function makej()
{
    case `uname` in
    Linux)
        N=`cat /proc/cpuinfo | grep processor | wc -l`
        PARALLEL=-j`expr $N + $N`
        ;;
    Darwin)
        PARALLEL=-j`sysctl -n hw.ncpu`
        ;;
    *)
        PARALLEL=-j4
        ;;
    esac

    nice make $PARALLEL $@
}

alias mj=makej