In computer science, a lookup table is a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than undergoing an 'expensive' computation or input/output operation. The tables may be precalculated and stored in static program storage, calculated (or "pre-fetched") as part of a programs initialization phase (memoization), or even stored in hardware in application-specific platforms. Lookup tables are also used extensively to validate input values by matching against a list of valid (or invalid) items in an array and, in some programming languages, may include pointer functions (or offsets to labels) to process the matching input.
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Famous quotes containing the word table:
“When you got to the table you couldn’t go right to eating, but you had to wait for the widow to tuck down her head and grumble a little over the victuals, though there warn’t really anything the matter with them. That is, nothing only everything was cooked by itself. In a barrel of odds and ends it is different; things get mixed up, and the juice kind of swaps around, and the things go better.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)