Reapply coordinate fix patch

    commit e452707b3db9b0a3ae33c792f46e5350ba63a4b5
    Author: Kenji Rikitake <kenji.rikitake@acm.org>
    Date:   Tue Feb 18 09:33:55 2014 +0900

        Update computer.c

        * Fix quadrant coordinate boundary in the course calculation