      subroutine comunpack(cpack,len,lensec,idrsnum,idrstmpl,ndpts,
     &                     fld,ier)
!$$$  SUBPROGRAM DOCUMENTATION BLOCK
!                .      .    .                                       .
! SUBPROGRAM:    comunpack
!   PRGMMR: Gilbert          ORG: W/NP11    DATE: 2000-06-21
!
! ABSTRACT: This subroutine unpacks a data field that was packed using a
!   complex packing algorithm as defined in the GRIB2 documention,
!   using info from the GRIB2 Data Representation Template 5.2 or 5.3.
!   Supports GRIB2 complex packing templates with or without
!   spatial differences (i.e. DRTs 5.2 and 5.3).
!
! PROGRAM HISTORY LOG:
! 2000-06-21  Gilbert
! 2004-12-29  Gilbert  -  Added test ( provided by Arthur Taylor/MDL )
!                         to verify that group widths and lengths are
!                         consistent with section length.
!
! USAGE:    CALL comunpack(cpack,len,lensec,idrsnum,idrstmpl,ndpts,fld,ier)
!   INPUT ARGUMENT LIST:
!     cpack    - The packed data field (character*1 array)
!     len      - length of packed field cpack().
!     lensec   - length of section 7 (used for error checking).
!     idrsnum  - Data Representation Template number 5.N
!                Must equal 2 or 3.
!     idrstmpl - Contains the array of values for Data Representation
!                Template 5.2 or 5.3
!     ndpts    - The number of data values to unpack
!
!   OUTPUT ARGUMENT LIST:
!     fld()    - Contains the unpacked data values
!     ier      - Error return:
!                  0 = OK
!                  1 = Problem - inconsistent group lengths of widths.
!
! REMARKS: None
!
! ATTRIBUTES:
!   LANGUAGE: XL Fortran 90
!   MACHINE:  IBM SP
!
!$$$

      character(len=1),intent(in) :: cpack(len)
      integer,intent(in) :: ndpts,len
      integer,intent(in) :: idrstmpl(*)
      real,intent(out) :: fld(ndpts)

      integer,allocatable :: ifld(:),ifldmiss(:)
      integer(4) :: ieee
      integer,allocatable :: gref(:),gwidth(:),glen(:)
      real :: ref,bscale,dscale,rmiss1,rmiss2
!      real :: fldo(6045)
      integer :: totBit, totLen

      ier=0
      !print *,'IDRSTMPL: ',(idrstmpl(j),j=1,16)
      ieee = idrstmpl(1)
      call rdieee(ieee,ref,1)
      bscale = 2.0**real(idrstmpl(2))
      dscale = 10.0**real(-idrstmpl(3))
      nbitsgref = idrstmpl(4)
      itype = idrstmpl(5)
      ngroups = idrstmpl(10)
      nbitsgwidth = idrstmpl(12)
      nbitsglen = idrstmpl(16)
      if (idrsnum.eq.3) then
         nbitsd=idrstmpl(18)*8
      endif

      !   Constant field

      if (ngroups.eq.0) then
         do j=1,ndpts
           fld(j)=ref
         enddo
         return
      endif

