Lookuptabel

Lookuptabel, commonly called a lookup table, is a data structure that stores precomputed values to replace expensive computations with a table lookup. It maps input keys to output values, enabling constant-time retrieval.

In practice, lookuptabels are often implemented as arrays, where the input key serves as the array index. This yields O(1) access and high speed, especially when keys are contiguous integers. For non-numeric or sparse keys, hash-based dictionaries or perfect hash tables may be used to provide fast lookups while controlling collisions.

Static vs dynamic: A static table is filled at initialization and remains unchanged; a dynamic table can be updated at runtime. Some tables are generated offline from data sets or algorithms; others are constructed on demand.

Common applications: character encoding and case conversion, color palettes, precomputed trigonometric values for graphics, CRC and other checksum computations, and data deserialization.

Considerations: memory usage scales with the number of distinct keys; cache locality matters; lookup tables trade memory for speed; if the input domain is large or sparse, alternative structures may be more space-efficient.

Etymology: The term lookup table is widely used in English; lookuptabel is a variant spelling found in some languages or informal contexts. The concept is foundational in computer science and digital design.