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1995-08-09
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13KB
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333 lines
┴╥├ ─OCS
(╨ART 2/2)
╞ILE ┴╥├HIVE ╒TILITY...........
┬Y ITSELF ┴╥├ JUST PRINTS A SUMMARY OF THE COMMAND SYNTAX FOR ┴╥├.
├REATE NEW ┴RCHIVE.............
ARC/C D:ARCFILE[.ARC] S:PATTERN S:PATTERN .....
ARC/C/S D:ARCFILE[.ARC] S:PATTERN S:PATTERN .....
ARC/C/GZZZ D:ARCFILE[.ARC] S:PATTERN S:PATTERN .....
├REATES AN ARCHIVE ON DRIVE D: NAMED ARCFILE.ARC. ┴S MANY AS EIGHT PATTERNS
MAY BE GIVEN. /S AND /G ARE OPTIONAL. ╙OME EXAMPLES ARE:
ARC/C A:SQ B:SQ.* B:USQ.*
- CREATES AN ARCHIVE NAMED SQ.ARC ON DRIVE A WHICH INCLUDES ALL FILES FROM
DRIVE B WHOSE NAMES BEGIN WITH SQ. OR USQ.
ARC/C/S A:TEST.ARC F:*
- ARCHIVE ALL FILES FROM DRIVE 10,1 TO TEST.ARC ON DRIVE 8,0 AND SUPPRESS
COMPRESSION. (STORE ONLY)
ARC/C SEQ B:*=S
- ARCHIVES ALL SEQUENTIAL FILES ON DRIVE B TO SEQ.ARC ON THE DEFAULT DRIVE.
ARC/C/GRALPH G:SECRET A:MSSG
- ARCHIVES THE FILE MSSG ON DRIVE 8,0 TO AN ARCHIVE SECRET.ARC ON DRIVE 11,0.
THE FILE IS ENCRYPTED USING THE PASSWORD RALPH
┴PPEND TO ┼XISTING ┴RCHIVE.....
ARC/A/S D:ARCHFILE[.ARC] S:PATTERN S:PATTERN ....
┼XACTLY THE SAME AS ARC/C ETC. EXCEPT THAT THE ARCHFILE IS APPENDED TO. ╔F THE
ARCFILE DOES NOT EXIST, A FILE NOT FOUND MESSAGE IS ISSUED AND THE PROGRAM
ABORTS. ╙OMETIMES THE NUMBER OF BLOCKS DISPLAYED ON A DIRECTORY LISTING DOES
NOT AGREE WITH ┴╥├ AFTER AN APPEND. ╘HIS IS A BUG IN COMMODORE ─╧╙, AND SHOULD
BE HARMLESS.
┼XTRACT ╞ILES FROM AN ┴RCHIVE..
ARC/X[/D] <[D:]ARCHFILE[.ARC]> [PATTERN1] [PATTERN2] ...
ARC/X[/GZZZ] <[D:]ARCHFILE[.ARC]> [PATTERN1] [PATTERN2] ...
╘HIS COMMAND IS USED TO EXTRACT FILES FROM AN ARCHIVE. ╔F NO PATTERNS ARE
SPECIFIED, THEN ┴╥├ WILL EXTRACT ALL FILES FROM THE ARCHIVE. ╙OME EXAMPLES:
ARC/X A:SQ
- EXTRACTS ALL FILES FROM SQ.ARC ON DRIVE 8,0 AND PUTS THEM ON THE DEFAULT
DIRECTORY.
ARC/X A:SQ *
- SAME AS THE ABOVE
ARC/X/F B:TEMP.ARC
- EXTRACTS ALL FILES FROM TEMP.ARC ON DRIVE 8,1 AND PUTS THEM ON THE DISKETTE
IN DRIVE F: (10,1)
ARC/X/GRALPH F:SECRET
- EXTRACTS THE FILES IN AN ARCHIVE WHICH HAS BEEN ENCRYPTED WITH THE PASSWORD
RALPH, AND PLACES THEM ON THE DEFAULT DIRECTORY.
ARC/E C:BOOK030386 CHAPTER1
- EXTRACTS ONLY THE FILE 'CHAPTER1' FROM THE ARCHIVE 'BOOK030386' ON DRIVE
C:
╬╧╘┼: ARC/X AND ARC/E ARE SYNONYMS
─ISPLAY ┴RCHIVE ├ONTENTS.......
