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. The tables may be precalculated and stored in static program storage, calculated 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 items in an array and, in some programming languages, may include pointer functions to process the matching input. FPGAs also make extensive use of reconfigurable, hardware-implemented, lookup tables to provide programmable hardware functionality. LUTs differ from hash tables in a way that, to retrieve a value with key , a hash table would store the value in the slot where is a hash function i.e. is used to compute the slot, while in the case of LUT, the value is stored in slot , thus directly addressable.

A field-programmable gate array (FPGA) is a type of configurable integrated circuit that can be programmed or reprogrammed after manufacturing. FPGAs are part of a broader set of logic devices referred to as programmable logic devices (PLDs). They consist of an array of programmable logic blocks and interconnects that can be configured to perform various digital functions. FPGAs are commonly used in applications where flexibility, speed, and parallel processing capabilities are required, such as in telecommunications, automotive, aerospace, and industrial sectors.