      iofst=0
      allocate(ifld(ndpts),stat=is)
      !print *,'ALLOC ifld: ',is,ndpts
      allocate(gref(ngroups),stat=is)
      !print *,'ALLOC gref: ',is
      allocate(gwidth(ngroups),stat=is)
      !print *,'ALLOC gwidth: ',is
!
!  Get missing values, if supplied
!
      if ( idrstmpl(7).eq.1 ) then
         if (itype.eq.0) then
            call rdieee(idrstmpl(8),rmiss1,1)
         else
            rmiss1=real(idrstmpl(8))
         endif
      elseif ( idrstmpl(7).eq.2 ) then
         if (itype.eq.0) then
            call rdieee(idrstmpl(8),rmiss1,1)
            call rdieee(idrstmpl(9),rmiss2,1)
         else
            rmiss1=real(idrstmpl(8))
            rmiss2=real(idrstmpl(9))
         endif
      endif
      !print *,'RMISSs: ',rmiss1,rmiss2,ref
! 
!  Extract Spatial differencing values, if using DRS Template 5.3
!
      if (idrsnum.eq.3) then
         if (nbitsd.ne.0) then
              call gbyte(cpack,isign,iofst,1)
              iofst=iofst+1
              call gbyte(cpack,ival1,iofst,nbitsd-1)
              iofst=iofst+nbitsd-1
              if (isign.eq.1) ival1=-ival1
              if (idrstmpl(17).eq.2) then
                 call gbyte(cpack,isign,iofst,1)
                 iofst=iofst+1
                 call gbyte(cpack,ival2,iofst,nbitsd-1)
                 iofst=iofst+nbitsd-1
                 if (isign.eq.1) ival2=-ival2
              endif
              call gbyte(cpack,isign,iofst,1)
              iofst=iofst+1
              call gbyte(cpack,minsd,iofst,nbitsd-1)
              iofst=iofst+nbitsd-1
              if (isign.eq.1) minsd=-minsd
         else
              ival1=0
              ival2=0
              minsd=0
         endif
       !print *,'SDu ',ival1,ival2,minsd,nbitsd
      endif
!
!  Extract Each Group's reference value
!
      !print *,'SAG1: ',nbitsgref,ngroups,iofst
      if (nbitsgref.ne.0) then
         call gbytes(cpack,gref,iofst,nbitsgref,0,ngroups)
         itemp=nbitsgref*ngroups
         iofst=iofst+(itemp)
         if (mod(itemp,8).ne.0) iofst=iofst+(8-mod(itemp,8))
      else
         gref(1:ngroups)=0
      endif
      !write(78,*)'GREFs: ',(gref(j),j=1,ngroups)
!
!  Extract Each Group's bit width
!
      !print *,'SAG2: ',nbitsgwidth,ngroups,iofst,idrstmpl(11)
      if (nbitsgwidth.ne.0) then
         call gbytes(cpack,gwidth,iofst,nbitsgwidth,0,ngroups)
         itemp=nbitsgwidth*ngroups
         iofst=iofst+(itemp)
         if (mod(itemp,8).ne.0) iofst=iofst+(8-mod(itemp,8))
      else
         gwidth(1:ngroups)=0
      endif
      do j=1,ngroups
        gwidth(j)=gwidth(j)+idrstmpl(11)
      enddo
      !write(78,*)'GWIDTHs: ',(gwidth(j),j=1,ngroups)
!
!  Extract Each Group's length (number of values in each group)
!
      allocate(glen(ngroups),stat=is)
      !print *,'ALLOC glen: ',is
      !print *,'SAG3: ',nbitsglen,ngroups,iofst,idrstmpl(14),idrstmpl(13)
      if (nbitsglen.ne.0) then
         call gbytes(cpack,glen,iofst,nbitsglen,0,ngroups)
         itemp=nbitsglen*ngroups
         iofst=iofst+(itemp)
         if (mod(itemp,8).ne.0) iofst=iofst+(8-mod(itemp,8))
      else
         glen(1:ngroups)=0
      endif
      do j=1,ngroups
        glen(j)=(glen(j)*idrstmpl(14))+idrstmpl(13)
      enddo
      glen(ngroups)=idrstmpl(15)
      !write(78,*)'GLENs: ',(glen(j),j=1,ngroups)
      !print *,'GLENsum: ',sum(glen)
!
!  Test to see if the group widths and lengths are consistent with number of
!  values, and length of section 7.
!
      totBit = 0
      totLen = 0
      do j=1,ngroups
        totBit = totBit + (gwidth(j)*glen(j));
        totLen = totLen + glen(j);
      enddo
      if (totLen .NE. ndpts) then
        ier=1
        return
      endif
      if ( (totBit/8) .GT. lensec) then
        ier=1
        return
      endif
!
!  For each group, unpack data values
!
      if ( idrstmpl(7).eq.0 ) then        ! no missing values
         n=1
         do j=1,ngroups
         !write(78,*)'NGP ',j,gwidth(j),glen(j),gref(j)
           if (gwidth(j).ne.0) then
             call gbytes(cpack,ifld(n),iofst,gwidth(j),0,glen(j))
             do k=1,glen(j)
               ifld(n)=ifld(n)+gref(j)
               n=n+1
             enddo
           else
             ifld(n:n+glen(j)-1)=gref(j)
             n=n+glen(j)
           endif
           iofst=iofst+(gwidth(j)*glen(j))
         enddo
      elseif ( idrstmpl(7).eq.1.OR.idrstmpl(7).eq.2 ) then
         ! missing values included
         allocate(ifldmiss(ndpts))
         !ifldmiss=0
         n=1
         non=1
         do j=1,ngroups
           !print *,'SAGNGP ',j,gwidth(j),glen(j),gref(j)
           if (gwidth(j).ne.0) then
             msng1=(2**gwidth(j))-1
             msng2=msng1-1
             call gbytes(cpack,ifld(n),iofst,gwidth(j),0,glen(j))
             iofst=iofst+(gwidth(j)*glen(j))
             do k=1,glen(j)
               if (ifld(n).eq.msng1) then
                  ifldmiss(n)=1
               elseif (idrstmpl(7).eq.2.AND.ifld(n).eq.msng2) then
                  ifldmiss(n)=2
               else
                  ifldmiss(n)=0
                  ifld(non)=ifld(n)+gref(j)
                  non=non+1
               endif
               n=n+1
             enddo
           else
             msng1=(2**nbitsgref)-1
             msng2=msng1-1
             if (gref(j).eq.msng1) then
                ifldmiss(n:n+glen(j)-1)=1
                !ifld(n:n+glen(j)-1)=0
             elseif (idrstmpl(7).eq.2.AND.gref(j).eq.msng2) then
                ifldmiss(n:n+glen(j)-1)=2
                !ifld(n:n+glen(j)-1)=0
             else
                ifldmiss(n:n+glen(j)-1)=0
                ifld(non:non+glen(j)-1)=gref(j)
                non=non+glen(j)
             endif
             n=n+glen(j)
           endif
         enddo
      endif
      !write(78,*)'IFLDs: ',(ifld(j),j=1,ndpts)

