rem: to_hour (int hours, int meridian)
add: to_hour (long int hours, int meridian)
context: to_hour (int hours, int meridian){  switch (meridian)    {    case MER24:      return 0 <= hours && hours < 24 ? hours : -1;    case MERam:      return 0 < hours && hours < 12 ? hours : hours == 12 ? 0 : -1;    case MERpm:      return 0 < hours && hours < 12 ? hours + 12 : hours == 12 ? 12 : -1;    default:      abort ();    }  /* NOTREACHED */}