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Type Punning
In computer science, a type punning is any programming technique that subverts or circumvents the type system of a programming language in order to achieve an effect that would be difficult or impossible to achieve within the bounds of the formal language. In C and C++, constructs such as pointer type conversion and union — C++ adds reference type conversion and reinterpret_cast to this list — are provided in order to permit many kinds of type punning, although some kinds are not actually supported by the standard language. In the Pascal programming language, the use of records with variants may be used to treat a particular data type in more than one manner, or in a manner not normally permitted. Sockets example One classic example of type punning is found in the Berkeley sockets interface. The function to bind an opened but uninitialized socket to an IP address is declared as follows: int bind(int sockfd, struct sockaddr *my_addr, socklen_t addrlen); The bind ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Science
Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to practical disciplines (including the design and implementation of hardware and software). Computer science is generally considered an area of academic research and distinct from computer programming. Algorithms and data structures are central to computer science. The theory of computation concerns abstract models of computation and general classes of problems that can be solved using them. The fields of cryptography and computer security involve studying the means for secure communication and for preventing security vulnerabilities. Computer graphics and computational geometry address the generation of images. Programming language theory considers different ways to describe computational processes, and database theory concerns the management of repositories o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sign Bit
In computer science, the sign bit is a bit in a signed number representation that indicates the sign of a number. Although only signed numeric data types have a sign bit, it is invariably located in the most significant bit position, so the term may be used interchangeably with "most significant bit" in some contexts. Almost always, if the sign bit is 0, the number is non-negative (positive or zero). If the sign bit is 1 then the number is negative, although formats other than two's complement integers allow a signed zero: distinct "positive zero" and "negative zero" representations, the latter of which does not correspond to the mathematical concept of a negative number. In the two's complement representation, the sign bit has the weight where is the number of bits. In the ones' complement representation, the most negative value is , but there are two representations of zero, one for each value of the sign bit. In a sign-and-magnitude representation of numbers, the value ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stride Of An Array
In computer programming, the stride of an array (also referred to as increment, pitch or step size) is the number of locations in memory between beginnings of successive array elements, measured in bytes or in units of the size of the array's elements. The stride cannot be smaller than the element size but can be larger, indicating extra space between elements. An array with stride of exactly the same size as the size of each of its elements is contiguous in memory. Such arrays are sometimes said to have unit stride. Unit stride arrays are sometimes more efficient than non-unit stride arrays, but non-unit stride arrays can be more efficient for 2D or multi-dimensional arrays, depending on the effects of caching and the access patterns used . This can be attributed to the principle of locality, specifically ''spatial locality''. Reasons for non-unit stride Arrays may have a stride larger than their elements' width in bytes in at least three cases: Padding Many languages (inclu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Undefined Behavior
In computer programming, undefined behavior (UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres. This is different from unspecified behavior, for which the language specification does not prescribe a result, and implementation-defined behavior that defers to the documentation of another component of the platform (such as the ABI or the translator documentation). In the C community, undefined behavior may be humorously referred to as "nasal demons", after a comp.std.c post that explained undefined behavior as allowing the compiler to do anything it chooses, even "to make demons fly out of your nose". Overview Some programming languages allow a program to operate differently or even have a different control flow than the source code, as long as it exhibits the same user-visible side effects, ''if undefined behavior never happens during program execution''. Undefined behav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unspecified Behavior
Unspecified behavior is behavior that may vary on different implementations of a programming language. A program can be said to contain unspecified behavior when its source code may produce an executable that exhibits different behavior when compiled on a different compiler, or on the same compiler with different settings, or indeed in different parts of the same executable. While the respective language standards or specifications may impose a range of possible behaviors, the exact behavior depends on the implementation and may not be completely determined upon examination of the program's source code.ISO/IEC (2009-05-29). ''ISO/IEC PDTR 24772.2: Guidance to Avoiding Vulnerabilities in Programming Languages through Language Selection and Use'' Unspecified behavior will often not manifest itself in the resulting program's external behavior, but it may sometimes lead to differing outputs or results, potentially causing portability problems. Definition To enable compilers to produc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aliasing (computing)
In computing, aliasing describes a situation in which a data location in memory can be accessed through different symbolic names in the program. Thus, modifying the data through one name implicitly modifies the values associated with all aliased names, which may not be expected by the programmer. As a result, aliasing makes it particularly difficult to understand, analyze and optimize programs. Aliasing analysers intend to make and compute useful information for understanding aliasing in programs. Examples Buffer overflow For example, most implementations of the C programming language do not perform array bounds checking. One can then exploit the implementation of the programming language by the compiler and the computer architecture's assembly language conventions, to achieve aliasing effects by writing outside of the array (a type of buffer overflow). This invokes undefined behaviour according to the C language specification; however many implementations of C will show th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Structure Alignment