ARC/L <[D:]ARCHNAME[.ARC]>
╘HIS IS USED TO GET A LISTING OF THE FILES IN AN ARCHIVE. ╘HE LISTING WILL
DISPLAY THE FILENAME, FILETYPE, UNSQUEEZED AND SQUEEZED LENGTHS (IN DISK
BLOCKS), AND THE COMPRESSION METHOD USED. ╙OME EXAMPLE:
ARC/L B:SQ
- GIVES A LISTING OF THE FILES IN THE ARCHIVE SQ.ARC ON UNIT 8,1
╘YPE ╞ILE IN AN ┴RCHIVE........
ARC/P[/GZZZ] <[D:]ARCHNAME[.ARC]> [[PATTERN1] [PATTERN2]...]
╘HIS IS USED TO PRINT THE SPECIFIED FILES IN AN ARCHIVE TO THE SCREEN. ┘OU CAN
PAUSE THE PRINTING WITH THE ╙╚╔╞╘ KEY, AND ABORT WITH ╥╒╬/╙╘╧╨
╓ERIFY ┴RCHIVE.................
ARC/V <[D:]ARCHNAME[.ARC]> [[PATTERN1] [PATTERN2]...]
╘HIS IS USED TO VERIFY THE CONTENTS OF AN ARCHIVE. ┴╥├ CALCULATES A TWO BYTE
CHECKSUM FOR EACH FILE IN AN ARCHIVE. ╫HEN YOU VERIFY AN ARCHIVE, ┴╥├
CALCULATES A NEW CHECKSUM AND COMPARES IT WITH THE CHECKSUM STORED WHEN THE
FILE WAS ARCHIVED. ╔F THEY DO NOT MATCH, AN ERROR MESSAGE IS DISPLAYED
INDICATING THAT THE ARCHIVE MAY NOT UN-COMPRESS PROPERLY. ╬OTE: IF YOU HAVE
USED A PASSWORD WHEN CREATING THE ARCHIVE YOU NEED NOT SPECIFY IT SINCE THE
ENCRYPTED BYTES ARE USED IN CALCULATING THE CHECKSUM. ┼XAMPLE:
ARC/V B:USQ.ARC - VERIFIES USQ.ARC ON UNIT 8,1
ARC/V B:USQ USQ.LB - VERIFIES ONLY THE FILE 'USQ.LB' IN THE ARCHIVE
'USQ.ARC', AND SKIPS OVER ANY OTHER FILES.
╙YSTEM ═EMORY ═AP..................
$033C-$03FF - CASSETTE BUFFER. USED BY ┴╥├
$0801-$4000 - NOT USED
$4000-$7FFF - WORKSPACE FOR ┴╥├ AND ═╧╓┼ COMMANDS ONLY.
ALL OTHER COMMANDS LEAVE THIS AREA ALONE.
$8000-$8FFF - USED IN 80 COLUMN VERSION. (╥╧═)
$9000-$97FF - NOT USED
$9800-$9FFF - 80 COLUMN SCREEN. NOT USED IN 40 COLUMN ┴╥├
$A000-$BFFF - PROGRAM AREA
$C000-$CFFF - PROGRAM AREA. (SYS 12*4096 TO ENABLE ┴╥├
AFTER A KILL)
$D000-$FFFF - NOT PRESENTLY USED BY ┴╥├
┴ ┬╔╘ OF ╘HEORY....................
╥UN-╠ENGTH ┼NCODING............ ┴LL METHODS OF DATA COMPRESSION TAKE
ADVANTAGE OF REDUNDANCY OF ONE FORM OR ANOTHER. ╥UN-LENGTH CODING IS ONE OF
THE SIMPLEST, AND OFTEN THE MOST EFFECTIVE TECHNIQUES. ╟RAPHICS FILES MAY
OFTEN CONTAIN LONG SEQUENCES OF THE SAME BYTE. ┌EROS FOR BLANK SPACE, OR 255'S
FOR FILLED IN SPACE. ╥UN-LENGTH CODING RECODES THESE LONG SEQUENCES AS
SHORTER CONTROL SEQUENCES. ╞OR EXAMPLE, A GRAPHICAL IMAGE STORED IN ╥┴═ MAY
LOOK SOMETHING LIKE THE FOLLOWING IF VIEWED WITH THE MACHINE LANGUAGE MONITOR:
.:2000 00 00 00 00 00 00 00 00
.:2008 00 00 FF FF FF FF FF 00
.:2010 00 00 00 00 00 00 00 00
.:2018 A0 0B FF FF FF FF FF FF
AND SO ON....
