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| Commit | Line | Data |
|---|---|---|
| 30b1626c C |
1 | .TH COMPACT 1 "18 January 1983" |
| 2 | .UC 4 | |
| 3 | .SH NAME | |
| 4 | compact, uncompact, ccat \- compress and uncompress files, and cat them | |
| 5 | .SH SYNOPSIS | |
| 6 | .B compact | |
| 7 | [ name ... ] | |
| 8 | .br | |
| 9 | .B uncompact | |
| 10 | [ | |
| 11 | name ... | |
| 12 | ] | |
| 13 | .br | |
| 14 | .B ccat | |
| 15 | [ file ... ] | |
| 16 | .SH DESCRIPTION | |
| 17 | .I Compact | |
| 18 | compresses the named files using an adaptive Huffman code. If no file | |
| 19 | names are given, the standard input is compacted to the standard output. | |
| 20 | .I Compact | |
| 21 | operates as an on-line algorithm. Each time a byte is read, | |
| 22 | it is encoded immediately according to the current prefix code. | |
| 23 | This code is an optimal Huffman code for the set of frequencies seen so far. | |
| 24 | It is unnecessary to prepend a decoding tree to the compressed file | |
| 25 | since the encoder and the decoder start in the same state and stay | |
| 26 | synchronized. Furthermore, | |
| 27 | .I compact | |
| 28 | and | |
| 29 | .I uncompact | |
| 30 | can operate as filters. In particular, | |
| 31 | .sp | |
| 32 | ... | compact | uncompact | ... | |
| 33 | .br | |
| 34 | .sp | |
| 35 | operates as a (very slow) no-op. | |
| 36 | .PP | |
| 37 | When an argument | |
| 38 | .I file | |
| 39 | is given, it is compacted and the resulting file is placed in | |
| 40 | .I file.C; | |
| 41 | .I file | |
| 42 | is unlinked. The first two bytes of the compacted file code the | |
| 43 | fact that the file is compacted. This code is used to prohibit recompaction. | |
| 44 | .PP | |
| 45 | The amount of compression to be expected depends on the type of file being | |
| 46 | compressed. Typical values of compression are: | |
| 47 | Text (38%), Pascal Source (43%), C Source (36%) and Binary (19%). | |
| 48 | These values are the percentages of file bytes reduced. | |
| 49 | .PP | |
| 50 | .I Uncompact | |
| 51 | restores the original file from a file compressed by | |
| 52 | .I compact. | |
| 53 | If no file names are given, the standard input is uncompacted to | |
| 54 | the standard output. | |
| 55 | .PP | |
| 56 | .I Ccat | |
| 57 | cats the original file from a file compressed by | |
| 58 | .I compact, | |
| 59 | without uncompressing the file. | |
| 60 | .SH RESTRICTION | |
| 61 | The last segment of the filename must contain fewer than thirteen characters | |
| 62 | to allow space for the appended '.C'. | |
| 63 | .SH FILES | |
| 64 | .ta 1i | |
| 65 | *.C compacted file created by compact, removed by uncompact | |
| 66 | .SH "SEE ALSO" | |
| 67 | Gallager, Robert G., `Variations on a Theme of Huffman', | |
| 68 | .I "I.E.E.E. Transactions on Information Theory," | |
| 69 | vol. IT-24, no. 6, November 1978, pp. 668 - 674. | |
| 70 | .SH AUTHOR | |
| 71 | Colin L. Mc Master |