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BCJ (algorithm)
In data compression, BCJ, short for Branch/Call/Jump, refers to a technique that improves the compression of machine code by replacing relative branch addresses with absolute ones. This allows a Lempel–Ziv compressor to identify duplicate targets and more efficiently encode them. On decompression, the inverse filter restores the original encoding. Different BCJ filters are used for different instruction sets, as each use different opcodes for branching. A form of BCJ is seen in Microsoft's cabinet file format from 1996, which filters x86 CALL instructions for the LZX compressor. The 7z and xz file formats implement BCJ for multiple architectures. Delta update techniques like bsdiff and courgette also include a form of BCJ.Colin Percival Colin A. Percival (born 1980) is a Canadian computer scientist and computer security researcher. He completed his undergraduate education at Simon Fraser University and a doctorate at the University of Oxford. While at university he joine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Compression
In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy. No information is lost in lossless compression. Lossy compression reduces bits by removing unnecessary or less important information. Typically, a device that performs data compression is referred to as an encoder, and one that performs the reversal of the process (decompression) as a decoder. The process of reducing the size of a data file is often referred to as data compression. In the context of data transmission, it is called source coding; encoding done at the source of the data before it is stored or transmitted. Source coding should not be confused with channel coding, for error detection and correction or line coding, the means for mapping data onto a signal. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Machine Code
In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a very specific task, such as a load, a store, a jump, or an arithmetic logic unit (ALU) operation on one or more units of data in the CPU's registers or memory. Early CPUs had specific machine code that might break backwards compatibility with each new CPU released. The notion of an instruction set architecture (ISA) defines and specifies the behavior and encoding in memory of the instruction set of the system, without specifying its exact implementation. This acts as an abstraction layer, enabling compatibility within the same family of CPUs, so that machine code written or generated according to the ISA for the family will run on all CPUs in the family, including future CPUs. In general, each architecture family (e.g. x86, ARM) has its own ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Branch (computer Science)
A branch is an instruction in a computer program that can cause a computer to begin executing a different instruction sequence and thus deviate from its default behavior of executing instructions in order. ''Branch'' (or ''branching'', ''branched'') may also refer to the act of switching execution to a different instruction sequence as a result of executing a branch instruction. Branch instructions are used to implement control flow in program loops and conditionals (i.e., executing a particular sequence of instructions only if certain conditions are satisfied). A branch instruction can be either an ''unconditional branch'', which always results in branching, or a ''conditional branch'', which may or may not cause branching depending on some condition. Also, depending on how it specifies the address of the new instruction sequence (the "target" address), a branch instruction is generally classified as ''direct'', ''indirect'' or ''relative'', meaning that the instruction contai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lempel–Ziv
LZ77 and LZ78 are the two lossless data compression algorithms published in papers by Abraham Lempel and Jacob Ziv in 1977 and 1978. They are also known as LZ1 and LZ2 respectively. These two algorithms form the basis for many variations including LZW, LZSS, LZMA and others. Besides their academic influence, these algorithms formed the basis of several ubiquitous compression schemes, including GIF and the DEFLATE algorithm used in PNG and ZIP. They are both theoretically dictionary coders. LZ77 maintains a sliding window during compression. This was later shown to be equivalent to the ''explicit dictionary'' constructed by LZ78—however, they are only equivalent when the entire data is intended to be decompressed. Since LZ77 encodes and decodes from a sliding window over previously seen characters, decompression must always start at the beginning of the input. Conceptually, LZ78 decompression could allow random access to the input if the entire dictionary were known in ad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Instruction Set
In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ''implementation''. In general, an ISA defines the supported instructions, data types, registers, the hardware support for managing main memory, fundamental features (such as the memory consistency, addressing modes, virtual memory), and the input/output model of a family of implementations of the ISA. An ISA specifies the behavior of machine code running on implementations of that ISA in a fashion that does not depend on the characteristics of that implementation, providing binary compatibility between implementations. This enables multiple implementations of an ISA that differ in characteristics such as performance, physical size, and monetary cost (among other things), but that are capable of running the same machine code, so that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cabinet (file Format)
