Prefix code: Difference between revisions

Revision as of 20:32, 6 May 2006

Revision as of 23:48, 6 May 2006

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{{cleanup-date|November 2005}}

== Introduction ==

A '''prefix code''' is a [[code]] which meets the "prefix property", which is that no code word is a [[Prefixprefix (linguisticscomputer science)|prefix]] of any other code word in the set. A code which uses code words {0,10,11} meets the prefix property; a code whose set is {0,1,10,11} does not because "1" is a prefix of both "10" and "11".

Prefix codes are also known as '''prefix-free codes''', '''comma-free codes''' or '''instantaneous codes'''; even though [[Huffman coding]] is only one algorithm for deriving prefix codes, prefix codes are also widely referred to as "Huffman codes" (even, confusingly, when the codes were not produced by a Huffman algorithm.)

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Examples of prefix codes are the variable-length [[Huffman coding|Huffman codes]], [[country calling codes]], [[ISBN]]s and the Secondary Synchronization Codes used in the [[UMTS]] [[W-CDMA]] 3G Wireless Standard.

''This article is partly derived from [[Federal Standard 1037C]], which uses the term '''comma-free code'''.''

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'''prefix codes''' are a form of [[entropy encoding]] used in [[lossless data compression]].