Varicode is a

self-synchronizing code In coding theory, especially in telecommunications, a self-synchronizing code is a uniquely decodable code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a va ...

for use in

PSK31 PSK31 or "Phase Shift Keying, 31 Baud", also BPSK31 and QPSK31, is a popular computer-sound card-generated radioteletype mode, used primarily by amateur radio operators to conduct real-time keyboard-to-keyboard chat, most often using frequenci ...

. It supports all

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...

characters, but the characters used most frequently in English have shorter codes. The space between characters is indicated by a 00 sequence, an implementation of

Fibonacci coding In mathematics and computing, Fibonacci coding is a universal code which encodes positive integers into binary code words. It is one example of representations of integers based on Fibonacci numbers. Each code word ends with "11" and contains n ...

. Originally created for speeding up real-time keyboard-to-keyboard exchanges over low bandwidth links, Varicode is freely available.

Limitations

* Varicode provides somewhat weaker compression in languages other than English that use same characters as in English.

Varicode table

Control characters

Printable characters

Character lengths

Beginning with the single-bit code "1", valid varicode values may be formed by prepending a "1" or "10" to a shorter code. Thus, the number of codes of length ''n'' is equal to the

Fibonacci number In mathematics, the Fibonacci numbers, commonly denoted , form a integer sequence, sequence, the Fibonacci sequence, in which each number is the sum of the two preceding ones. The sequence commonly starts from 0 and 1, although some authors start ...

''F_n''. Varicode uses the 88 values of lengths up to 9 bits, and 40 of the 55 codes of length 10. As transmitted, the codes are two bits longer due to the trailing delimiter 00.

References

{{Compression methods Character encoding