|
Prefix-free Code
A prefix code is a type of code system distinguished by its possession of the prefix property, which requires that there is no whole code word in the system that is a prefix (initial segment) of any other code word in the system. It is trivially true for fixed-length codes, so only a point of consideration for variable-length codes. For example, a code with code has the prefix property; a code consisting of does not, because "5" is a prefix of "59" and also of "55". A prefix code is a uniquely decodable code: given a complete and accurate sequence, a receiver can identify each word without requiring a special marker between words. However, there are uniquely decodable codes that are not prefix codes; for instance, the reverse of a prefix code is still uniquely decodable (it is a suffix code), but it is not necessarily a prefix code. Prefix codes are also known as prefix-free codes, prefix condition codes and instantaneous codes. Although Huffman coding is just one of many algo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
Code
In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication channel or storage in a storage medium. An early example is an invention of language, which enabled a person, through speech, to communicate what they thought, saw, heard, or felt to others. But speech limits the range of communication to the distance a voice can carry and limits the audience to those present when the speech is uttered. The invention of writing, which converted spoken language into visual symbols, extended the range of communication across space and time. The process of encoding converts information from a source into symbols for communication or storage. Decoding is the reverse process, converting code symbols back into a form that the recipient understands, such as English, Spanish, etc. One reason for coding is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
Variable-length Code
In coding theory, a variable-length code is a code which maps source symbols to a ''variable'' number of bits. The equivalent concept in computer science is '' bit string''. Variable-length codes can allow sources to be compressed and decompressed with ''zero'' error (lossless data compression) and still be read back symbol by symbol. With the right coding strategy, an independent and identically-distributed source may be compressed almost arbitrarily close to its entropy. This is in contrast to fixed-length coding methods, for which data compression is only possible for large blocks of data, and any compression beyond the logarithm of the total number of possibilities comes with a finite (though perhaps arbitrarily small) probability of failure. Some examples of well-known variable-length coding strategies are Huffman coding, Lempel–Ziv coding, arithmetic coding, and context-adaptive variable-length coding. Codes and their extensions The extension of a code is the m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
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 valid code word. Put another way, a set of strings (called "code words") over an alphabet is called a self-synchronizing code if for each string obtained by concatenating two code words, the substring starting at the second symbol and ending at the second-last symbol does not contain any code word as substring. Every self-synchronizing code is a prefix code, but not all prefix codes are self-synchronizing. Other terms for self-synchronizing code are synchronized code or, ambiguously, comma-free code. A self-synchronizing code permits the proper framing of transmitted code words provided that no uncorrected errors occur in the symbol stream; external synchronization is not required. Self-synchronizing codes also allow recovery from uncor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
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 no other instances of "11" before the end. The Fibonacci code is closely related to the Zeckendorf representation, a positional numeral system that uses Zeckendorf's theorem and has the property that no number has a representation with consecutive 1s. The Fibonacci code word for a particular integer is exactly the integer's Zeckendorf representation with the order of its digits reversed and an additional "1" appended to the end. Definition For a number N\!, if d(0),d(1),\ldots,d(k-1),d(k)\! represent the digits of the code word representing N\! then we have: : N = \sum_^ d(i) F(i+2),\textd(k-1)=d(k)=1.\! where is the th Fibonacci number, and so is the th distinct Fibonacci number starting with 1,2,3,5,8,13,\ldots. The last bit d(k) i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
 |
Morse Code
Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one of the early developers of the system adopted for electrical telegraphy. International Morse code encodes the 26 ISO basic Latin alphabet, basic Latin letters to , one Diacritic, accented Latin letter (), the Arabic numerals, and a small set of punctuation and procedural signals (Prosigns for Morse code, prosigns). There is no distinction between upper and lower case letters. Each Morse code symbol is formed by a sequence of ''dits'' and ''dahs''. The ''dit'' duration can vary for signal clarity and operator skill, but for any one message, once the rhythm is established, a beat (music), half-beat is the basic unit of time measurement in Morse code. The duration of a ''dah'' is three times the duration ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
Sentinel Value
In computer programming, a sentinel value (also referred to as a flag value, trip value, rogue value, signal value, or dummy data) is a special value in the context of an algorithm which uses its presence as a condition of termination, typically in a loop or recursive algorithm. The sentinel value is a form of in-band data that makes it possible to detect the end of the data when no out-of-band data (such as an explicit size indication) is provided. The value should be selected in such a way that it is guaranteed to be distinct from all legal data values since otherwise, the presence of such values would prematurely signal the end of the data (the semipredicate problem). A sentinel value is sometimes known as an " Elephant in Cairo", due to a joke where this is used as a physical sentinel. In safe languages, most sentinel values could be replaced with option types, which enforce explicit handling of the exceptional case. Examples Some examples of common sentinel values and t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
