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55-507: Kaillera was developed by Christophe Thibault in the years 2001–2006. His most recent entry was the Kaillera Client library and SDK on 13 February 2002. Later in early 2006, rights and source code of Kaillera were sold to a private online gaming advertising company called TC. Ads and Etai Hugi. On 17 June 2006, Christophe Thibault himself publicly confirmed the sale of Kaillera and also announced that TC. Ads. no longer had anything to do with

110-492: A code obfuscation technique as a measure against disassembly and tampering. The principle is also used in shared code sequences of fat binaries which must run on multiple instruction-set-incompatible processor platforms. This property is also used to find unintended instructions called gadgets in existing code repositories and is used in return-oriented programming as alternative to code injection for exploits such as return-to-libc attacks . In some computers,

165-441: A compiler or an assembler . The resulting executable is machine code ready for the computer. Alternatively, source code can be executed without conversion via an interpreter . An interpreter loads the source code into memory. It simultaneously translates and executes each statement . A method that combines compilation and interpretation is to first produce bytecode . Bytecode is an intermediate representation of source code that

220-462: A source-code editor that can alert the programmer to common errors. Modification often includes code refactoring (improving the structure without changing functionality) and restructuring (improving structure and functionality at the same time). Nearly every change to code will introduce new bugs or unexpected ripple effects , which require another round of fixes. Code reviews by other developers are often used to scrutinize new code added to

275-430: A trade secret . Proprietary, secret source code and algorithms are widely used for sensitive government applications such as criminal justice , which results in black box behavior with a lack of transparency into the algorithm's methodology. The result is avoidance of public scrutiny of issues such as bias. Access to the source code (not just the object code) is essential to modifying it. Understanding existing code

330-529: A bottleneck. This led to the introduction of high-level programming languages such as Fortran in the mid-1950s. These languages abstracted away the details of the hardware, instead being designed to express algorithms that could be understood more easily by humans. As instructions distinct from the underlying computer hardware , software is therefore relatively recent, dating to these early high-level programming languages such as Fortran , Lisp , and Cobol . The invention of high-level programming languages

385-416: A direct map between the numerical machine code and a human-readable mnemonic. In assembly, numerical opcodes and operands are replaced with mnemonics and labels. For example, the x86 architecture has available the 0x90 opcode; it is represented as NOP in the assembly source code . While it is possible to write programs directly in machine code, managing individual bits and calculating numerical addresses

440-486: A machine with a single accumulator , the accumulator is implicitly both the left operand and result of most arithmetic instructions. Some other architectures, such as the x86 architecture, have accumulator versions of common instructions, with the accumulator regarded as one of the general registers by longer instructions. A stack machine has most or all of its operands on an implicit stack. Special purpose instructions also often lack explicit operands; for example, CPUID in

495-581: A manner befitting user's ping and connection configuration. Note 1: There are several third-party versions of MAME with Kaillera, but these violate the MAME license by not having the source code to the Kaillera client library distributed, even though the source code to the modified version of MAME itself (such as "MAME32k", "MAME32 Plus! Plus!" and "MameLang32+") are always provided. Source code In computing , source code , or simply code or source ,

550-433: A one-to-one mapping to machine code. The assembly language decoding method is called disassembly . Machine code may be decoded back to its corresponding high-level language under two conditions: The first condition is to accept an obfuscated reading of the source code. An obfuscated version of source code is displayed if the machine code is sent to a decompiler of the source language. The second condition requires

605-400: A paging based system, if the current page actually holds machine code by an execute bit — pages have multiple such permission bits (readable, writable, etc.) for various housekeeping functionality. E.g. on Unix-like systems memory pages can be toggled to be executable with the mprotect() system call, and on Windows, VirtualProtect() can be used to achieve a similar result. If an attempt

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660-444: A project. The purpose of this phase is often to verify that the code meets style and maintainability standards and that it is a correct implementation of the software design . According to some estimates, code review dramatically reduce the number of bugs persisting after software testing is complete. Along with software testing that works by executing the code, static program analysis uses automated tools to detect problems with

715-406: A specific platform, source code can be ported to a different machine and recompiled there. For the same source code, object code can vary significantly—not only based on the machine for which it is compiled, but also based on performance optimization from the compiler. Most programs do not contain all the resources needed to run them and rely on external libraries . Part of the compiler's function

770-444: A tag and a Y field. In addition to transfer (branch) instructions, these machines have skip instruction that conditionally skip one or two words, e.g., Compare Accumulator with Storage (CAS) does a three way compare and conditionally skips to NSI, NSI+1 or NSI+2, depending on the result. The MIPS architecture provides a specific example for a machine code whose instructions are always 32 bits long. The general type of instruction

