Repeatedly Client fail

This has been happening for years to most of us.... You start up league and it spends over an hour individually scanning files called "calulating differences;." Then when you get done after way too long, it did not change anything at all. This is a giant waste of time and is quite frustrating because I know it is just a bug in the client unable to see it already has all the files it needs. Normally if it needs a file it checks all files in a matter of minutes (3-5 minutes top) and then patches. This has been going on for a long time and it would be really nice if it fixed.