Definition of polyphase merge sort, possibly with links to more information and implementations. POLYPHASE MERGE SORTING — AN ADVANCED TECHNIQUE. R. L. Gilstad. Minneapolis-Honeywell Regulator Company. Electronic Data Processing. This article demonstrates one of the best known merge sorts, the polyphase merge. I make no sensational claims regarding the performance of this particular .
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Topological sorting Pre-topological order Pancake sorting Spaghetti sort.
Once all null runs are eliminated, however, the merge proceeds on an ideal basis. Sorting in memory is polyphase merge sort enough; when you have polyphase merge sort spill data into temporary files, you have a major organizational problem on your hands. I make no sensational claims regarding the performance of this particular version, although the polyphase algorithm seems to be generally recognized as highly efficient by most cognoscenti.
Class MergeList Listings 6 and 7 provides an interface to the template-based container library. This could be prohibitive for some applications. This polyphase merge sort fine, but I had to write separate iostream-based versions of fread and fwrite these appear on the ftp site.
If input data remains, the sort must generate a new sequence for the next level and continue until exhausting the source data. In contrast to internal sorting, an external merge sort can handle a data set of arbitrary size, usually but not necessarily too large to hold in memory at one time. Given N work files, the number of input files during a merge pass is N A number of merge sorting algorithms are presently known polyphase merge sort 1 ].
Polyphase merge sort – Wikipedia
Polyphawe after runs are constructed tapes will contain the data like in figure. You can also execute Sort polyphase merge sort any number of input files, one at a time, as long as the size polyphase merge sort the input data elements remains constant.
Dummy runs don’t need to occupy any space on the tapes, but the code has polyohase handle reaching the end of data on more than one tape during a phase on non-ideal distributions.
Again, I included no code to effect either solution. Tb1 and Tb2 contain group of runs. The code needs appropriate error polyphase merge sort exception handling, a primary requirement for real-world applications.
Polyphase merge sort
Some distribution algorithms include rearranging runs. AttachStream lets you attach a polyphase merge sort ffstream to a merge buffer for polyphase merge sort pre-sorting and distribution.
This initial phase pre-sorts each block internally, forming a sorted run, then writes it to metge of a number of work files. However, I view type security as a marginal issue in this case. Polyphase merge sort testing and debugging consumed much of the time needed to develop this sorting package. In contrast, all MergeFiles without null runs are added to the active list at the beginning of each mini-pass.
The problem is that since all the runs are on one tape, we must now put some of these runs on T2 to perform another merge. Also included are two iterator objects, one for each list. The appropriate input tape aort advanced, and if run on the mdrge tape is not yet completed, we insert the new element in priority queue.
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This is done polyphase merge sort extending basic 2-way merge to a k-way merge. The 4 ssort example shows a balanced 2-way merge sort. The current output file will become an input file for the next iteration.
So far, the package has been tested on input files ranging from one word, up to 3 million mergd “words” roughly 24 MB of fixed-length source data. Most discussions of sorting found in programming literature center on internal polyphase merge sort sorting. When this is done, we rewind all the tapes.
A polyphase merge sort is not a stable sort. Recall that after the completion of the distribution phase for N work files, at most N-1 of them contain sorted runs for input and the remaining output or target file polyphase merge sort initially empty.
First step is to read m records at a time from polylhase tape, sort them and write them alternatively to Tb1 and Tb2.
The sort has no control over the actual contents of polyphase merge sort source file submitted to it, templates or not. Suppose the data is initially on Ta1 and the internal memory can hold and sort m records at a time. The leftmost file at list mergr always contains the least number of runs.
polyphase merge sort |
Otherwise, it is necessary to pad the tape with dummy runs in order to get no. In that case, the merge routine simply decrements the null run count for that file and does not add it to the active list. Keeping track of run sizes can get complex, so a simple solution for tapes is to use a single file mark to indicate the end of a run and a double file mark to indicate the end of data. For everything to work out optimally, the last merge phase should have exactly one run on each input file.
What is the number of phases Assume run size is 1 element, 31 runs, 4 tapes. Here each succeeding level in the distribution matrix is skewed one place left for clarity. After initial distribution, run count: Member functions Get and Put extract and insert single items of buffered data. Once attached, a MergeFile won’t delete or modify the source file in polyphase merge sort way. Given R runs in the polyphase merge sort leftmost file, a polyphase merge sort pass for that level consists of merging R runs from each input file to the target file.
In general, polyphase merge sort is better than polyphase merge sort merge sort when there are less than 8 files, while ordinary merge sort starts to become better at around 8 or more files. Otherwise, in the more common case where the number of runs is not known in advance, “near optimal” distribution algorithms are used. Listings 8 and 9 present class PolySort, the high-level realization of the polysort algorithm.
All code presented here uses the default operator new.