825-405: Is a plain text computer program written in a programming language . A programmer writes the human readable source code to control the behavior of a computer . Since a computer, at base, only understands machine code , source code must be translated before a computer can execute it. The translation process can be implemented three ways. Source code can be converted into machine code by

880-442: Is an overarching term that can refer to a code's correct and efficient behavior, its reusability and portability , or the ease of modification. It is usually more cost-effective to build quality into the product from the beginning rather than try to add it later in the development process. Higher quality code will reduce lifetime cost to both suppliers and customers as it is more reliable and easier to maintain . Maintainability

935-452: Is frequently cited as a contributing factor to the maturation of their programming skills. Some people consider source code an expressive artistic medium . Source code often contains comments —blocks of text marked for the compiler to ignore. This content is not part of the program logic, but is instead intended to help readers understand the program. Companies often keep the source code confidential in order to hide algorithms considered

990-477: Is generally different from bytecode (also known as p-code), which is either executed by an interpreter or itself compiled into machine code for faster (direct) execution. An exception is when a processor is designed to use a particular bytecode directly as its machine code, such as is the case with Java processors . Machine code and assembly code are sometimes called native code when referring to platform-dependent parts of language features or libraries. From

1045-449: Is given by the op (operation) field, the highest 6 bits. J-type (jump) and I-type (immediate) instructions are fully specified by op . R-type (register) instructions include an additional field funct to determine the exact operation. The fields used in these types are: rs , rt , and rd indicate register operands; shamt gives a shift amount; and the address or immediate fields contain an operand directly. For example, adding

1100-500: Is implemented as a small library with a typical GUI which is incorporated with the emulator. Its simple self-explanatory API , consisting of only eight functions, allows emulators to perform necessary functions such as specifying the list of supported games and controlling game execution to some extent. Everything after enabling the client to starting the game is managed by the client and the user. The client can only make requests to server on user's input and react to server's response. On

1155-428: Is made to execute machine code on a non-executable page, an architecture specific fault will typically occur. Treating data as machine code , or finding new ways to use existing machine code, by various techniques, is the basis of some security vulnerabilities. Similarly, in a segment based system, segment descriptors can indicate whether a segment can contain executable code and in what rings that code can run. From

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1210-496: Is necessary to understand how it works and before modifying it. The rate of understanding depends both on the code base as well as the skill of the programmer. Experienced programmers have an easier time understanding what the code does at a high level. Software visualization is sometimes used to speed up this process. Many software programmers use an integrated development environment (IDE) to improve their productivity. IDEs typically have several features built in, including

1265-470: Is quickly interpreted. The first programmable computers, which appeared at the end of the 1940s, were programmed in machine language (simple instructions that could be directly executed by the processor). Machine language was difficult to debug and was not portable between different computer systems. Initially, hardware resources were scarce and expensive, while human resources were cheaper. As programs grew more complex, programmer productivity became

1320-425: Is rarely a problem. Systems may also differ in other details, such as memory arrangement, operating systems, or peripheral devices . Because a program normally relies on such factors, different systems will typically not run the same machine code, even when the same type of processor is used. A processor's instruction set may have fixed-length or variable-length instructions. How the patterns are organized varies with

1375-512: Is tedious and error-prone. Therefore, programs are rarely written directly in machine code. However, an existing machine code program may be edited if the assembly source code is not available. The majority of programs today are written in a high-level language . A high-level program may be translated into machine code by a compiler . Every processor or processor family has its own instruction set . Instructions are patterns of bits , digits, or characters that correspond to machine commands. Thus,

1430-617: Is that many software engineering courses do not emphasize it. Development engineers who know that they will not be responsible for maintaining the software do not have an incentive to build in maintainability. The situation varies worldwide, but in the United States before 1974, software and its source code was not copyrightable and therefore always public domain software . In 1974, the US Commission on New Technological Uses of Copyrighted Works (CONTU) decided that "computer programs, to

1485-558: Is the binary representation of a computer program which is actually read and interpreted by the computer. A program in machine code consists of a sequence of machine instructions (possibly interspersed with data). Each machine code instruction causes the CPU to perform a specific task. Examples of such tasks include: In general, each architecture family (e.g., x86 , ARM ) has its own instruction set architecture (ISA), and hence its own specific machine code language. There are exceptions, such as

