得到CPU利用率的算法

    #include
    #include
    #include
    #include

    static int timer;

    void cb_quit()
    {
    gtk_timeout_remove (timer);
    gtk_main_quit();
    }

    float
    cal_load (void)
    {
    FILE * fp;
    static long pre_user, pre_nice, pre_system, pre_idle; //in order to extend easily later, i defined four vars separately
    long user, nice, system, idle;
    long d_user, d_nice, d_system, d_idle;
    static long total;
    float scale;
    char buf[1024];

    if ((fp = fopen ("/proc/stat", "r")) != NULL){
    while (fgets (buf, sizeof(buf), fp)){
    if( *buf == 'c' && *(buf+1) == 'p') break;
    }
    fclose (fp);
    }
    else
    return 0.0;

    sscanf(buf, "cpu %ld %ld %ld %ld", &user, &nice, &system, &idle);

    // calculate delta value
    d_user = user - pre_user;
    d_nice = nice - pre_nice;
    d_system = system - pre_system;
    d_idle = idle - pre_idle;

    total = d_user + d_nice + d_system + d_idle;
    if (total < 1) total = 1;
    scale = 1.0 / total;

    pre_user = user;
    pre_nice = nice;
    pre_system = system;
    pre_idle = idle;

    return (d_user + d_nice + d_system) * scale;
    }

    gint Repaint (gpointer da)
    {
    GtkWidget * drawing_area = (GtkWidget *)da;
    GdkDrawable * drawable = drawing_area->window;

    GdkGC *gc_chart, *gc_text;
    GdkColor color;

    static unsigned coory[201];
    int da_width, da_height;
    int x;
    float load;
    char buf[30];

    // set chart green
    gc_chart = gdk_gc_new (drawing_area->window);
    color.red = 0;
    color.green = 0xffff;
    color.blue = 0;
    gdk_gc_set_rgb_fg_color(gc_chart, &color );
    // set text red
    gc_text = gdk_gc_new (drawing_area->window);
    color.red = 0xffff;
    color.green = 0;
    color.blue = 0;
    gdk_gc_set_rgb_fg_color(gc_text, &color );