What is lookup?

  • (noun): An operation that determines whether one or more of a set of items has a specified property.
    Example: "They wrote a program to do a table lookup"
    Synonyms: search


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 program's 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.

Read more about Lookup.

Some articles on lookup:

Other Usage of Lookup Tables - Hardware LUTs
... In digital logic, an n-bit lookup table can be implemented with a multiplexer whose select lines are the inputs of the LUT and whose inputs are constants ...
... commands involved with Nbtstat that allows several options such as local cache lookup, WINS server query, broadcast, LMHOSTS lookup, Hosts lookup, and it is not for DNS server query ...
Barton–Nackman Trick - How It Works
... are of type value_type, it attempts argument-dependent lookup (ADL) for operator== ... This lookup includes consideration of friend functions declared in value_type and its base classes ... Eventually, the rules for argument-dependent lookup were adjusted to replace friend name injection by a less drastic mechanism, described above, that maintained the validity ...
FPS AP-120B - Architecture - Lookup Tables
... hardware was delivered with a pre-calculated lookup table of sine and cosine values ... for all other angles could be calculated by using one or other of the values from the lookup table, negating if necessary, using well-known rules ...
SQL Server Integration Services - Features - Features of The Data Flow Task
... Split Multicast Union-All, Merge, and Merge Join Sort Fuzzy Grouping Lookup and Fuzzy Lookup Percentage Sampling and Row Sampling Transformation ... DB Command Row Count Term Extraction Term Lookup Row Sampling The Conditional Split transformation is used to conditionally route rows to other transformation objects based on a particular condition ...