subtract: Dec (LeftExpression.Value.Word, RightExpression.Value.Word);
             end;
             Exit;
           end;
      LeftExpression.LoadPointerToMemoryTo_DX_AX;
      RightExpression.LoadPointerToMemoryTo_DX_AX;
      RightExpression.ExtendInteger ([it16Bit, itUnsigned]);
      LoadBothExpressionsToRegisters (LeftExpression, RightExpression, [urDX, urAX]);
      Case Operation of
        Calc_Add: RightExpression.GenerateArithmeticInstructionWith_ACC (mod_ADD_rm);
        Calc_Subtract: RightExpression.GenerateArithmeticInstructionWith_ACC (mod_SUB_rm);
      end;
      LeftExpression.EndIntermediateCodeSubroutine;
      LeftExpression.UsedRegisters := LeftExpression.UsedRegisters + RightExpression.UsedRegisters;
    end;

  begin
    CharacterPointerOperations := False;
    LeftExpression.CheckForConversionOfZeroBasedCharacterArrayToPChar (RightExpression.TypeDefPtr);
    RightExpression.CheckForConversionOfZeroBasedCharacterArrayToPChar (LeftExpression.TypeDefPtr);
    Case Operation of
      Calc_Subtract: If IsOperation_PChar_Integer (LeftExpression, RightExpression) then CharacterPointerOperation;
      Calc_Add: begin
                  If IsOperation_PChar_Integer (RightExpression, LeftExpression) then ExchangeLeftAndRightExpression;
                  If IsOperation_PChar_Integer (LeftExpression, RightExpression) then CharacterPointerOperation;
                end;
    end;
  end;
 
 
 
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