        ARC file header structure

        Byte number      Value(s)        Meaning
        --------------------------------------------------------------
        0                $1A             Header Flag
        1                0-9             Compression method
        2-14             ---             Filename.
        15-18            ---             Compressed file size.
        19-20            bits            Date format
                         15-9            Year
                          8-5            Month
                          4-0            Day
        21-22            bits            Time format
                         15-11           Hours (military)
                         10-5            Minutes
                          4-0            Seconds
        23-24            ---             CRC-16
        25-28            ---             Original file size

        Compression method
        ------------------
        1    unpacked (obsolete)
        2    unpacked
        3    packed
        4    squeezed (after packing)
        5    crunched (obsolete)
        6    crunched (after packing) (obsolete)
        7    crunched (after packing, using faster hash algorithm)
        8    crunched (after packing, using dynamic LZW variations)
        9    Squashed c/o Phil Katz (no packing) (var. on crunching)

        NOTE:    LZW is Lempel-Ziv-Welch compression algorithm

LZH
---
        LZH file header structure

        Byte number      Value(s)        Meaning
        --------------------------------------------------------------
        0                ---             Header size 
        1                ---             Cksum of remaining bytes 
        2-6              ---             Method 
        7-10             ---             Compressed size 
        11-14            ---             Uncompressed size 
        15-16            ---             Time format
        17-18            ---             Date format
        19-20            ---             File attribute 
        21-22            ---             Filename/path length 
        23-XX            ---             Filename/path 
        XX+1-XX+2        ---             CRC-16 
 
        Compression method
        ------------------ 
        -lh0-   No compression used 
        -lh1-   LZW, 4K buffer, Huffman for upper 6 bits of pos 
        -lz4-   LZW, Arithmetic Encoding 
        -lz5-   LZW, Arithmetic Encoding 

ZIP
---
        ZIP file header structures

        Local File Header
        ----------------- 
        Byte number      Value(s)        Meaning
        --------------------------------------------------------------
        0-3              $04034B50       Local File Header Signature 
        4-5              ---             Version needed to extract 
        6-7              ---             General purpose bit flag 
        8-9              0-6             Compression method 
        10-11            ---             Time
        12-13            ---             Date
        14-17            ---             CRC-32 
        18-21            ---             Compressed size 
        22-25            ---             Uncompressed size 
        26-27            ---             Filename length 
        28-29            ---             Extra field length 
        30-XX            ---             path/filename 
        XX+1-YY          ---             extra field 
 
        Central Directory Structure
        --------------------------- 
        Byte number      Value(s)        Meaning
        --------------------------------------------------------------
        0-3              $02014B50       Central file header signature 
        4                ---             Version made by 
        5                ---             Host operating system 
        6                ---             Version needed to extract 
        7                ---             O/S of version needed for extraction 
        8-9              ---             General purpose bit flag 
        10-11            0-6             Compression method 
        12-13            ---             Time
        14-15            ---             Date
        16-19            ---             CRC-32 
        20-23            ---             Compressed size 
        24-27            ---             Uncompressed size 
        28-29            ---             Filename length 
        30-31            ---             Extra field length 
        32-33            ---             File comment length 
        34-35            ---             Disk number start 
        36-37            bit             Internal file attributes 
                         0               if = 1, file is apparently an ASCII 
                                         or text file 
                         0               if = 0, file apparently contains
                                         binary data 
                         1-7             unused in version 1.0. 
        38-41            ---             External file attributes, host 
                                         system dependent 
        42-45            ---             Relative offset of local header 
                                         from the start of the first disk 
                                         on which this file appears 
        46-XX            ---             Filename or path - should not 
                                         contain a drive or device letter, 
                                         or a leading slash. All slashes 
                                         should be forward slashes '/' 
        XX+1-YY          ---             extra field 
        YY+1-ZZ          ---             file comment 
 
        End of Central Directory Structure
        ----------------------------------
        Byte number      Value(s)        Meaning
        --------------------------------------------------------------
        0-3              $06064B50       End of central dir signature 
        4-5              ---             Number of this disk 
        6-7              ---             Number of disk with start central dir 
        8-9              ---             Total number of entries in central dir 
                                         on this disk 
        10-11            ---             total number entries in central dir 
        12-15            ---             Size of the central directory 
        16-19            ---             Offset of start of central directory 
                                         with respect to the starting disk 
                                         number 
        20-21            ---             zipfile comment length 
        22-XX            ---             zipfile comment 

        ZIP Values
        ---------- 
 
        Host O/S 

        Value Description                Value Description
        ----- -------------------------- ----- ------------------------ 
        0      MS-DOS and OS/2 (FAT)     5      Atari ST 
        1      Amiga                     6      OS/2 1.2 extended file sys 
        2      VMS                       7      Macintosh 
        3      *nix                      8 thru 
        4      VM/CMS                    255    unused 

        General Purpose Bit Flag

        Bit       Description
        --------- ----------------------------------------- 
        0       If set, file is encrypted 
        1       If file Imploded and this bit is set, 8K 
                sliding dictionary was used. If clear, 4K 
                sliding dictionary was used. 
        2       If file Imploded and this bit is set, 3 
                Shannon-Fano trees were used. If clear, 2 
                Shannon-Fano trees were used. 
        3-4     unused 
        5-7     used internally by ZIP 

       Note:  Bits 1 and 2 are undefined if the compression method is 
              other than type 6 (Imploding). 

       Compression Method

       Name        Method Description
       ----------- ------ -------------------------------------------- 
       Stored         0    No compression 
       Shrunk         1    LZW, 8K buffer, 9-13 bits with partial clearing 
       Reduced-1      2    Probalistic compression, lower 7 bits 
       Reduced-2      3    Probalistic compression, lower 6 bits 
       Reduced-3      4    Probalistic compression, lower 5 bits 
       Reduced-4      5    Probalistic compression, lower 4 bits 
       Imploded       6    2/3 Shanno-Fano trees, 4K/8K sliding dictionary 

ZOO
---
        ZOO file header sturtures

        Master Header
        ------------- 
        Byte number      Value(s)        Meaning
        --------------------------------------------------------------
        0-19             ---             Archive header text
        20-23            $A7DCFDC4       File signature 
        24-27            ---             pointer to 1st header 
        28-31            ---             pointer to 1st header - 1 
        32               ---             version making archive 
        33               ---             minimum version needed to extract 
 
        File Header
        ----------- 
        Byte number      Value(s)        Meaning
        --------------------------------------------------------------
        0-3              $A7DCFDC4       signature 
        4                ---             type of directory entry 
        5                0-1             Compression method 
        6-9              ---             position of next dir entry
        10-13            ---             position of header
        14-15            ---             Date
        16-17            ---             Time
        18-19            ---             CRC-16 
        20-23            ---             Uncompressed size 
        24-27            ---             Compressed size 
        28               ---             version that made this file 
        29               ---             minimum version needed to extract 
        30               0-1             1 if file deleted from archive 
        31-34            ---             pointer to comment, 0 if none 
        35-36            ---             length of comment 
        37-XX            ---             path/filename 

        Compression Method 

        NAME        DESCRIPTION 
        ----------- -------------------------------------------- 
        Stored      No compression used 
        Crunched    Packing, LZW, 4K buffer, var len (9-13 bits) 

