I tested speed now. Simple cycle case sensitive search for substring in string 1 000 000 times takes about 2s. For 2 000 000 000 more than 1 hour. For such long run is necessary to show some progress, make application react for user + read strings from list. In the final it means about 3-4 hours of program run.
For case insensitive I see one possibility only - convert both files e.g. to uppercase before search. Convert strings inside cycle will cause several thousand times more conversion and it will significantly slow down searching. -- <http://forum.pspad.com/read.php?2,63366,63429> PSPad freeware editor http://www.pspad.com
