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Topic: Prefix code

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In the News (Fri 22 Jun 18)

  Prefix code - Wikipedia, the free encyclopedia
A prefix code, also known as a prefix-free code, comma-free code or instantaneous code, is a code constructed so that dividing the code word into two pieces cannot result in the first being a code word.
This property permits the proper framing of transmitted code words when (a) external synchronization is provided to identify the start of the first code word in a sequence of code words and (b) no uncorrected errors occur in the symbol stream.
prefix codes are a form of entropy encoding used in lossless data compression.
en.wikipedia.org /wiki/Prefix_code   (1138 words)

 Huffman coding - Wikipedia, the free encyclopedia
The term refers to the use of a variable-length code table for encoding a source symbol (such as a character in a file) where the variable-length code table has been derived in a particular way based on the estimated probability of occurrence for each possible value of the source symbol.
LZW coding can also often be more efficient, particularly when the input symbols are not independently-distributed, because it does not depend on encoding each input symbol one at a time (instead, it batches up a variable number of input symbols into each encoded syntax element).
Huffman coding with unequal letter costs is the generalization in which this assumption is no longer assumed true: the letters of the encoding alphabet may have non-uniform lengths, due to characteristics of the transmission medium.
en.wikipedia.org /wiki/Huffman_coding   (1559 words)

 Entropy-coding system - Patent 4939583
With this provision of a cluster code, as compared with a system in which a code type judge bit is added at the first bit position of the Huffman code and the run length code, the coding efficiency is improved and the total number of the bits after the coding operation can be reduced.
Incidentally, the Huffman code switch signal (e) and the code validity signal (f) are generated from the 0 detect signal (c) and the signal obtained by delaying the 0 detect signal (c) by one clock in the control signal generate circuit 14.
Incidentally, the code validity signal (e) is generated through an NAND operation between the 0 detect signal (c) and the signal obtained by delaying the 0 detect signal (c) by one clock in the control signal generate circuit 14.
www.freepatentsonline.com /4939583.html   (2983 words)

 List of country calling codes - Open Encyclopedia   (Site not responding. Last check: 2007-10-21)
The numbers are a prefix code so that no number has an initial segment that is an existing shorter number.
This code is used to dial into the country specified; each country also has an international call prefix used to dial out of the country.
This is similar to the use of a trunk code in countries such as the United States, which uses a leading "1" to indicate that a national area code follows, except that the trunk code has been absorbed into the area code, for presentational reasons.
open-encyclopedia.com /List_of_country_calling_codes   (641 words)

 Howstuffworks "What do digits in phone numbers mean?"
Prefix - The prefix originally referred to the specific switch that a phone line connected to.
Think of the three parts like a street address, where the area code is the city, the prefix is the street and the line number is the house.
When a new area code is needed, a decision must be made as to whether the existing area code should be split or the new area code overlaid on the existing one.
www.howstuffworks.com /question659.htm   (761 words)

 Encyclopedia: ZIP Code
ZIP Codes are numbered with the first digit representing a certain group of U.S. states, the second and third digits together representing a region in that group (or perhaps a large city), and the fourth and fifth digits representing more specific areas, such as small towns or regions of that city.
For example, ZIP codes beginning with 0 and 1 are in use in New York; beginning with 2 and 5, in the District of Columbia; and beginning with 7 and 8, in Texas.
For example, ZIP code 03750 is for Etna, NH, but Etna is not a municipality, it is actually a village district in the town of Hanover, New Hampshire (Zip Code 03755).
www.nationmaster.com /encyclopedia/ZIP-Code   (7457 words)

 Indexed-indirect addressing using prefix codes - Patent 4531200
The prefix codes and index values are merely catenated to provide multiple levels of indexed indirection, each pair of prefix codes and suffix values surrounding the instruction like a matched pair of parentheses.
The architectural cost of the invention is low because, apart from the one or two fixed code points taken from the op-code space, only the actual use of indexed indirection in a particular instance incurs the extra instruction length required by the prefix code and the index value.
When one or more prefix code bytes PR are detected in the instruction stream, their occurrences are recorded.
www.freepatentsonline.com /4531200.html   (5932 words)

 Coding   (Site not responding. Last check: 2007-10-21)
The prefix property allows us to identify the end of the first (and second etc.) code word in a data stream immediately, and is required to be able to decode a stream of data unambiguously without look-ahead.
While the prefix property seems to be quite strict, some fundamental results show that such codes are all that we need to consider for the purposes of inference.
Arithmetic coding places a limit on the accuracy required; the price is a small loss in coding efficiency and Langdon (1984) states "less than 4%" for the choices in that paper.
www.csse.monash.edu.au /~lloyd/tildeMML/Notes/Coding.html   (1553 words)

