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Perl Virtual Machine
The Perl virtual machine is a stack-based process virtual machine implemented as an opcodes interpreter which runs previously compiled programs written in the Perl language. The opcodes interpreter is a part of the Perl interpreter, which also contains a compiler ( lexer, parser and optimizer) in one executable file, commonly /usr/bin/perl on various Unix-like systems or perl.exe on Microsoft Windows systems. Implementation Opcodes The Perl compiler outputs a compiled program into memory as an internal structure which can be represented as a tree graph in which each node represents an opcode. Opcodes are represented internally by typedefs. Each opcode has ''next'' / ''other'' and ''first'' / ''sibling'' pointers, so the opcode tree can be drawn as a basic OP tree starting from root node or as flat OP list in the order they would normally execute from start node. Opcodes tree can be mapped to the source code, so it is possible to decompile to high-level source code. Perl's opcodes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stack Machine
In computer science, computer engineering and programming language implementations, a stack machine is a computer processor or a Virtual machine#Process virtual machines, process virtual machine in which the primary interaction is moving short-lived temporary values to and from a push down Stack (abstract data type), stack. In the case of a hardware processor, a hardware stack is used. The use of a stack significantly reduces the required number of processor registers. Stack machines extend push-down automata with additional load/store operations or multiple stacks and hence are Turing-complete. Design Most or all stack machine instructions assume that operands will be from the stack, and results placed in the stack. The stack easily holds more than two inputs or more than one result, so a rich set of operations can be computed. In stack machine code (sometimes called p-code), instructions will frequently have only an opcode commanding an operation, with no additional fields i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microsoft Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sectors of the computing industry – Windows (unqualified) for a consumer or corporate workstation, Windows Server for a Server (computing), server and Windows IoT for an embedded system. Windows is sold as either a consumer retail product or licensed to Original equipment manufacturer, third-party hardware manufacturers who sell products Software bundles, bundled with Windows. The first version of Windows, Windows 1.0, was released on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces (GUIs). The name "Windows" is a reference to the windowing system in GUIs. The 1990 release of Windows 3.0 catapulted its market success and led to various other product families ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scope (programming)
In computer programming, the scope of a name binding (an association of a name to an entity, such as a variable) is the part of a program where the name binding is valid; that is, where the name can be used to refer to the entity. In other parts of the program, the name may refer to a different entity (it may have a different binding), or to nothing at all (it may be unbound). Scope helps prevent name collisions by allowing the same name to refer to different objects – as long as the names have separate scopes. The scope of a name binding is also known as the visibility of an entity, particularly in older or more technical literature—this is in relation to the referenced entity, not the referencing name. The term "scope" is also used to refer to the set of ''all'' name bindings that are valid within a part of a program or at a given point in a program, which is more correctly referred to as ''context'' or ''environment''. Strictly speaking and in practice for most programmi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Regular Expression
A regular expression (shortened as regex or regexp), sometimes referred to as rational expression, is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation. Regular expression techniques are developed in theoretical computer science and formal language theory. The concept of regular expressions began in the 1950s, when the American mathematician Stephen Cole Kleene formalized the concept of a regular language. They came into common use with Unix text-processing utilities. Different syntaxes for writing regular expressions have existed since the 1980s, one being the POSIX standard and another, widely used, being the Perl syntax. Regular expressions are used in search engines, in search and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK, and in lexical analysis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reference Counting
In computer science, reference counting is a programming technique of storing the number of references, pointers, or handles to a resource, such as an object, a block of memory, disk space, and others. In garbage collection algorithms, reference counts may be used to deallocate objects that are no longer needed. Advantages and disadvantages The main advantage of the reference counting over tracing garbage collection is that objects are reclaimed ''as soon as'' they can no longer be referenced, and in an incremental fashion, without long pauses for collection cycles and with clearly defined lifetime of every object. In real-time applications or systems with limited memory, this is important to maintain responsiveness. Reference counting is also among the simplest forms of memory management to implement. It also allows for effective management of non-memory resources such as operating system objects, which are often much scarcer than memory (tracing garbage collection systems ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Typeglob
The structure of the Perl programming language encompasses both the syntactical rules of the language and the general ways in which programs are organized. Perl's design philosophy is expressed in the commonly cited motto "there's more than one way to do it". As a multi-paradigm, dynamically typed language, Perl allows a great degree of flexibility in program design. Perl also encourages modularization; this has been attributed to the component-based design structure of its Unix roots, and is responsible for the size of the CPAN archive, a community-maintained repository of more than 100,000 modules. Basic syntax In Perl, the minimal Hello World program may be written as follows: print "Hello, World!\n" This prints the string ''Hello, World!'' and a newline, symbolically expressed by an n character whose interpretation is altered by the preceding escape character (a backslash). Since version 5.10, the new 'say' builtin produces the same effect even more simply: say "Hello, Wo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
