/* Subrogram:  invtime.c
       Author:  Mylene J. Remigio
         Date:  November 12, 1997

    Revision:  For Y2K
      Author:  Shyam Lakshmin
        Date:  July 8, 1999

    This procedure converts the minute timestamp for WOCE-MET ship
    data back into a standard year/month/day/hour/minute time. 
    Based on the subroutine invtime.f
    
    INPUT VALUE: 
    
    timestamp integer Number (in minutes) which repersents the
                                time after January 1, 1980, at 00:00
                                UTC.  Range is [0,21565439]
                                
    
    OUTPUT VALUES: 
       
    **NOTE:  yr, mon, day, hr, and min are passed in the calling, but
             they are set to zero once the subprogram is initialized. **

    yr integer Year from timestamp.  Range is
                                [1980, 2020] If the year is greater
                                than 1999, year is set to -9999 and 0
                                is the value of mon, day, hr, and min. 
    mon integer The month from timestamp.  Range is
                                [1,12]
    day integer The day from timestamp.  Range is
                                [1,31], depending on the month
    hr integer The hour from timestamp.  Range is
                                [0,23]
    min integer The minute from timestamp.  Range is
                                [0,59]
                                                                
***********************************************************************/

void invtime(int timestamp, int *yr, int *mon, int *day, int *hr, int
*min) 
  {
   int year[42] = {0, 527040, 1052640, 1578240, 2103840, 2630880,
       3156480, 3682080, 4207680, 4734720, 5260320, 5785920, 6311520,
       6838560, 7364160, 7889760, 8415360, 8942400, 9468000, 9993600,
       10519200, 11046240, 11571840, 12097440, 12623040, 13150080,
       13675680, 14201280, 14726880, 15253920, 15779520, 16305120,
       16830720, 17357760, 17883360, 18408960, 18934560, 19461600,
       19987200, 20512800, 21038400, 21565440}; 
   int month[13] = {0, 44640, 84960, 129600, 172800, 217440, 260640,
       305280, 349920, 393120, 437760, 480960, 525600}; 
   int leap_mon[13] = {0, 44640, 86400, 131040, 174240, 218880, 262080,
       306720, 351360, 394560, 439200, 482400, 527040}; 
   int min_day = 1440; 
   int min_hr = 60; 
   int iyr, imon, iday, ihour, itime, ttime, i; 
/* YEAR CALCULATION */

 
   if (timestamp >= year[41]) 
     {
      *yr = -9999; 
      return; 
     }

   iyr = 1979; 
   itime = timestamp; 

   for (i = 0; i < 41; i++) 
     {
      iyr = iyr++; 
      ttime = itime - year[i + 1]; 
      if (ttime < 0) 
        {
         itime = itime - year[i]; 
         break; 
        }
     }
     
/* Year has been calculated -- assign return value.  */

   *yr = iyr; 
   
/* MONTH CALCULATION */

   imon = 0; 
             
/* calculation of month for leap years */

   if (iyr%4 == 0) 
     {
      for (i = 0; i < 12; i++) 
        {
         imon = imon++; 
         ttime = itime - leap_mon[i + 1]; 
         if (ttime < 0) 
           {
            itime = itime - leap_mon[i]; 
            break; 
           }
        }
     }

/* calculation of month for non-leap years */

   else
     {
      for (i = 0; i < 12; i++) 
        {
         imon = imon++; 
         ttime = itime - month[i + 1]; 
         if (ttime < 0) 
           {
            itime = itime - month[i]; 
            break; 
           }
        }
     }

/* Return month value.  */
     
   *mon = imon; 

/* DAY CALCULATION */
   
   iday = 0; 
   
   for (i = 0; i < 31; i++) 
     {
      iday = iday++; 
      ttime = itime - ( min_day * (i + 1) ); 
      if (ttime < 0) 
        {
         itime = itime - ( min_day * i ); 
         break; 
        }
     }

/* Return day calculation.  */
   
      *day = iday; 
           
/* HOUR CALCULATION. */

   ihour = -1; 
   
   for (i = 0; i < 24; i++) 
     {
      ihour = ihour++; 
      ttime = itime - ( min_hr * (i + 1) ); 
      if (ttime < 0) 
        {
         itime = itime - ( min_hr * i ); 
         break; 
        }
     }
     
   *hr = ihour; 
      
/* MINUTE CALCULATION. */
   
   *min = itime; 

  }