I’m tracing a bug deep in 3rd party code, where the statement

 fStringLen := Str - fToIdent;

gives a run-time error, with:

• Str is a PChar private function parameter, it is ” at this moment
  (Initially not empty but Inc(Str) executed till the end of a loop)
• fStringlen is an integer private property, value 0
• fToIdent is a PChar private property, it shows nil {%0} in the inspector window:

It’s unclear at this moment whether anything has been done to the fToIndent PChar property (it does not have a setter that I can put a breakpoint on), or if this is just the initial state after creation of its object.

There is a somewhat older 32-bit version of our software with an older version of the 3rd party software, but where that piece of code is identical. The values are the same if I run the code, but then there is no range check error.

FWIW, this is the code:

    function TdaSynHighlighterSQL.HashKey(Str: PChar): Integer;
    // called with Str = 'absolute'
    var
      FoundDoubleMinus: Boolean;

      function GetOrd: Integer;
      begin
        case Str^ of
          '_': Result := 1;
          'a'..'z': Result := 2 + Ord(Str^) - Ord('a');
          'A'..'Z': Result := 2 + Ord(Str^) - Ord('A');
          '@':
            if fDialect in [sqlMSSQL7, sqlMSSQL2K] then
              Result := 24
            else
              Result := 0;
          else Result := 0;
        end;
      end;

    begin
      Result := 0;
      while IsIdentChar(Str^) do  // Always true until Str=''
      begin
        FoundDoubleMinus := (Str^ = '-') and ((Str + 1)^ = '-');
        if FoundDoubleMinus then Break;
        Result := (2 * Result + GetOrd) and $FFFFFF;
        inc(Str);
      end;
      Result := Result and $FF; // 255
      fStringLen := Str - fToIdent;
    end;

How to best fix this?
I find it strange that this code still would not be 64-bit proof