 Lecture 24: Huffman Codes
In fact, this is an optimal character code for this file (which is not to say that the file is not further compressible by other means).
Prefix codes are useful because they make a stream of bits unambiguous; we simply can accumulate bits from a stream until we have completed a codeword.
The solution is adaptive Huffman coding, which builds the prefix tree incrementally in such a way that the coding always is optimal for the sequence characters already seen.
www.cs.cornell.edu /courses/cs312/2001sp/lecture/lecture_24.htm   (1169 words)

 CIPO - Canadian Patent Database - Claims - 1223965
The compression apparatus of claim 9 in which each said location of said memory means comprises a prefix code field for storing the code signal corresponding to the prefix string of the string stored thereat, and a string code field for storing the code signal of the string stored thereat.
said control means includes means for controlling the insertion of the code signal held in said further code register means and the character signal held in said last character holding means into the prefix code field and the character field, respectively, of the location of said memory means addressed by said assigned code signal.
The decompression apparatus of claim 31 further including initializing means for storing in the prefix code fields of said locations of said memory means an empty indicia signal representing that the location storing said empty indicia signal is empty, said empty indicia signal having a value not equal to any compressed code signal.
patents1.ic.gc.ca /claims?patent_number=1223965&language=EN   (2451 words)

 CS251- Winter 1999- Practice questions   (Site not responding. Last check: 2007-10-21)
A prefix code is a collection of codewords, one per symbol, such that no codeword can be found as the prefix (leftmost part) of any other codeword.
Finally, the counterexample: if the prefix code for input symbols A and B has codewords 00 and 01, then the sequence 1111 cannot be decoded.
From the previous exercise, the average code length is 1/2 + 2/4 + 3/8 +...
cgm.cs.mcgill.ca /~luc/practice99c-answers.html   (1042 words)

 6 Mar 1996
A binary prefix code is a code in which every symbol (for example, letters of the alphabet) is assigned a distinct binary code, and no code is a prefix of any other code.
Suppose that the code for symbol s_1 is a prefix of the code for symbol s_2.
Since it is a prefix of the code for s_1, it must pass through the leaf labeled s_1, which is a contradiction, since a leaf has no children.
www.cs.cmu.edu /People/cburch/211-sp96/6Mar.html   (992 words)

 An Introduction to Data Compression
prefix: almost the same as a string, but with the implication that a prefix immediately precedes a character, and a prefix can have a length of zero.
It is possible that this code will not be in the string table, but let's assume for now that it is. Output the string corresponding to <code> to the codestream.
The packaging of codes into a bitsream for the raster data is also a potential stumbling block for the novice encoder or decoder.
www.cis.udel.edu /~amer/CISC651/lzw.and.gif.explained.html   (2491 words)

 New Area Code, Prefix for HSC Phone Numbers
The area code and prefix changes will not affect campus five-digit dialing, however, and the current (213) 342-XXXX HSC phone numbers will continue to work from off-campus until Jan. 16, 1999, also the end of the grace period for the area code split.
The move to a new 442 prefix for HSC was prompted by the upcoming split of the 213 area code, said Larry Nelson, telecommunications manager for USC's Information Services Division (formerly telecommunications).
Area code 818 was recently split into 818 and 626; area code 714 will soon split into 714 and 949.
www.usc.edu /uscnews/stories/3255.html   (371 words)

 SBC - Help - Area Code Prefixes - Texas
A prefix is the first three numbers after your area code.
This site displays prefix lists for area codes within Indiana that are currently undergoing a change or very recently have changed.
Since there are no required telephone number changes with an overlay area code, prefix lists are not maintained for those areas that will have a new overlay area code added.
www.sbc.com /gen/general?pid=1529   (230 words)

 prefix code   (Site not responding. Last check: 2007-10-21)
Definition: Set of words such that no word of the set is a prefix of another word in the set.
A prefix code may be represented by a coding tree.
Algorithms and Theory of Computation Handbook, CRC Press LLC, 1999, "prefix code", from Dictionary of Algorithms and Data Structures, Paul E. Black, ed., NIST.
www.nist.gov /dads/HTML/prefixcode.html   (121 words)

 [No title]   (Site not responding. Last check: 2007-10-21)
Prefix codes are codes in which no codeword is a prefix of some other codeword.
The codeword structure and optimal substructure of an optimal prefix code imply the correctness of the Huffman code.
Suppose that T is a full binary tree representing an optimal prefix code, and x, y are sibling leaves of T with z as their parent.
www-rcf.usc.edu /~xwang/cs570/usc_restricted/lectures/lect9/outlinee.htm   (313 words)

 [No title]   (Site not responding. Last check: 2007-10-21)
If the alphabet is C, then the binary tree must have C leaves, and exactly C-1 internal nodes (why?) (Given a tree T corresponding to a prefix code, it is easy to compute the number of bits required to encode a file.
Then, the number of bits to encode a file is B(T) =  EMBED Equation.3  Constructing a Huffman code Huffman invented a greedy algorithm that constructs an optimal prefix code in a bottom-up manner.
When algorithm terminates, the binary code for a character x is obtained by traversing the tree from root to x and concatenating the 0’s and 1’s assigned to tree edges.
web.umr.edu /~ercal/355/Lectures/Section-16.3-HuffmanCodes.doc   (600 words)

