Improving quicksort performance with a codeword data structure

Abstract
The problem is discussed of how the use of a new data structure, the codeword structure, can help improve the performance of quicksort when the records to be sorted are long and the keys are alphanumeric sequences of bytes. The codeword is a compact representation of a key with respect to some codeword generator. It consists of a byte for a character count of equal bytes, a byte for the first nonequal byte, and a pointer to the record. It is shown how the ordering of keys is preserved by an adequate choice of the code generator and how this can be applied to the quicksort algorithm. An analysis of the potential saving son various architectures and actual measurements shows the improvements that can be attained by using codewords rather than pointers. Architecturally independent parameters, such as the number of bytes to be compared, the number of swaps, architecture-dependent parameters such as caches and their write policies, and compiler optimizations such as in-line expansion and register allocation are considered.

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