1540-477: Is the quality of software enabling it to be easily modified without breaking existing functionality. Following coding conventions such as using clear function and variable names that correspond to their purpose makes maintenance easier. Use of conditional loop statements only if the code could execute more than once, and eliminating code that will never execute can also increase understandability. Many software development organizations neglect maintainability during

1595-418: Is to link these files in such a way that the program can be executed by the hardware. Software developers often use configuration management to track changes to source code files ( version control ). The configuration management system also keeps track of which object code file corresponds to which version of the source code file. The number of lines of source code is often used as a metric when evaluating

1650-419: Is typically set to a hard coded value when the CPU is first powered on, and will hence execute whatever machine code happens to be at this address. Similarly, the program counter can be set to execute whatever machine code is at some arbitrary address, even if this is not valid machine code. This will typically trigger an architecture specific protection fault. The CPU is oftentimes told, by page permissions in

1705-534: The Kruskal count , sometimes possible through opcode-level programming to deliberately arrange the resulting code so that two code paths share a common fragment of opcode sequences. These are called overlapping instructions , overlapping opcodes , overlapping code , overlapped code , instruction scission , or jump into the middle of an instruction . In the 1970s and 1980s, overlapping instructions were sometimes used to preserve memory space. One example were in

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1760-678: The VAX architecture, which includes optional support of the PDP-11 instruction set; the IA-64 architecture, which includes optional support of the IA-32 instruction set; and the PowerPC 615 microprocessor, which can natively process both PowerPC and x86 instruction sets. Machine code is a strictly numerical language, and it is the lowest-level interface to the CPU intended for a programmer. Assembly language  provides

1815-591: The Zilog Z80 processor, the machine code 00000101 , which causes the CPU to decrement the B general-purpose register , would be represented in assembly language as DEC B . The IBM 704, 709, 704x and 709x store one instruction in each instruction word; IBM numbers the bit from the left as S, 1, ..., 35. Most instructions have one of two formats: For all but the IBM 7094 and 7094 II, there are three index registers designated A, B and C; indexing with multiple 1 bits in

1870-409: The Kaillera project and that Etai Hugi is the only owner. On 20 November 2006, Etai Hugi announced that a new version of Kaillera would be released in "the next several months". His announcement also suggested that the new version would be "much better" and "more efficient" than the current version. In July 2007, he posted on the official forums and sent emails to the forum administrator announcing that

1925-426: The development phase, even though it will increase long-term costs. Technical debt is incurred when programmers, often out of laziness or urgency to meet a deadline, choose quick and dirty solutions rather than build maintainability into their code. A common cause is underestimates in software development effort estimation , leading to insufficient resources allocated to development. A challenge with maintainability

1980-406: The extent that they embody an author's original creation, are proper subject matter of copyright". Proprietary software is rarely distributed as source code. Although the term open-source software literally refers to public access to the source code , open-source software has additional requirements: free redistribution, permission to modify the source code and release derivative works under

2035-464: The implementation of error tables in Microsoft 's Altair BASIC , where interleaved instructions mutually shared their instruction bytes. The technique is rarely used today, but might still be necessary to resort to in areas where extreme optimization for size is necessary on byte-level such as in the implementation of boot loaders which have to fit into boot sectors . It is also sometimes used as

2090-511: The instruction set is specific to a class of processors using (mostly) the same architecture . Successor or derivative processor designs often include instructions of a predecessor and may add new additional instructions. Occasionally, a successor design will discontinue or alter the meaning of some instruction code (typically because it is needed for new purposes), affecting code compatibility to some extent; even compatible processors may show slightly different behavior for some instructions, but this

2145-475: The instructions can be carried out. After being compiled, the program can be saved as an object file and the loader (part of the operating system) can take this saved file and execute it as a process on the computer hardware. Some programming languages use an interpreter instead of a compiler. An interpreter converts the program into machine code at run time , which makes them 10 to 100 times slower than compiled programming languages. Software quality

2200-519: The machine code of the architecture is implemented by an even more fundamental underlying layer called microcode , providing a common machine language interface across a line or family of different models of computer with widely different underlying dataflows . This is done to facilitate porting of machine language programs between different models. An example of this use is the IBM System/360 family of computers and their successors. Machine code

2255-456: The next official release would occur in "3–4 months." This announcement coincided with a revamp of the forums and the posting of new unofficial builds created by others for download (the first new downloads posted in nearly four years). On 4 November 2007, it was announced that due to unforeseen "bugs" the imminent release would be postponed for a time. It was later announced that the new version of Kaillera would be released on 7 April 2008. However,