Entropy Encoding
In information theory, an entropy coding (or entropy encoding) is any lossless data compression method that attempts to approach the lower bound declared by Shannon's source coding theorem, which states that any lossless data compression method must have an expected code length greater than or equal to the entropy of the source. More precisely, the source coding theorem states that for any source distribution, the expected code length satisfies \operatorname E_ ell(d(x))\geq \operatorname E_ \log_b(P(x))/math>, where \ell is the function specifying the number of symbols in a code word, d is the coding function, b is the number of symbols used to make output codes and P is the probability of the source symbol. An entropy coding attempts to approach this lower bound. Two of the most common entropy coding techniques are Huffman coding and arithmetic coding. If the approximate entropy characteristics of a data stream are known in advance (especially for signal compression), a simple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
Lossless Data Compression
Lossless compression is a class of data compression that allows the original data to be perfectly reconstructed from the compressed data with no loss of information. Lossless compression is possible because most real-world data exhibits Redundancy (information theory), statistical redundancy. By contrast, lossy compression permits reconstruction only of an approximation of the original data, though usually with greatly improved Bit rate#Bitrates in multimedia, compression rates (and therefore reduced media sizes). By operation of the pigeonhole principle, no lossless compression algorithm can shrink the size of all possible data: Some data will get longer by at least one symbol or bit. Compression algorithms are usually effective for human- and machine-readable documents and cannot shrink the size of random data that contain no Redundancy (information theory), redundancy. Different algorithms exist that are designed either with a specific type of input data in mind or with speci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
Truncated Binary Encoding
Truncated binary encoding is an entropy encoding typically used for uniform probability distributions with a finite alphabet. It is parameterized by an alphabet with total size of number ''n''. It is a slightly more general form of binary encoding when ''n'' is not a power of two. If ''n'' is a power of two, then the coded value for 0 ≤ ''x'' < ''n'' is the simple binary code for ''x'' of length log2(''n''). Otherwise let ''k'' = floor(log2(''n'')), such that 2''k'' < ''n'' < 2''k''+1and let ''u'' = 2''k''+1 − ''n''. Truncated binary encoding assigns the first ''u'' symbols codewords of length ''k'' and then assigns the remaining ''n'' − ''u'' symbols the last ''n'' − ''u'' codewords of length ''k'' + 1. Because all the codewords of length ''k'' + 1 consist of an unassigned codeword of length ''k'' with a "0" or "1" appended, the resulting code is a |
|
 |
Asynchronous Transfer Mode
Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by the American National Standards Institute and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of the Broadband Integrated Services Digital Network as defined in the late 1980s, and designed to integrate telecommunication networks. It can handle both traditional high-throughput data traffic and Real-time computing, real-time, low-latency content such as telephony (voice) and video.ATM Forum, The User Network Interface (UNI), v. 3.1, , Prentice Hall PTR, 1995, page 2. ATM is a cell switching technology, providing functionality that combines features of circuit switching and packet switching networks by using asynchronous communication, asynchronous time-division multiplexing.McDysan (1999), p. 287. ATM was seen in the 1990s as a competitor to Ethernet and networ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
UTF-32/UCS-4
UTF-32 (32- bit Unicode Transformation Format), sometimes called UCS-4, is a fixed-length encoding used to encode Unicode code points that uses exactly 32 bits (four bytes) per code point (but a number of leading bits must be zero as there are far fewer than 232 Unicode code points, needing actually only 21 bits). In contrast, all other Unicode transformation formats are variable-length encodings. Each 32-bit value in UTF-32 represents one Unicode code point and is exactly equal to that code point's numerical value. The main advantage of UTF-32 is that the Unicode code points are directly indexed. Finding the ''Nth'' code point in a sequence of code points is a constant-time operation. In contrast, a variable-length code requires linear-time to count ''N'' code points from the start of the string. This makes UTF-32 a simple replacement in code that uses integers that are incremented by one to examine each location in a string, as was commonly done for ASCII. However, Unicode code ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
|
|
ISO 8859-15
ISO/IEC 8859-15:1999, ''Information technology — 8-bit single-byte coded graphic character sets — Part 15: Latin alphabet No. 9'', is part of the ISO/IEC 8859 series of ASCII-based standard character encodings, first edition published in 1999. It is informally referred to as Latin-9 (and for a while Latin-0). It is similar to ISO 8859-1, and thus also intended for “Western European” languages, but replaces some less common symbols with the euro sign and some letters that were deemed necessary. ISO-8859-15 is the IANA preferred charset name for this standard when supplemented with the C0 and C1 control codes from ISO/IEC 6429. Microsoft has assigned code page 28605 a.k.a. Windows-28605 to ISO-8859-15. IBM has assigned code page 923 ( CCSID 923) to ISO 8859-15. All the printable characters from both ISO/IEC 8859-1 and ISO/IEC 8859-15 are also found in Windows-1252. Since October 2016, less than 0.1% (actually currently less than 0.02%) of all web sites use ISO-8859-15 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |