Recursive hashing functions for n-grams

Abstract

Many indexing, retrieval, and comparison methods are based on counting or cataloguing n-grams in streams of symbols. The fastest method of implementing such operations is through the use of hash tables. Rapid hashing of consecutive n-grams is best done using a recursive hash function, in which the hash value of the current n-gram is derived from the hash value of its predecessor. This article generalizes recursive hash functions found in the literature and proposes new methods offering superior performance. Experimental results demonstrate substantial speed improvement over conventional approaches, while retaining near-ideal hash value distribution. © 1997 ACM.