Prefix code: Difference between revisions

Revision as of 04:35, 20 April 2023

Revision as of 04:40, 20 April 2023

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==Techniques==

If every Wordword in the code has the same length, the code is called a '''fixed-length code''', or a '''block code''' (though the term [[block code]] is also used for fixed-size [[error-correcting code]]s in [[channel coding]]). For example, [[ISO 8859-15]] letters are always 8 bits long. [[UTF-32/UCS-4]] letters are always 32 bits long. [[Asynchronous Transfer Mode|ATM cells]] are always 424 bits (53 bytes) long. A fixed-length code of fixed length ''k'' bits can encode up to <math>2^{k}</math> source symbols.

A fixed-length code is necessarily a prefix code. It is possible to turn any code into a fixed-length code by padding fixed symbols to the shorter prefixes in order to meet the length of the longest prefixes. Alternately, such padding codes may be employed to introduce redundancy that allows autocorrection and/or synchronisation. However, fixed length encodings are inefficient in situations where some words are much more likely to be transmitted than others.