source: trunk/ToBeReviewed/LECTURE/GRIB/scan_grib_recstart.pro @ 67

FUNCTION scan_grib_recstart, num

  infofile = fstat(num)
; minimum size of one record
  minisize = 8L+28L+4L+4L
  maxoffset = infofile.size-minisize
;
  start = 0L
  offset = 0L
  previousrecsize = 0L

  WHILE offset LT maxoffset DO BEGIN
; Every record must begin with 'GRIB'.
; However, their is no rule to define the space between 2 records.
; (1) we try space = previousrecsize MOD 8, because for echam outputs,
; the total size of the records is rounded to modulo 8
    addoff = 8 - (previousrecsize MOD 8)
    offset = offset+addoff
    IF offset GE maxoffset THEN GOTO, out
    a = assoc(num, bytarr(4, /nozero), offset)
    typefile = string(a[0])
    IF typefile NE 'GRIB' THEN offset = offset-addoff
; (2) we try space = previousrecsize MOD 120, because for ecmwf
; outputs, the total size of the records is rounded to modulo 120
    addoff = 120 - (previousrecsize MOD 120)
    IF typefile NE 'GRIB' THEN BEGIN
      offset = offset+addoff
      IF offset GE maxoffset THEN GOTO, out
      a = assoc(num, bytarr(4, /nozero), offset)
      typefile = string(a[0])
      IF typefile NE 'GRIB' THEN offset = offset-addoff
    ENDIF
; (3) we try space = 0
    IF typefile NE 'GRIB' THEN BEGIN
      a = assoc(num, bytarr(4, /nozero), offset)
      typefile = string(a[0])
    ENDIF
; (4) we try any value for space
    IF typefile NE 'GRIB' THEN BEGIN
      REPEAT BEGIN
        CASE 1 OF
          array_equal((a[0])[3  ], byte('G'  )):offset = offset+3
          array_equal((a[0])[2:3], byte('GR' )):offset = offset+2
          array_equal((a[0])[1:3], byte('GRI')):offset = offset+1
          else:offset = offset+4
        ENDCASE
        IF offset GE maxoffset THEN GOTO, out
        a = assoc(num, bytarr(4, /nozero), offset)
        typefile = string(a[0])
      ENDREP UNTIL typefile EQ 'GRIB'
    ENDIF
;
    start = [start, offset]
;    
    a = assoc(num, bytarr(1, /nozero), offset+4)
    recsize = bit2int([binary(a[0]), binary(a[1]), binary(a[2])])
    offset = offset+recsize
    previousrecsize = recsize
;
  ENDWHILE
;
out:
;
  RETURN, start[1:n_elements(start)-1] 
END