FUNCTION read_grib_is, num, offset
;
  compile_opt idl2, strictarrsubs
;

  infofile = fstat(num)

  a = assoc(num, bytarr(4, /nozero), offset)
  typefile = string(a[0])
  IF  typefile NE 'GRIB' THEN stop
  
;
  a = assoc(num, bytarr(1, /nozero), offset+4)
  sizerecord = bit2int([binary(a[0]), binary(a[1]), binary(a[2])])
;  
  a = assoc(num, bytarr(1, /nozero), offset+7)
  gribed = a[0]
  IF gribed NE 1 THEN stop
;
  RETURN, {typefile:typefile, sizerecord:sizerecord, gribed:gribed[0]}
END