Notes for ARC 5.21 June 6, 1988 This program is based on the MSDOS ARC program, version 5.21, plus a few enhancements... o ARC also performs Huffman Squeezing on data. The Huffman Squeeze algorithm was removed from MSDOS ARC after version 5.12. It turns out to be more efficient than Lempel-Ziv style compression when compressing graphic images. Squeeze analysis is always done now, and the best of packing, squeezing, or crunching is used. o Compresses and extracts Squashed files. "Squashing" was created by Phil Katz in his PKxxx series of ARC utility programs for MSDOS. Dan Lanciani wrote the original modifications to ARC's Crunch code to handle Squashing. I've made minor changes since then, mostly to reduce the amount of memory required. The 'q' option flag must be specified to Squash files. The Squashing algorithm will be used instead of the usual Crunch algorithm, and will be compared against packing and squeezing, as before. System specific notes: On MTS, an additional option flag, 'i' for "image mode," was used. ARC assumes files are text, by default, and will translate MTS files from EBCDIC to ASCII before storing in an archive, and translates from ASCII to EBCDIC upon extraction. Specifying the 'i' flag will inhibit this translation. This would most commonly be used when shipping binary images such as TeX DVI files, other .ARC files stored within an archive, etc... The 'r' (run) command is omitted. It just doesn't seem very useful. Also, ARC cannot restore MTS files with their original time stamps. (Maybe in a future release...) On Unix(tm) systems, the 'i' flag is also present. Unix ARC assumes a binary file, by default. Here the only translation involved is in end-of-line processing. When storing text files, ARC will change '\n' to '\r\n', and does the opposite when extracting files. Carriage returns in any other location are preserved when extracting. This translation only occurs if the 'i' flag is given. On the Atari ST, the 'h' (for "hold screen") option is present, which simply delays exiting the program. This is typically used when executing ARC from the desktop, to allow reading all of ARC's output before the screen is cleared and the desktop is redrawn. The program will prompt and wait for a keypress before exiting. Note that since there are no "options" for the MARC program, the "hold screen" option is always active for MARC. On both Unix and Atari systems, ARC & MARC will search for an environment variable named "ARCTEMP" or "TMPDIR." If present, any temporary files will be created in the specified directory. This is probably insignificant for Unix users, but can be handy on the Atari, in combination with a RAMdisk. Highly recommended for floppy users. (Unfortunately, you can only take advantage of this when running some form of command shell that allows setting environment variables. Thus, you won't see any speed gains when running from the desktop.) That about covers things. The enclosed documentation is taken directly from the MSDOS distribution of ARC. Unless specified differently here, the programs behave indentically. Note that ARC521.DOC is identical to ARC520.DOC - the differences between the two versions are described in the file CHANGES.521. Oh yeah - this program may be distributed freely so long as you don't modify it in any way. You may not charge for distributing it. (Don't feel bad, I can't charge for it either. }-) It'd be nice if you kept this and the other enclosed doc files with it when distributing, but I'm not going to make a fuss about it. Most people are so familiar with the program by now that it wouldn't matter much anyway. You should keep this README file around, so bug reports & such will find their way back to me. (Bugs? What bugs? Nah, there aren't any bugs...) / Howard Chu ___ /_ , ,_. University of Michigan / /(_/(__ hyc@umix.cc.umich.edu / umix!hyc '
