pngunpack.F90

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subroutine pngunpack(cpack, len, idrstmpl, ndpts, fld)
  implicit none
  
  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 :: width, height
  integer :: iret, itype, j, nbits
 
  interface
     function dec_png(pngbuf, width, height, cout) bind(c, name="dec_png")
       use iso_c_binding
       character(kind = c_char), intent(in) :: pngbuf(*)
       integer(c_int), intent(in) :: width, height
       character(kind = c_char), intent(out) :: cout(*)
       integer(c_int) :: dec_png
     end function dec_png
  end interface
 
  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
end subroutine pngunpack