Data structure alignment is the way data is arranged and accessed in computer memory. It consists of three separate but related issues: data alignment, data structure padding, and packing. The CPU in modern computer hardware performs reads and writes to memory most efficiently when the data is ''naturally aligned'', which generally means that the data's memory address is a multiple of the data size. For instance, in a 32-bit architecture, the data may be aligned if the data is stored in four consecutive bytes and the first byte lies on a 4-byte boundary. ''Data alignment'' is the aligning of elements according to their natural alignment. To ensure natural alignment, it may be necessary to insert some ''padding'' between structure elements or after the last element of a structure. For example, on a 32-bit machine, a data structure containing a 16-bit value followed by a 32-bit value could have 16 bits of ''padding'' between the 16-bit value and the 32-bit value to align the 32-bi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quake III
''Quake III Arena'' is a 1999 multiplayer-focused first-person shooter developed by id Software. The third installment of the ''Quake'' series, ''Arena'' differs from previous games by excluding a story-based single-player mode and focusing primarily on multiplayer gameplay. The single-player mode is played against computer-controlled bots. It features music composed by Sonic Mayhem and Front Line Assembly founder Bill Leeb. Notable features of ''Quake III Arena'' include the minimalist design, lacking rarely used items and features; the extensive customizability of player settings such as field of view, texture detail and enemy model; and advanced movement features such as strafe-jumping and rocket-jumping. The game was praised by reviewers who, for the most part, described the gameplay as fun and engaging. Many liked the crisp graphics and focus on multiplayer. ''Quake III Arena'' has also been used extensively in professional electronic sports tournaments such as QuakeCon, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fast Inverse Square Root
Fast inverse square root, sometimes referred to as Fast InvSqrt() or by the hexadecimal constant 0x5F3759DF, is an algorithm that estimates \frac, the reciprocal (or multiplicative inverse) of the square root of a 32-bit floating-point number x in IEEE 754 floating-point format. This operation is used in digital signal processing to normalize a vector, such as scaling it to length 1. For example, computer graphics programs use inverse square roots to compute angles of incidence and reflection for lighting and shading. Predated by similar video game algorithms, this one is best known for its implementation in 1999 in ''Quake III Arena'', a first-person shooter video game heavily based on 3D graphics. The algorithm only started appearing on public forums between 2002 and 2003. Computation of square roots usually depends upon many division operations, which for floating point numbers are computationally expensive. The fast inverse square generates a good approximation with onl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maintainability
In engineering, maintainability is the ease with which a product can be maintained to: * correct defects or their cause, * Repair or replace faulty or worn-out components without having to replace still working parts, * prevent unexpected working conditions, * maximize a product's useful life, * maximize efficiency, reliability, and safety, * meet new requirements, * make future maintenance easier, or * cope with a changing environment. In some cases, maintainability involves a system of continuous improvement - learning from the past to improve the ability to maintain systems, or improve the reliability of systems based on maintenance experience. In telecommunication and several other engineering fields, the term maintainability has the following meanings: * A characteristic of design and installation, expressed as the probability that an item will be retained in or restored to a specified condition within a given period of time, when the maintenance is performed by prescribe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Assertion (computing)
In computer programming, specifically when using the imperative programming paradigm, an assertion is a predicate (a Boolean-valued function over the state space, usually expressed as a logical proposition using the variables of a program) connected to a point in the program, that always should evaluate to true at that point in code execution. Assertions can help a programmer read the code, help a compiler compile it, or help the program detect its own defects. For the latter, some programs check assertions by actually evaluating the predicate as they run. Then, if it is not in fact true – an assertion failure – the program considers itself to be broken and typically deliberately crashes or throws an assertion failure exception. Details The following code contains two assertions, x > 0 and x > 1, and they are indeed true at the indicated points during execution: x = 1; assert x > 0; x++; assert x > 1; Programmers can use assertions to help specify programs and to re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comment (computer Programming)
In computer programming, a comment is a programmer-readable explanation or '' annotation'' in the source code of a computer program. They are added with the purpose of making the source code easier for humans to understand, and are generally ignored by compilers and interpreters.Source code can be divided into ''program code'' (which consists of machine-translatable instructions); and ''comments'' (which include human-readable notes and other kinds of annotations in support of the program code). The syntax of comments in various programming languages varies considerably. Comments are sometimes also processed in various ways to generate documentation external to the source code itself by documentation generators, or used for integration with source code management systems and other kinds of external programming tools. The flexibility provided by comments allows for a wide degree of variability, but formal conventions for their use are commonly part of programming style guides ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
