Crunch
From Just Solve the File Format Problem
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| + | :''This article is about the CP/M compressed file format. See the [[#Disambiguation|disambiguation section]] for other "Crunch" formats.'' | ||
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[[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 It superseded [[Squeeze]] and was succeeded by [[CrLZH]], and crunched files were common in [[LBR]] archives.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. | [[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 It superseded [[Squeeze]] and was succeeded by [[CrLZH]], and crunched files were common in [[LBR]] archives.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. | 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)]] | + | == Disambiguation == |
| + | Not to be confused with: | ||
| + | * The "crunched" compression methods used in [[ARC (compression format)|ARC]] format. These methods are possibly related to those used by CP/M Crunch, but the file formats are not otherwise similar. | ||
| + | * [[Crunch-Mania]] - An Amiga file compression utility | ||
| + | * [[Cruncher]] - An executable compression utility for DOS, by Ori Berger [http://cd.textfiles.com/simtel/simtel20/MSDOS/EXECOMP/CRUNCH10.ZIP] | ||
| + | * CRUNCH - A compression optimization utility for DOS, by Bruce Gavin. It does not appear to have any native file formats. [http://cd.textfiles.com/20mnn/ARCHIVE/CRUNCH10.ZIP] | ||
| + | * Crunch - An old [[ARC (compression format)|ARC]] compression utility by Richard P. Byrne [http://cd.textfiles.com/rbbsv3n1/d86v/crunch.zip] | ||
| + | * CRUNCH - A PKARC automation utility by Chuck Zulker [http://cd.textfiles.com/megarom/megarom1/ARC_LBR/CRUNCH.ZIP] | ||
| + | |||
| + | == See also == | ||
| + | * [[Squeeze]] - predecessor | ||
| + | * [[CrLZH]] - successor | ||
| + | * [[LBR]] - container | ||
| + | * [[ZSQ (LZW compression)]] - Possibly related | ||
== Identification == | == Identification == | ||
Revision as of 16:07, 21 September 2020
- This article is about the CP/M compressed file format. See the disambiguation section for other "Crunch" formats.
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.
Contents |
Disambiguation
Not to be confused with:
- The "crunched" compression methods used in ARC format. These methods are possibly related to those used by CP/M Crunch, but the file formats are not otherwise similar.
- Crunch-Mania - An Amiga file compression utility
- Cruncher - An executable compression utility for DOS, by Ori Berger [1]
- CRUNCH - A compression optimization utility for DOS, by Bruce Gavin. It does not appear to have any native file formats. [2]
- Crunch - An old ARC compression utility by Richard P. Byrne [3]
- CRUNCH - A PKARC automation utility by Chuck Zulker [4]
See also
- Squeeze - predecessor
- CrLZH - successor
- LBR - container
- ZSQ (LZW compression) - Possibly related
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).
