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60 lines
2.9 KiB
Plaintext
60 lines
2.9 KiB
Plaintext
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*** ARC (compressed ARChive)
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*** Document revision: 1.4
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*** Last updated: March 11, 2004
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*** Compiler/Editor: Peter Schepers
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*** Contributors/sources: Chris Smeets (source code)
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The name is likely a shortened version of "ARChive". It is a direct
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relative of SDA, as SDA's are simply self-dissolving ARC files. ARC does
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not contain the dissolving code on the front of the file. Do not confuse
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these ARC files with C64 ARKive files (made with the ARKIVE program), or
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with PC .ARC files, as they are all completely different. Below is a dump
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of the first 48 bytes of an ARC file...
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00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F ASCII
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----------------------------------------------- ----------------
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0000: 02 01 20 9D 47 01 00 01 00 50 01 41 FE 3A 21 FE ..<2E><>G.<2E>.<2E>P.A<>:!<21>
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0010: 00 01 FE 00 02 FE 03 02 A9 00 20 90 FF A9 02 A6 <20>.<2E><>.<2E>..<2E><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>.<2E>
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0020: BA A0 01 20 BA FF A9 04 A2 35 A0 02 20 BD FF A2 <20><>.<2E><><EFBFBD><EFBFBD>.<2E>5<EFBFBD>.<2E><><EFBFBD><EFBFBD>
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Byte: $00 - ARChive version
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$01 = original
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02 = extended header
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01 - Compression mode
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$00 - Stored
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01 - Packed
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02 - Squeezed
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03 - Crunched (ARC version 2 only)
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04 - Squeezed and packed (ARC version 2 only)
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05 - Crunched in 1 pass (ARC version 2 only)
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02-03 - Checksum (low/high format)
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04-06 - Original file size in bytes (low/med/high format).
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This value is not valid if the compression mode (from
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above) is 5, a one pass crunch)
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07-08 - Number of blocks compressed file takes (low/high, 254
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bytes/block)
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09 - Filetype ("P", "S", "U", "R", uppercase in ASCII,
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lowercase in PETASCII )
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0A - Filename length
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0B-0B+length - Filename (in PETASCII, no longer than 16 characters)
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0B+length+1 - Relative file record length (only for ARC version 2)
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0B+length+2 - Date (2 bytes, in MSDOS format, only in ARC vers. 2)
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The header can also have some extra fields, depending on what version the
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archive is. Version 1 archives do not have the RECORD length and DATE
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fields, meaning they cannot contain REL files. The RECORD length is only
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used when the filetype is REL.
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Immediately following the filename (for version 1 archives) is the RLE
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control byte, and then follows the LZ table and compressed data.
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Watch out for "extra" data at the end of the file, typically many $00's.
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Some files which exist have this, and it makes reading the contained file
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list more difficult.
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64COPY can unpack ARC files easily, and just hitting return on them will
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open the archive. Simply select what files you want to extract, and copy
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them out.
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