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Improving quicksort performance with a codeword data structure

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2 Author(s)
J. -L. Baer ; Dept. of Comput. Sci., Washington Univ., Seattle, WA, USA ; Y. -B. Lin
Cited in Patents(3) Patent Links Provided by 1790 Analytics
  1. Callaghan, Mark D. ;  Li, Wei Z. ;  Waddington, William H. ,  "METHOD FOR SORTING DATA USING COMMON PREFIX BYTES" , Patent No. 7680791 More
    Callaghan, Mark D. ; Li, Wei Z. ; Waddington, William H.

    Several techniques for sorting item are described, generally referred to as (1) common prefix skipping quicksort; (2) key substring caching; and (3) adaptive quicksort. With common prefix skipping quicksort, common prefix bytes among all key values for a partition are computed while performing a quicksort partitioning operation, and the known common bytes are skipped when comparing two key values in a recursive partitioning operation. With key substring caching, each item is represented in a cached array comprising a particular number of bytes for respective portions of key values ("key substring"), where the key substring cache is updated contain bytes beyond the known number of common prefix bytes. An adaptive quicksort routine is a hybrid of a quicksort function and most significant digit radix sort function, where the functions are mutually recursive. </p>

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  2. Callaghan, Mark D. ;  Potapov, Dmitry M. ,  "ENCODING DATA TO BE SORTED" , Patent No. 7587396 More
    Callaghan, Mark D. ; Potapov, Dmitry M.

    Key conditioning involves the construction of a byte orderable array from values for a possibly multi-field key concatenated key, for comparison by a sort routine. Byte-orderable sort keys are conditioned prior to execution of a sort routine, to facilitate an accurate and/or efficient sort procedure. For example, key conditioning may be applied to values in one or more columns of a database table, where the column(s) are used as keys for sorting rows of the table. Six factors are considered in encoding the byte array, such as whether nulls compare high or low; whether a field is fixed width or variable width; whether a field is guaranteed to be not null; whether a field is ordered ascending or descending; whether a field is the last field of a multi-field sort key or the only field of a sort key; and whether a field is likely to contain a significant number of zero values. </p>

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  3. Arnold, William D. ,  "BALANCED AND STABILIZED QUICKSORT METHOD" , Patent No. 5535378 More
    Arnold, William D.

    The improved Quicksort method of the present invention utilizes two pointers initialized at opposite ends of the array or partition to be sorted and an initial partition value Pvalue located at the center of the array or partition. The value at each of the end pointers is then compared to Pvalue. Sorting is accomplished by recursing the partition process for the two array segments bounded on one side by the final P valve location. This method prevents excessive recursions, and allows the identical array case to recurse to the ideal minimum: Log2(N). Also, by relaxing the offsider criteria to include elements equal to Pvalue, the present invention presents arrays of two valves or a very small range of valves from recursing excessively. Further, the sorting method of the present invention may test the final position of the initial Pvalue to determine whether it is in the center (75%?95%) portion of the array or subarray being positioned. If it is not, the first Pvalue is disregarded, and a new initial Pvalue is selected, preferably randomly selected from the larger subarray bounded on one side by the final Pvalue location resulting from the initial attempt. This method prevents arrays situated in "pipe organ" sequence from recursing excessively. In addition, a maximum recursion depth limit may be specified to force section of a new initial Pvalue if a recursion level exceeds the depth limit.

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