0     1
         +--------+--------+
         |00000010|00001000|
         +--------+--------+
          ^        ^
          |        |
          |        + less significant byte = 8
          + more significant byte = 2 x 256

   2.2. Data format

      A zlib stream has the following structure:

           0   1
         +---+---+
         |CMF|FLG|   (more-->)
         +---+---+









 
RFC 1950       ZLIB Compressed Data Format Specification        May 1996


      (if FLG.FDICT set)

           0   1   2   3
         +---+---+---+---+
         |     DICTID    |   (more-->)
         +---+---+---+---+

         +=====================+---+---+---+---+
         |...compressed data...|    ADLER32    |
         +=====================+---+---+---+---+

      Any data which may appear after ADLER32 are not part of the zlib
      stream.

      CMF (Compression Method and flags)
         This byte is divided into a 4-bit compression method and a 4-
         bit information field depending on the compression method.

            bits 0 to 3  CM     Compression method
            bits 4 to 7  CINFO  Compression info

      CM (Compression method)
         This identifies the compression method used in the file. CM = 8
         denotes the "deflate" compression method with a window size up
         to 32K.  This is the method used by gzip and PNG (see
         references [1] and [2] in Chapter 3, below, for the reference
         documents).  CM = 15 is reserved.  It might be used in a future
         version of this specification to indicate the presence of an
         extra field before the compressed data.

      CINFO (Compression info)
         For CM = 8, CINFO is the base-2 logarithm of the LZ77 window
         size, minus eight (CINFO=7 indicates a 32K window size). Values
         of CINFO above 7 are not allowed in this version of the
         specification.  CINFO is not defined in this specification for
         CM not equal to 8.

      FLG (FLaGs)
         This flag byte is divided as follows:

            bits 0 to 4  FCHECK  (check bits for CMF and FLG)
            bit  5       FDICT   (preset dictionary)
            bits 6 to 7  FLEVEL  (compression level)

         The FCHECK value must be such that CMF and FLG, when viewed as
         a 16-bit unsigned integer stored in MSB order (CMF*256 + FLG),
         is a multiple of 31.





 
RFC 1950       ZLIB Compressed Data Format Specification        May 1996


      FDICT (Preset dictionary)
         If FDICT is set, a DICT dictionary identifier is present
         immediately after the FLG byte. The dictionary is a sequence of
         bytes which are initially fed to the compressor without
         producing any compressed output. DICT is the Adler-32 checksum
         of this sequence of bytes (see the definition of ADLER32
         below).  The decompressor can use this identifier to determine
         which dictionary has been used by the compressor.

      FLEVEL (Compression level)
         These flags are available for use by specific compression
         methods.  The "deflate" method (CM = 8) sets these flags as
         follows: