ARC
A file format by SEA (System Enchancement Associates) that was very popular
before Phil Katz came up with the ZIP format.
Holds multiple files but no directories like ZIP
?.
There was quite a bit of controversy in the 80's (Probably the most important event in the open source debate)
Header
|
Offset
|
Count
|
Type
|
Description
|
|
0
|
1
|
wxByte
|
ID=1Ah
|
|
1
|
1
|
wxByte
|
Compression method
|
|
2
|
13
|
wxByte
|
File name (12 bytes + \0)
|
|
15
|
1
|
wxUint32
|
Compressed file size
|
|
19
|
1
|
wxUint32
|
File date in 16(32?)-bit MS-DOS format (All zero on bits 0-16 == no date)
|
|
|
|
Bits 0-4 = day of month
|
|
|
|
Bits 5-8 = month of year
|
|
|
|
Bits 9-15 = year + 1980
|
|
|
|
Bits 16-20 = second/2 (Not displayed by UNARC, # is even)
|
|
|
|
Bits 21-26 = minute
|
|
|
|
Bits 27-31 = hour (0-24)
|
|
23
|
1
|
wxUint16
|
16-bit CRC? (0x8005, 0, true)
|
|
25
|
1
|
wxUint32
|
Original file size
|
Compression Methods
# is the compression method number from offset 1.
|
#
|
Compression Name
|
Method
|
Notes
|
|
0
|
End of archive marker
|
|
|
1
|
Unpacked
|
Uncompressed
|
No Length Field, Offset 25 is File Data, ARC 1.0-Only?
|
|
2
|
Unpacked
|
Uncompressed
|
ARC 3.1
|
|
3
|
Packed
|
RLE
|
|
|
4
|
Packed & Squeezed
|
RLE + Huffman
|
Static Conanical Huffman, ARC Pre-5.20
|
|
5
|
Crunched
|
12-bit LZW
|
ARC Pre-4.0
|
|
6
|
Packed & Crunched
|
RLE + 12-bit LZW
|
ARC Pre-4.1 (PAK documentation says 4.5)
|
|
7
|
Packed & Crunched
|
RLE + 12-bit LZW
|
(Faster Hash Algorithm - Internal to SEA) - ARC 4.6
|
|
8
|
Packed & Crunched
|
RLE + 9-X*-bit LZC
|
*X = Offset 28, only 12 has ever been accepted, ARC 5.0
|
|
9
|
Squashed
|
9-13-bit LZC
|
c/o Phil Katz, PKARC
|
|
10
|
Packed & Crushed
|
RLE + 2-13-bit LZC
|
PAK only
|
|
11
|
Distilled
|
8k Dynamic Huffman
|
8k == Size of Sliding Window, Similar to ZIP's Implode, PAK 2.51 only
|
|
12-19
|
Unknown
|
Unknown
|
ARC 6.0 ?
|
|
20-29
|
Informational items
|
Original File Size (And File Name) may be ignored, ARC 6.0
|
|
30-39
|
Control items(?)
|
Unknown
|
ARC 6.0
|
|
40+
|
Reserved
|
|
Information Items
(Sub)Header
|
Offset
|
Count
|
Type
|
Description
|
|
0
|
2
|
byte
|
Length of header (includes "length" and "type"?)
|
|
2
|
1
|
byte
|
(sub)type
|
|
3
|
?
|
byte
|
data
|
Information Item Type
|
Block type
|
Subtype
|
Description
|
20
|
|
archive info
|
0
|
archive description (ASCIIZ)
|
1
|
name of creator program (ASCIIZ)
|
2
|
name of modifier program (ASCIIZ)
|
21
|
|
file info
|
0
|
file description (ASCIIZ)
|
1
|
long name (if not MS-DOS "8.3" filename)
|
2
|
extended date-time info (reserved)
|
3
|
icon (reserved)
|
4
|
file attributes (ASCIIZ)
|
|
Attributes use an uppercase letter to signify the following:
|
|
R read access
|
|
W write access
|
|
H hidden file
|
|
S system file
|
|
N network shareable
|
22
|
|
operating system info (reserved)
|
Remarks
- wxLITTLE_ENDIAN
- UNARC and other ARC compatable archivers search 64 bytes for the 1A header if it is not found.
- Except for the beginning of the file, in which case they search an extra 3 bytes to support self-extracting (SFX?) files.
- The LZC version used in arc files is the block compress version of Z? files.
- The ARC file ends with a end-of-archive mark, two wxBytes with a value of 0x1A and 0x0.
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