file/magdir/compress

   1
   2 #------------------------------------------------------------------------------
   3 # compress:  file(1) magic for pure-compression formats (no archives)
   4 #
   5 # compress, gzip, pack, compact, huf, squeeze, crunch, freeze, yabba, etc.
   6 #
   7 # Formats for various forms of compressed data
   8 # Formats for "compress" proper have been moved into "compress.c",
   9 # because it tries to uncompress it to figure out what's inside.
  10
  11 # standard unix compress
  12 0       string          \037\235        compress'd data
  13 >2      byte&0x80       >0              block compressed
  14 >2      byte&0x1f       x               %d bits
  15
  16 # gzip (GNU zip, not to be confused with Info-ZIP or PKWARE zip archiver)
  17 0       string          \037\213        gzip compressed data
  18 >2      byte            <8              \b, reserved method,
  19 >2      byte            8               \b, deflated,
  20 >3      byte            &0x01           ASCII,
  21 >3      byte            &0x02           continuation,
  22 >3      byte            &0x04           extra field,
  23 >3      byte            &0x08           original filename,
  24 >3      byte            &0x10           comment,
  25 >3      byte            &0x20           encrypted,
  26 >4      ledate          x               last modified: %s,
  27 >8      byte            2               max compression,
  28 >8      byte            4               max speed,
  29 >9      byte            =0x00           os: MS-DOS
  30 >9      byte            =0x01           os: Amiga
  31 >9      byte            =0x02           os: VMS
  32 >9      byte            =0x03           os: Unix
  33 >9      byte            =0x05           os: Atari
  34 >9      byte            =0x06           os: OS/2
  35 >9      byte            =0x07           os: MacOS
  36 >9      byte            =0x0A           os: Tops/20
  37 >9      byte            =0x0B           os: Win/32
  38
  39 # packed data, Huffman (minimum redundancy) codes on a byte-by-byte basis
  40 0       string          \037\036        packed data
  41 >2      belong          >1              \b, %d characters originally
  42 >2      belong          =1              \b, %d character originally
  43 #
  44 # This magic number is byte-order-independent.  XXX - Does that mean this
  45 # is big-endian, little-endian, either, or that you can't tell?
  46 # this short is valid for SunOS
  47 0       short           017437          old packed data
  48
  49 # XXX - why *two* entries for "compacted data", one of which is
  50 # byte-order independent, and one of which is byte-order dependent?
  51 #
  52 0       short           0x1fff          compacted data
  53 # This string is valid for SunOS (BE) and a matching "short" is listed
  54 # in the Ultrix (LE) magic file.
  55 0       string          \377\037        compacted data
  56 0       short           0145405         huf output
  57
  58 # Squeeze and Crunch...
  59 # These numbers were gleaned from the Unix versions of the programs to
  60 # handle these formats.  Note that I can only uncrunch, not crunch, and
  61 # I didn't have a crunched file handy, so the crunch number is untested.
  62 #                               Keith Waclena <keith@cerberus.uchicago.edu>
  63 0       leshort         0x76FF          squeezed data (CP/M, DOS)
  64 0       leshort         0x76FE          crunched data (CP/M, DOS)
  65
  66 # Freeze
  67 0       string          \037\237        frozen file 2.1
  68 0       string          \037\236        frozen file 1.0 (or gzip 0.5)
  69
  70 # SCO compress -H (LZH)
  71 0       string          \037\240        SCO compress -H (LZH) data
  72
  73 # European GSM 06.10 is a provisional standard for full-rate speech
  74 # transcoding, prI-ETS 300 036, which uses RPE/LTP (residual pulse
  75 # excitation/long term prediction) coding at 13 kbit/s.
  76 #
  77 # There's only a magic nibble (4 bits); that nibble repeats every 33
  78 # bytes.  This isn't suited for use, but maybe we can use it someday.
  79 #
  80 # This will cause very short GSM files to be declared as data and
  81 # mismatches to be declared as data too!
  82 #0      byte&0xF0       0xd0            data
  83 #>33    byte&0xF0       0xd0
  84 #>66    byte&0xF0       0xd0
  85 #>99    byte&0xF0       0xd0
  86 #>132   byte&0xF0       0xd0            GSM 06.10 compressed audio
  87
  88 # Bzip from ulmo@Q.Net
  89 0       string          BZ              bzip compressed data,
  90 >2      byte            x               format v. %c,
  91 >3      byte            x               block size indicator %c
  92