╘HIS COULD BE STORED ON DISK AS THE SEQUENCE:
00 00 0A 00 FF 05 00 00 09 A0 0B 00 FF 06
╘HE FIRST ZERO IS A CONTROL CHARACTER. ╫HEN THE UNSQUEEZE ROUTINE ENCOUNTERS
A ZERO IT GETS THE NEXT TWO CHARACTERS AND INTERPRETS THEM AS A CHARACTER
IDENTIFIER AND A COUNT. ╘HUS THE FIRST 3 BYTE SEQUENCE IS INTERPRETED AS 10
ZEROS, THE NEXT 3 BYTE SEQUENCE AS 5 FF'S AND SO ON. ╫HEN A CHARACTER IS NOT
REPEATED, IT IS SIMPLY CODED DIRECTLY TO THE OUTPUT FILE. (THE $A0 AT $2018
ABOVE) ┴ND SO THE ABOVE IS SQUEEZED FROM 32 BYTES DOWN TO 14.
╘HERE IS ONE SLIGHT PROBLEM WITH THIS METHOD. ╙UPPOSE YOU ARE USING A ZERO-
BYTE AS THE CONTROL CHARACTER. ╔F A SEQUENCE OF ONLY ONE ZERO IS ENCOUNTERD,
YOU CANNOT CODE IT TO THE OUTPUT FILE SINCE IT WILL BE INTERPRETED AS A
CONTROL CHARACTER. ┘OU MUST SEND A THREE BYTE CONTROL SEQUENCE TO CODE THE
SINGLE ZERO. ┴╥├ ATTEMPTS TO CIRCUMVENT THIS PROBLEM BY CHOOSING THE BYTE THAT
OCCURS LEAST OFTEN IN THE FILE AS THE CONTROL CHARACTER. ┴N EXAMPLE OF THIS
WOULD BE AS FOLLOWS:
.:0801 06 08 01 00 8F 00 0C 08
.:0809 02 00 8F 00 12 08 03 00
.:0811 8F 00 00 00 00 00 00 00
AND SO ON....
╘HIS WOULD BE STORED ON DISK AS THE SEQUENCE:
06 08 01 00 00 01 8F 00 00 01 0C 08 02 00 00 01
8F 00 00 01 12 08 03 00 00 01 8F 00 00 07 .....
╫E WENT FROM 24 BYTES TO 30! ╬OT MUCH OF A SAVINGS.
╚UFFMAN ├ODING.................
╚UFFMAN CODING IS SOMEWHAT MORE COMPLEX. ╔T TAKES ADVANTAGE OF THE FACT THAT
SOME CHARACTERS ARE USED MORE OFTEN THAN OTHERS IN MOST FILES. ╘EXT FILES
CONTAIN MANY SPACES, AND VOWELS ARE MUCH MORE ABUNDANT THAN CONSONANTS. ╘HE
╚UFFMAN ALGORITHM αCONVERTS FIXED LENGTH CODES (8 BIT CHARACTERS) INTO CODES
WHOSE LENGTH IN BITS IS INVERSELY PROPORTIONAL TO THEIR PROBABILITY OF
OCCURANCE IN THE DATA FILE. ╞OR EXAMPLE, SUPPOSE YOUR DATA FILE LOOKED
SOMETHING LIKE THIS:
ABRACADABRA
╘HE CHARACTER FREQUENCY DISTRIBUTION IS AS FOLLOWS:
TOTAL BITS TOTAL BITS
CHARACTER FREQUENCY HUFFMAN CODE
UNSQUEEZED SQUEEZED
--------- --------- ------------
---------- ----------
A 5 0 8 * 5 = 40 1 * 5 = 5
B 2 10 8 * 2 = 16 2 * 2 = 4
R 2 111 8 * 2 = 16 3 * 2 = 6
C 1 1100 8 * 1 = 8 4 * 1 = 4
D 1 1101 8 * 1 = 8 4 * 1 = 4
ALL OTHERS 0
---------- ---------- TOTALS:
88 23
╫E COULD REPRESENT THIS INFORMATION AS A BINARY TREE:
C
/
A B /---- D
/ / /