Cabinet (or CAB) is an archive-file format for Microsoft Windows that supports lossless data compression and embedded digital certificates used for maintaining archive integrity. Cabinet files have .cab filename extensions and are recognized by their first four bytes (also called their '' magic number'') ''MSCF''. Cabinet files were known originally as Diamond files. Design A CAB archive can contain up to 65535 ''folders'' (distinct to standard operating system directories), each of which can contain up to 65535 files for a maximum of 4294836225. Internally, each folder is treated as a single compressed block, which provides more efficient compression than individually compressing each file. Every entry in a folder has to be a file. Due to this structure, it is not possible to store empty folders in CAB archives. The following shows an example a CAB file structure, demonstrating the relationship between folders and files: * CAB file ** First folder *** *** ** Second fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XZ Utils
XZ Utils (previously LZMA Utils) is a set of free software command-line lossless data compressors, including the programs lzma and xz, for Unix-like operating systems and, from version 5.0 onwards, Microsoft Windows. For compression/decompression the Lempel–Ziv–Markov chain algorithm (LZMA) is used. XZ Utils started as a Unix port of Igor Pavlov's LZMA- SDK that has been adapted to fit seamlessly into Unix environments and their usual structure and behavior. Features In most cases, xz achieves higher compression rates than alternatives like gzip and bzip2. Decompression speed is higher than bzip2, but lower than gzip. Compression can be much slower than gzip, and is slower than bzip2 for high levels of compression, and is most useful when a compressed file will be used many times. XZ Utils consists of two major components: * , the command-line compressor and decompressor (analogous to gzip) * liblzma, a software library with an API similar to zlib Various command short ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Delta Update
A delta update is a software update that only requires the user to download those parts of the software's code which are new, or have been changed from their previous state, in contrast to having to download the entire program. The use of delta updates can save significant amounts of time and computing bandwidth. The name ''delta'' derives from the mathematical science use of the Greek letter delta, Δ or δ to denote ''change''. By using a delta update, a program can be updated more quickly and efficiently. For example: An auto racing simulation game has a size of 300 megabytes; it is updated to include a new racetrack, and the body of code which inserts the new racetrack into the game has a size of two megabytes; the game may use a delta update, which would require the download of only the two megabytes of new code, instead of a total download of 302 megabytes. Uses Linux Fedora Linux has supported binary delta updates by default using the yum presto plugin since ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Colin Percival
Colin A. Percival (born 1980) is a Canadian computer scientist and computer security researcher. He completed his undergraduate education at Simon Fraser University and a doctorate at the University of Oxford. While at university he joined the FreeBSD project, and achieved some notoriety for discovering a security weakness in Intel's hyper-threading technology. Besides his work in delta compression and the introduction of memory-hard functions, he is also known for developing the Tarsnap online backup service, which became his full-time job. Education Percival began taking mathematics courses at Simon Fraser University (SFU) at age 13, as a student at Burnaby Central Secondary School. He graduated from Burnaby Central and officially enrolled at SFU in 1998. At SFU he studied number theory under Peter Borwein, and competed in the William Lowell Putnam Mathematical Competition, placing in the top 15 in 1998 and as a Putnam Fellow (in the top six) in 1999. From 1998 to 2000 he ran t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Compression Software
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. A datum is an individual value in a collection of data. Data is usually organized into structures such as tables that provide additional context and meaning, and which may themselves be used as data in larger structures. Data may be used as variables in a computational process. Data may represent abstract ideas or concrete measurements. Data is commonly used in scientific research, economics, and in virtually every other form of human organizational activity. Examples of data sets include price indices (such as consumer price index), unemployment rates, literacy rates, and census data. In this context, data represents the raw facts and figures which can be used in such a manner in order to capture the useful information out of it. Dat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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