//See ::/Doc/TimeDate.DD

U16 mon_start_days1[12]=
{
  0,31,59,90,120,151,181,212,243,273,304,334
};
U16 mon_start_days2[12]=
{
  0,31,60,91,121,152,182,213,244,274,305,335
};

I64 YearStartDate(I64 year)
{//32-bit day since AD 0, given year number.
  I64 y1=year-1,yd4000=y1/4000,yd400=y1/400,yd100=y1/100,yd4=y1/4;
  return year*365+yd4-yd100+yd400-yd4000;
}

CDate Struct2Date(CDateStruct *_ds)
{//Cvt CDateStruct to CDate.
  CDate cdt;
  I64 i1,i2;
  i1=YearStartDate(_ds->year);
  i2=YearStartDate(_ds->year+1);
  if (i2-i1==365)
    i1+=mon_start_days1[_ds->mon-1];
  else
    i1+=mon_start_days2[_ds->mon-1];
  cdt.date=i1+_ds->day_of_mon-1;
  cdt.time=(_ds->sec10000+100*(_ds->sec100+100*(_ds->sec
                               +60*(_ds->min+60*_ds->hour))))<<21/(15*15*3*625);
  return cdt;
}

I64 DayOfWeek(I64 i)
{//Day of week, given 32-bit day since AD 0.
  i+=CDATE_BASE_DAY_OF_WEEK;
  if (i>=0)
    return i % 7;
  else
    return 6-(6-i)%7;
}

U0 Date2Struct(CDateStruct *_ds,CDate cdt)
{//Cvt CDate to CDateStruct.
  I64 i,k,date=cdt.date;
  _ds->day_of_week=DayOfWeek(date);
  _ds->year=(date+1)*100000/CDATE_YEAR_DAYS_INT;
  i=YearStartDate(_ds->year);
  while (i>date)
  {
    _ds->year--;
    i=YearStartDate(_ds->year);
  }
  date-=i;
  if (YearStartDate(_ds->year+1)-i==365)
  {
    k=0;
    while (date>=mon_start_days1[k+1] && k<11)
      k++;
    date-=mon_start_days1[k];
  }
  else
  {
    k=0;
    while (date>=mon_start_days2[k+1] && k<11)
      k++;
    date-=mon_start_days2[k];
  }
  _ds->mon=k+1;
  _ds->day_of_mon=date+1;
  k=(625*15*15*3*cdt.time)>>21+1;
  _ds->sec10000=ModU64(&k,100);
  _ds->sec100=ModU64(&k,100);
  _ds->sec=ModU64(&k,60);
  _ds->min=ModU64(&k,60);
  _ds->hour  =k;
}

I64 FirstDayOfMon(I64 i)
{//First day of month, given 32-bit day since AD 0.
  CDateStruct ds;
  CDate cdt=0;
  cdt.date=i;
  Date2Struct(&ds,cdt);
  ds.day_of_mon=1;
  cdt=Struct2Date(&ds);
  return cdt.date;
}

I64 LastDayOfMon(I64 i)
{//Last day of month, given 32-bit day since AD 0.
  CDateStruct ds;
  CDate cdt=0;
  cdt.date=i;
  Date2Struct(&ds,cdt);
  ds.mon++;
  if (ds.mon==13)
  {
    ds.mon=0;
    ds.year++;
  }
  ds.day_of_mon=1;
  cdt=Struct2Date(&ds);
  return cdt.date-1;
}

I64 FirstDayOfYear(I64 i)
{//First day of year, given 32-bit day since AD 0.
  CDateStruct ds;
  CDate cdt=0;
  cdt.date=i;
  Date2Struct(&ds,cdt);
  ds.day_of_mon=1;
  ds.mon=1;
  cdt=Struct2Date(&ds);
  return cdt.date;
}

I64 LastDayOfYear(I64 i)
{//Last day of year, given 32-bit day since AD 0.
  CDateStruct ds;
  CDate cdt=0;
  cdt.date=i;
  Date2Struct(&ds,cdt);
  ds.day_of_mon=1;
  ds.mon=1;
  ds.year++;
  cdt=Struct2Date(&ds);
  return cdt.date-1;
}

I64 Bcd2Bin(U64 b)
{
  I64 i,res=0;
  for (i=0; i<16; i++)
  {
    res=res*10+b>>60;
    b<<=4;
  }
  return res;
}

U0 NowDateTimeStruct(CDateStruct *_ds)
{
  I64 i;
  U8 *b=_ds;
  Bool is_bcd;
  MemSet(_ds,0,sizeof(CDateStruct));
  PUSHFD
  CLI
  while (LBts(&sys_semas[SEMA_SYS_DATE],0))
    PAUSE
    OutU8(0x70,0x0A);
  do
  {
    while (InU8(0x71) & 0x80)
      PAUSE
      OutU8(0x70,0);
    b[2]=InU8(0x71);
    OutU8(0x70,2);
    b[3]=InU8(0x71);
    OutU8(0x70,4);
    b[4]=InU8(0x71);
    OutU8(0x70,6);
    b[5]=InU8(0x71);
    OutU8(0x70,7);
    b[6]=InU8(0x71);
    OutU8(0x70,8);
    b[7]=InU8(0x71);
    OutU8(0x70,9);
    b[8]=InU8(0x71);
    OutU8(0x70,0x0A);
  }
  while (InU8(0x71) & 0x80);
  OutU8(0x70,0x0B);
  if (InU8(0x71) & 4)
    is_bcd=FALSE;
  else
    is_bcd=TRUE;
  LBtr(&sys_semas[SEMA_SYS_DATE],0);
  POPFD
  if (is_bcd)
    for (i=2; i<9; i++)
      b[i]=Bcd2Bin(b[i]);
  if (_ds->year>255)    _ds->year=255;
  _ds->year+=2000;
  if (_ds->mon>12)      _ds->mon=12;
  if (_ds->day_of_mon>31) _ds->day_of_mon=31;
  if (_ds->day_of_week>6) _ds->day_of_week=6;
  if (_ds->hour>23)     _ds->hour=23;
  if (_ds->min>59)      _ds->min=59;
  if (_ds->sec>59)      _ds->sec=59;
}

CDate Now()
{//Current datetime.
  CDateStruct ds;
  NowDateTimeStruct(&ds);
  return Struct2Date(&ds)-local_time_offset;
}