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Variable Length Code Separator

IP.com Disclosure Number: IPCOM000076694D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Coleman, DE: AUTHOR [+2]

Abstract

Variable-length codes are used to reduce the average number of bits per character in recorded or transmitted data. The particular variable-run length code described lends itself to simple character separation and an implementation of this separation method.

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Variable Length Code Separator

Variable-length codes are used to reduce the average number of bits per character in recorded or transmitted data. The particular variable-run length code described lends itself to simple character separation and an implementation of this separation method.

Recording N distinct characters in straight-forward binary form requires Log N binary digits of bits. If the occurrence probability of each of the character codes is known, the average number of bits required to record a stream of these characters sometimes can be reduced, thus saving storage space and transmission time. Variable-length codes are most useful in this compaction, but they usually require a sophisticated technique for separating the individual character codes. A particular variable-length code is presented which lends itself to simple character separation.

Variable-length codes may be separated by utilizing information contained within the code itself. The coding method presented here requires that each character code contain three (3) binary ones and be terminated by the third one; e.g. 010011 would be a distinct six-digit code. The bits are accepted in a serial fashion and the 1's are counted with the third 1 defining the end of that code. The following is a list of the number of character codes available with three to ten bits: # Bits # Codes

3 1

4 3

5 6

6 10

7 15

8 21

9 28

10 36.

A total of 120 characters can be represented with ten or less bits. A simple two-di...