Editing Lookup table (section)

== Other usages of lookup tables ==

=== Caches ===
{{main|Cache (computing)}}
Storage caches (including disk caches for files, or processor caches for either code or data) work also like a lookup table. The table is built with very fast memory instead of being stored on slower external memory, and maintains two pieces of data for a sub-range of bits composing an external memory (or disk) address (notably the lowest bits of any possible external address):
* one piece (the tag) contains the value of the remaining bits of the address; if these bits match with those from the memory address to read or write, then the other piece contains the cached value for this address.
* the other piece maintains the data associated to that address.
A single (fast) lookup is performed to read the tag in the lookup table at the index specified by the lowest bits of the desired external storage address, and to determine if the memory address is hit by the cache. When a hit is found, no access to external memory is needed (except for write operations, where the cached value may need to be updated asynchronously to the slower memory after some time, or if the position in the cache must be replaced to cache another address).

=== Hardware LUTs ===
In [[digital logic]], a lookup table can be implemented with a [[multiplexer]] whose select lines are driven by the address signal and whose inputs are the values of the elements contained in the array. These values can either be hard-wired, as in an [[ASIC]] whose purpose is specific to a function, or provided by [[D latch]]es which allow for configurable values. ([[ROM]], [[EPROM]], [[EEPROM]], or [[random-access memory|RAM]].)

An ''n''-bit LUT can encode any ''n''-input [[Boolean function]] by storing the [[truth table]] of the function in the LUT. This is an efficient way of encoding [[Boolean logic]] functions, and LUTs with 4-6 bits of input are in fact the key component of modern [[field-programmable gate array]]s (FPGAs) which provide reconfigurable hardware logic capabilities.

=== Data acquisition and control systems ===
In [[data acquisition]] and [[control system]]s, lookup tables are commonly used to undertake the following operations in:
* The application of [[calibration]] data, so as to apply corrections to uncalibrated measurement or [[setpoint (control system)|setpoint]] values; and
* Undertaking [[measurement unit]] conversion; and
* Performing generic user-defined computations.

In some systems, [[polynomial]]s may also be defined in place of lookup tables for these calculations.