pngunpack.f

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      subroutine pngunpack(cpack,len,idrstmpl,ndpts,fld)
 
      character(len=1),intent(in) :: cpack(len)
      integer,intent(in) :: ndpts,len
      integer,intent(in) :: idrstmpl(*)
      real,intent(out) :: fld(ndpts)
 
      integer :: ifld(ndpts)
      character(len=1),allocatable :: ctemp(:)
      integer(4) :: ieee
      real :: ref,bscale,dscale
      integer :: dec_png,width,height
 
      ieee = idrstmpl(1)
      call rdieee(ieee,ref,1)
      bscale = 2.0**real(idrstmpl(2))
      dscale = 10.0**real(-idrstmpl(3))
      nbits = idrstmpl(4)
      itype = idrstmpl(5)
!
!  if nbits equals 0, we have a constant field where the reference value
!  is the data value at each gridpoint
!
      if (nbits.ne.0) then
         allocate(ctemp(ndpts*4))
         iret=dec_png(cpack,width,height,ctemp)
         call g2_gbytesc(ctemp,ifld,0,nbits,0,ndpts)
         deallocate(ctemp)
         do j=1,ndpts
           fld(j)=((real(ifld(j))*bscale)+ref)*dscale
         enddo
      else
         do j=1,ndpts
           fld(j)=ref
         enddo
      endif
 
 
      return
      end