      if ( allocated(gref) ) deallocate(gref)
      if ( allocated(gwidth) ) deallocate(gwidth)
      if ( allocated(glen) ) deallocate(glen)
!
!  If using spatial differences, add overall min value, and
!  sum up recursively
!
      if (idrsnum.eq.3) then         ! spatial differencing
         if (idrstmpl(17).eq.1) then      ! first order
            ifld(1)=ival1
            if ( idrstmpl(7).eq.0 ) then        ! no missing values
               itemp=ndpts
            else
               itemp=non-1
            endif
            do n=2,itemp
               ifld(n)=ifld(n)+minsd
               ifld(n)=ifld(n)+ifld(n-1)
            enddo
         elseif (idrstmpl(17).eq.2) then    ! second order
            ifld(1)=ival1
            ifld(2)=ival2
            if ( idrstmpl(7).eq.0 ) then        ! no missing values
               itemp=ndpts
            else
               itemp=non-1
            endif
            do n=3,itemp
               ifld(n)=ifld(n)+minsd
               ifld(n)=ifld(n)+(2*ifld(n-1))-ifld(n-2)
            enddo
         endif
      !write(78,*)'IFLDs: ',(ifld(j),j=1,ndpts)
      endif
!
!  Scale data back to original form
!
      !print *,'SAGT: ',ref,bscale,dscale
      if ( idrstmpl(7).eq.0 ) then        ! no missing values
         do n=1,ndpts
            fld(n)=((real(ifld(n))*bscale)+ref)*dscale
            !write(78,*)'SAG ',n,fld(n),ifld(n),bscale,ref,1./dscale
         enddo
      elseif ( idrstmpl(7).eq.1.OR.idrstmpl(7).eq.2 ) then
         ! missing values included
         non=1
         do n=1,ndpts
            if ( ifldmiss(n).eq.0 ) then
               fld(n)=((real(ifld(non))*bscale)+ref)*dscale
               !print *,'SAG ',n,fld(n),ifld(non),bscale,ref,dscale
               non=non+1
            elseif ( ifldmiss(n).eq.1 ) then
               fld(n)=rmiss1
            elseif ( ifldmiss(n).eq.2 ) then
               fld(n)=rmiss2
            endif
         enddo
         if ( allocated(ifldmiss) ) deallocate(ifldmiss)
      endif

      if ( allocated(ifld) ) deallocate(ifld)

      !open(10,form='unformatted',recl=24180,access='direct') 
      !read(10,rec=1) (fldo(k),k=1,6045)
      !do i =1,6045
      !  print *,i,fldo(i),fld(i),fldo(i)-fld(i)
      !enddo

      return
      end
