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 ...
for use in
PSK31. It supports all
ASCII
ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...
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 prefixing 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 sequence is a Integer sequence, sequence in which each element is the sum of the two elements that precede it. Numbers that are part of the Fibonacci sequence are known as Fibonacci numbers, commonly denoted . Many w ...
''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
Data compression