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2310-442: The official Kaillera website along with existing Kaillera master servers list was taken down a few days prior to the release date. Later when it came back up, no explanations for the downtime was given and nothing was released. Etai Hugi an Israeli developer purchased Kaillera from Christophe Thibault in 2006. Like most networked multiplayer gaming systems, Kaillera is implemented to work on client–server architecture . The client

2365-412: The other four index registers. The effective address is normally Y-C(T), where C(T) is either 0 for a tag of 0, the logical or of the selected index regisrs in multiple tag mode or the selected index register if not in multiple tag mode. However, the effective address for index register control instructions is just Y. A flag with both bits 1 selects indirect addressing; the indirect address word has both

2420-431: The other hand, the server takes the tedious role of managing all the users. Users can join servers if their conditions are satisfactory. Then they are allowed to chat and make games on the server which other users can join. A maximum of 8 players are allowed to participate in a game and others are treated as spectators. Once a game starts, the server is also responsible for scheduling and mix matching data sent by emulators in

2475-529: The particular architecture and type of instruction. Most instructions have one or more opcode fields that specify the basic instruction type (such as arithmetic, logical, jump , etc.), the operation (such as add or compare), and other fields that may give the type of the operand (s), the addressing mode (s), the addressing offset(s) or index, or the operand value itself (such constant operands contained in an instruction are called immediate ). Not all machines or individual instructions have explicit operands. On

2530-657: The point of view of a process , the code space is the part of its address space where the code in execution is stored. In multitasking systems this comprises the program's code segment and usually shared libraries . In multi-threading environment, different threads of one process share code space along with data space, which reduces the overhead of context switching considerably as compared to process switching. Various tools and methods exist to decode machine code back to its corresponding source code . Machine code can easily be decoded back to its corresponding assembly language source code because assembly language forms

2585-501: The point of view of the CPU, machine code is stored in RAM, but is typically also kept in a set of caches for performance reasons. There may be different caches for instructions and data, depending on the architecture. The CPU knows what machine code to execute, based on its internal program counter. The program counter points to a memory address and is changed based on special instructions which may cause programmatic branches. The program counter

2640-465: The productivity of computer programmers, the economic value of a code base, effort estimation for projects in development, and the ongoing cost of software maintenance after release. Source code is also used to communicate algorithms between people – e.g., code snippets online or in books. Computer programmers may find it helpful to review existing source code to learn about programming techniques. The sharing of source code between developers

2695-412: The registers 1 and 2 and placing the result in register 6 is encoded: Load a value into register 8, taken from the memory cell 68 cells after the location listed in register 3: Jumping to the address 1024: On processor architectures with variable-length instruction sets (such as Intel 's x86 processor family) it is, within the limits of the control-flow resynchronizing phenomenon known as

2750-416: The result of a constant expression freed up by replacing it by that constant) and other code enhancements. A much more human-friendly rendition of machine language, named assembly language , uses mnemonic codes to refer to machine code instructions, rather than using the instructions' numeric values directly, and uses symbolic names to refer to storage locations and sometimes registers . For example, on

2805-427: The same license, and nondiscrimination between different uses—including commercial use. The free reusability of open-source software can speed up development. Machine language In computer programming , machine code is computer code consisting of machine language instructions , which are used to control a computer's central processing unit (CPU). For conventional binary computers , machine code

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2860-414: The source code. Many IDEs support code analysis tools, which might provide metrics on the clarity and maintainability of the code. Debuggers are tools that often enable programmers to step through execution while keeping track of which source code corresponds to each change of state. Source code files in a high-level programming language must go through a stage of preprocessing into machine code before

2915-443: The tag subtracts the logical or of the selected index registers and loading with multiple 1 bits in the tag loads all of the selected index registers. The 7094 and 7094 II have seven index registers, but when they are powered on they are in multiple tag mode , in which they use only the three of the index registers in a fashion compatible with earlier machines, and require a Leave Multiple Tag Mode ( LMTM ) instruction in order to access

2970-406: The x86 architecture writes values into four implicit destination registers. This distinction between explicit and implicit operands is important in code generators, especially in the register allocation and live range tracking parts. A good code optimizer can track implicit and explicit operands which may allow more frequent constant propagation , constant folding of registers (a register assigned

3025-480: Was simultaneous with the compilers needed to translate the source code automatically into machine code that can be directly executed on the computer hardware . Source code is the form of code that is modified directly by humans, typically in a high-level programming language. Object code can be directly executed by the machine and is generated automatically from the source code, often via an intermediate step, assembly language . While object code will only work on

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