/**
 *******************************************************************************
 *  \brief Return day of week based on day, month and year (work up to 2099 year)
 *
 *  \param day(1..31), month(1..12), year (0..99 from 2000)
 *
 *  \return day of week: 1(monday)..7(sunday)
 *
 *  \note   day, month, year not checked!
 *
 ******************************************************************************/
static const char mmmArray[12]={0,3,3,6,1,4,6,2,5,0,3,5}; // вынесена из локальных переменных на всякий случай!

static char GetWeekDay(char day, char month, char year)
{
    return (mmmArray[month-1]
            + day
            + year
            + (year/4)
            -((month<3&&year%4==0)?1:0)+5)%7
            +1;
}