 [No title]   (Site not responding. Last check: 2007-10-21)
NASM assembly code is then generated from // that parse tree.
The primary purpose is to illustrate some principles // of programming languages, but keep in mind that the generated assembly // code is inefficient (primarily because it stores all temporary values // on the run-time stack instead of making good use of registers).
This code leaves the value of the expression // in [esp].
www.cs.colorado.edu /~main/theory/leo/codegen-outline.cxx   (790 words)

 Data Element: International Telephone Number - U.S. Fish & Wildlife Service
The first digit of the country code is always a number from 1 through 9; a leading zero is not permitted.
The following United States territories and associated areas are not part of the NANP and require, at a minimum, an IAC or IDD prefix and a Country Code: American Samoa, the freely associated states of Micronesia and the Marshall Islands, and the trust territory of Palau.
Examples of international dialing codes when calls originate in the United States: American Samoa is 011 + 684 + the local number (city codes are not required); London (inner), United Kingdom is 011 + 44 + 171 + the local number (codes are required for specified cities).
www.fws.gov /stand/standards/de_intertelephone.html   (667 words)

 WTI CAS-161A; Code Activated Switch -- User's Guide
The code sequence is a user-selectable Prefix code and a Port Select code.
The Prefix code is set via the Setup switch on the bottom of the unit.
The procedure for selecting the Prefix Code is described in Section 3.
www.wti.com /guides/cs16_usr.htm   (2068 words)

 [No title]
Prefix coding: Each symbol (possible outcome for random variable) will map to a sequence of bits Prefix code — no code sequence is a prefix of another.
Unique decoding — no confusion By simply reading from left to right If not prefix coded, then if a=000, and b=0001, we can’t tell if a sequence that’s 0001… is supposed to start with a or b.
All prefix codes satisfy the following inequality: Kraft ineq.
www.fas.harvard.edu /~libcs124/E210/classnotes/October15.doc   (325 words)

 BarCode 1 Quick Tour FAQ
As long as the UCC Company Prefix is active, the company is a member of the Uniform Code Council, Inc. Therefore, a company cannot cancel membership and continue to use the UCC Company Prefix.
The prefix code is a way to have 70-plus EAN member organizations issuing numbers without having to worry about duplicate numbers.
The bar code on the backs of some driver licenses, for example, is not UPC and has no guard bars at all.
www.adams1.com /pub/russadam/new.html   (3446 words)

 Prefix code -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-10-21)
In other words, for any given valid (A linear sequence of symbols (characters or words or phrases)) string in the code, there is no shorter string in the code that is an initial substring of that string.
Examples of prefix codes are the variable-length (Click link for more info and facts about Huffman codes) Huffman codes, (Click link for more info and facts about country calling codes) country calling codes, and (Click link for more info and facts about ISBN) ISBNs.
This article is partly derived from (Click link for more info and facts about Federal Standard 1037C) Federal Standard 1037C, which uses the term comma-free code.
www.absoluteastronomy.com /encyclopedia/p/pr/prefix_code.htm   (115 words)

 UCR Area Code/Prefix Change Information
As many of you already know, Riverside will be receiving a new area code (951) beginning July 17, 2004, as mandated by the California Public Utilities Commission.
Beginning October 30, 2004, the 909 area code will no longer be valid for calls destined for campus.
If you have a cellphone with a 909 area code, please check our cellphone information page.
www.cnc.ucr.edu /951   (149 words)

 Java Prefix Free Code Tree   (Site not responding. Last check: 2007-10-21)
Prefix Free Codes or "Prefix Codes" are used to to encode data quickly and efficiently in computer science.
You can trace out the code by moving the curror allong the message text or the encoded text using the arrow keys.
Click on the bright blue icon at the top of the value/path table for more details like the length of the path and the frequency the letter is used in the message.
www.geocities.com /brightyetvague/prog/java/prefix_free/PrefixFreeCodeApplet.html   (226 words)

 Interchange Tags Reference: Looping tags and Sub-tags
PREFIX represents the prefix that is used in that looping tag.
In an [item-list] this is always the product code; in a loop list it is the value of the current argument; in a search it is whatever you have defined as the first mv_return_field (rf).
The default is only to return the code of the search result, but by setting those parameters you can return more than one item.
www.icdevgroup.org /i/dev/dev-4.8/ictags_3.html   (1181 words)

 Telephone Prefix Location List
To find a prefix location in a specific area code, click on the area code to go to the search page for that area code.
If an area code has recently undergone a split you may not find the new area code's listings yet.
If that happens use the area code before the split occurred.
thedirectory.org /pref   (433 words)

 Telephone Prefix Search in Area Code 213
If you know of a prefix we do not have or you spot an error, let us know but don't get upset about it.
This prefix list is updated on a regular basis.
We know about ALL new area codes long before they are implemented.
www.thedirectory.org /pref/search/213.htm   (207 words)

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