subroutine addsec(idate,nvalues,incsec,ldate)

c    subroutine to add or subtract a time increment (input in seconds) to
c         a date. nvalues indicates whether idate is a 5 or 6 value input
c         date.
c
c
c
c	Y2K checked.  Works with either 2 or 4 digit years.
c
c   for nvalues = 5
C 
C     idate(1)     = hour
C     idate(2)     = minute
C     idate(3)     = day
C     idate(4)     = month
C     idate(5)     = year
C     idate(6)     = seconds set to 0
c
c   for nvalues = 6
C 
C     idate(1)     = hour
C     idate(2)     = minute
C     idate(3)     = sec
C     idate(4)     = day
C     idate(5)     = month
C     idate(6)     = year
c
c   for nvalues = 6 the values are remapped below to look like nvalues=5
c
c
C 
      DIMENSION nday(12),idate(6),ldate(6)
      DATA nday/31,28,31,30,31,30,31,31,30,31,30,31/
C 
C     ADJUST FOR LEAP YEAR. 
C 
      nday(2)=28
      if (MOD(idate(5),4).EQ.0) nday(2)=29


	if (nvalues.eq.5) then
	   idate(6) = 0
	elseif (nvalues.eq.6) then
	    iy = idate(6)
	    idate(6) = idate(3)
	    idate(3) = idate(4)
	    idate(4) = idate(5)
	    idate(5) = iy
	else
	    write(6,'(a)') 
     1       '  Error - number of values in date must be 5 or 6'
	endif


c  convert 2 digit year to 4 digit year, convert back if iyrdigit.ne.4
c     only works for 1950 to 2050 
c	if (idate(5).ge.50.and.idate(5).lt.100) then
c              idate(5) = idate(5) + 1900
c	elseif (idate(5).lt.50) then
c              idate(5) = idate(5) + 2000
c	else
c	       iyrdigit = 4
c	endif

	nsectot = idate(6) + incsec
	   if (nsectot.lt.0) then
	       nminsub = nsectot/60 -1
	       nsectot = nsectot - nminsub*60
	       if (nsectot.eq.60) then 
		nsectot = 0
		nminsub = nminsub + 1
	       endif
	       nmintot = idate(2) + nminsub
	   else
	       nminadd = nsectot/60
	       nsectot = nsectot - nminadd*60
	       nmintot = idate(2) + nminadd
	   endif
	   if (nmintot.lt.0) then
	       nhrsub = nmintot/60 - 1
	       nmintot = nmintot - nhrsub*60
	       if (nmintot.eq.60) then 
		nmintot = 0
		nhrsub = nhrsub + 1
	       endif
	       nhrtot = idate(1) + nhrsub
	   else
	       nhradd = nmintot/60
	       nmintot = nmintot - nhradd*60
	       nhrtot = idate(1) + nhradd
	   endif
	   if (nhrtot.lt.0) then
	       ndaysub = nhrtot/24 - 1
	       nhrtot = nhrtot - ndaysub*24
	       if (nhrtot.eq.24) then 
		nhrtot = 0
		ndaysub = ndaysub + 1
	       endif
	       ndaytot = idate(3) + ndaysub
	   else
	       ndayadd = nhrtot/24
	       nhrtot = nhrtot - ndayadd*24
	       ndaytot = idate(3) + ndayadd
	   endif

920    iy=idate(5) 
      nmon=idate(4)
      nd=ndaytot 

	if(nd.le.0) then
	nday(2)=28
	if(mod(iy,4).eq.0) nday(2)=29
	 if(nmon.eq.1) then
	 nmon=12
	 iy=iy-1
	 nd=31+nd
	 else
	 nmon=nmon-1
	 nd=nday(nmon)+nd
	 endif
	go to 940
	endif

	if (MOD(iy,4).eq.0) nday(2)=29

960     if (nd.le.nday(nmon)) go to 940 
930     nd=nd-nday(nmon) 
        nmon=nmon+1 
	if (nmon.le.12) go to 960       
	iy=iy+1 
	nday(2)=28
	if (MOD(iy,4).eq.0) nday(2)=29
	nmon=1 
	if (iy.ge.100.and.idate(5).lt.100) iy=0
	go to 960 

940     if (iy.lt.0) iy = 100 + iy
	if (nvalues.eq.5) then	  
	  ldate(1) = nhrtot
	  ldate(2) = nmintot
	  ldate(3) = nd
	  ldate(4) = nmon
	  ldate(5) = iy
	  ldate(6) = nsectot
	elseif (nvalues.eq.6) then
	  ldate(1) = nhrtot
	  ldate(2) = nmintot
	  ldate(3) = nsectot
	  ldate(4) = nd
	  ldate(5) = nmon
	  ldate(6) = iy
	else
	    write(6,'(a)') 
     1       '  Error - number of values in date must be 5 or 6'
	endif

	return
	end