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In computer science, a lookup table (LUT) is an array that replaces runtime computation with a simpler array indexing operation, in a process termed as direct addressing.The savings in processing time can be significant, because retrieving a value from memory is often faster than carrying out an "expensive" computation or input/output operation. [1]
The reason is quite simple: any lookup table that takes an extremely long time to compute also takes up an extremely large amount of space. Space is the fundamental limitation. Say you have a 10 terabyte drive filled with a lookup table and each element takes a microsecond to compute. Then the total time is only 16 weeks, which isn't that bad.
In the film and graphics industries, 3D lookup tables (3D LUTs) are used for color grading and for mapping one color space to another. They are commonly used to calculate preview colors for a monitor or digital projector of how an image will be reproduced on another display device, typically the final digitally projected image or release print ...
The Rijndael S-box is a substitution box (lookup table) used in the Rijndael cipher, on which the Advanced Encryption Standard (AES) cryptographic algorithm is based. [1]
In computer science, an associative array, map, symbol table, or dictionary is an abstract data type that stores a collection of (key, value) pairs, such that each possible key appears at most once in the collection. In mathematical terms, an associative array is a function with finite domain. [1] It supports 'lookup', 'remove', and 'insert ...
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Gal's accurate tables is a method devised by Shmuel Gal to provide accurate values of special functions using a lookup table and interpolation. It is a fast and efficient method for generating values of functions like the exponential or the trigonometric functions to within last-bit accuracy for almost all argument values without using extended ...
An m×n S-box can be implemented as a lookup table with 2 m words of n bits each. Fixed tables are normally used, as in the Data Encryption Standard (DES), but in some ciphers the tables are generated dynamically from the key (e.g. the Blowfish and the Twofish encryption algorithms).