"Hello, World!" Program
A "Hello, World!" program is usually a simple computer program that emits (or displays) to the screen (often the Console application, console) a message similar to "Hello, World!". A small piece of code in most general-purpose programming languages, this program is used to illustrate a language's basic Syntax (programming languages), syntax. Such a program is often the first written by a student of a new programming language, but it can also be used as a sanity check to ensure that the computer software intended to Compiler, compile or run source code is correctly installed, and that its operator understands how to use it. History While several small test programs have existed since the development of programmable computers, the tradition of using the phrase "Hello, World!" as a test message was influenced by an example program in the 1978 book ''The C Programming Language'', with likely earlier use in BCPL. The example program from the book prints , and was inherited from a 197 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decompiler
A decompiler is a computer program that translates an executable file back into high-level source code. Unlike a compiler, which converts high-level code into machine code, a decompiler performs the reverse process. While disassemblers translate executables into assembly language, decompilers go a step further by reconstructing the disassembly into higher-level languages like C. Due to the one-way nature of the compilation process, decompilers usually cannot perfectly recreate the original source code. They often produce obfuscated and less readable code. Introduction Decompilation is the process of transforming executable code into a high-level, human-readable format using a decompiler. This process is commonly used for tasks that involve reverse-engineering the logic behind executable code, such as recovering lost or unavailable source code. Decompilers face inherent challenges due to the loss of critical information during the compilation process, such as variable names, c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Typedef
typedef is a reserved keyword in the programming languages C, C++, and Objective-C. It is used to create an additional name (''alias'') for another data type, but does not create a new type, except in the obscure case of a qualified typedef of an array type where the typedef qualifiers are transferred to the array element type. As such, it is often used to simplify the syntax of declaring complex data structures consisting of struct and union types, although it is also commonly used to provide specific descriptive type names for integer data types of varying sizes. Syntax A ''typedef declaration'' follows the same syntax as declaring any other C identifier. The keyword typedef itself is a specifier which means that while it typically appears at the start of the declaration, it can also appear after the type specifiers or between two of them. In the C standard library and in POSIX specifications, the identifier for the typedef definition is often suffixed with , such as in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix-like
A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like Application software, application is one that behaves like the corresponding List of POSIX commands, Unix command or Unix shell, shell. Although there are general Unix philosophy, philosophies for Unix design, there is no technical standard defining the term, and opinions can differ about the degree to which a particular operating system or application is Unix-like. Some well-known examples of Unix-like operating systems include Linux, FreeBSD and OpenBSD. These systems are often used on servers as well as on personal computers and other devices. Many popular applications, such as the Apache HTTP Server, Apache web server and the Bash (Unix shell), Bash shell, are also designed to be used on Unix-like systems. Definition The Open ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Application Virtual Machine
In computing, a virtual machine (VM) is the virtualization or emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination of the two. Virtual machines differ and are organized by their function, shown here: * '' System virtual machines'' (also called full virtualization VMs, or SysVMs) provide a substitute for a real machine. They provide the functionality needed to execute entire operating systems. A hypervisor uses native execution to share and manage hardware, allowing for multiple environments that are isolated from one another yet exist on the same physical machine. Modern hypervisors use hardware-assisted virtualization, with virtualization-specific hardware features on the host CPUs providing assistance to hypervisors. * '' Process virtual machines'' are designed to execute computer programs in a platform-i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compiler Optimization
An optimizing compiler is a compiler designed to generate code that is optimized in aspects such as minimizing program execution time, memory usage, storage size, and power consumption. Optimization is generally implemented as a sequence of optimizing transformations, a.k.a. compiler optimizations algorithms that transform code to produce semantically equivalent code optimized for some aspect. Optimization is limited by a number of factors. Theoretical analysis indicates that some optimization problems are NP-complete, or even undecidable. Also, producing perfectly ''optimal'' code is not possible since optimizing for one aspect often degrades performance for another. Optimization is a collection of heuristic methods for improving resource usage in typical programs. Categorization Local vs. global scope Scope describes how much of the input code is considered to apply optimizations. Local scope optimizations use information local to a basic block. Since basic blocks cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
