Crunch
From Just Solve the File Format Problem
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* The file header is described in the text file LZDEF20.DOC shipped with [http://www.classiccmp.org/cpmarchives/cpm/mirrors/oak.oakland.edu/pub/sigm/vol294/crunch20.lbr CRUNCH20.LBR]. | * The file header is described in the text file LZDEF20.DOC shipped with [http://www.classiccmp.org/cpmarchives/cpm/mirrors/oak.oakland.edu/pub/sigm/vol294/crunch20.lbr CRUNCH20.LBR]. | ||
** An extracted copy is provided [[Crunch/LZDEF20.DOC|here]]. | ** An extracted copy is provided [[Crunch/LZDEF20.DOC|here]]. | ||
| − | ** Note that the file header follows a similar/compatible structure to | + | ** Note that the file header follows a similar/compatible structure to [[CrLZH]]. |
* FIXME: is the exact compression algorithm documented anywhere? | * FIXME: is the exact compression algorithm documented anywhere? | ||
** CRUNCH20.DOC shipped in CRUNCH20.LBR says: ''It embodies all of the concepts employed in the UNIX COMPRESS / ARC512 algorithm, but is additionally enhanced by a "metastatic code reassignment" facility. This is one of several concepts I am developing as part of an effort to advance data compression techniques beyond current performance limits. I believe this is the first time this principle has been proposed or implemented.'' | ** CRUNCH20.DOC shipped in CRUNCH20.LBR says: ''It embodies all of the concepts employed in the UNIX COMPRESS / ARC512 algorithm, but is additionally enhanced by a "metastatic code reassignment" facility. This is one of several concepts I am developing as part of an effort to advance data compression techniques beyond current performance limits. I believe this is the first time this principle has been proposed or implemented.'' | ||
Revision as of 19:32, 20 September 2020
Crunch was a method of compressing single files popular on CP/M, devised by Steve Greenberg circa 1986. It superseded Squeeze and was succeeded by CrLZH, and crunched files were common in LBR archives. The underlying compression uses the LZW algorithm.Similar to Squeeze, crunched files were signified in CP/M's 8.3 filename format by replacing the middle letter of the extension with Z (.?Z?), with the extension .ZZZ used for corner cases such as a blank extension.
See also ZSQ (LZW compression), a format that seems to be related.
Contents |
Identification
Files begin with bytes 76 fe.
Specifications
- The file header is described in the text file LZDEF20.DOC shipped with CRUNCH20.LBR.
- FIXME: is the exact compression algorithm documented anywhere?
- CRUNCH20.DOC shipped in CRUNCH20.LBR says: It embodies all of the concepts employed in the UNIX COMPRESS / ARC512 algorithm, but is additionally enhanced by a "metastatic code reassignment" facility. This is one of several concepts I am developing as part of an effort to advance data compression techniques beyond current performance limits. I believe this is the first time this principle has been proposed or implemented.
- See also "Technical Abstract" by Steven Greenberg, 16 November 1986: CRUNCH.ABS
Tools
- CFX (DOS/Unix)
- lbrate by Russell Marks, c. 2001 (Unix, GPL2)
- On CP/M (or emulators):
- The canonical tools were CRUNCH and UNCR. Possibly Greenberg's last version (Feb 1988) is v2.4: CRUNCH24.LBR, CRNCH24S.LBR (source code).
- The later LT31 deals with extracting from all of Squeeze, Crunch, CrLZH and LBR formats. Widely available in CP/M archives, e.g. LT31.LBR
- The Unarchiver
Sample files
- OAK CP/M archive → .../*.?z?
- Found in many LBR files. Note that you may have to tell your LBR utility not to decompress them (e.g.
lbrate -n).
