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    <p>std:sort is not exactly fast. </p> <p>Here are results I get comparing it to randomized parallel nonrecursive quicksort:</p> <p>pnrqSort (longs): .:.1 000 000 36ms (items per ms: 27777.8)</p> <p>.:.5 000 000 140ms (items per ms: 35714.3)</p> <p>.:.10 000 000 296ms (items per ms: 33783.8)</p> <p>.:.50 000 000 1s 484ms (items per ms: 33692.7)</p> <p>.:.100 000 000 2s 936ms (items per ms: 34059.9)</p> <p>.:.250 000 000 8s 300ms (items per ms: 30120.5)</p> <p>.:.400 000 000 12s 611ms (items per ms: 31718.3)</p> <p>.:.500 000 000 16s 428ms (items per ms: 30435.8)</p> <p>std::sort(longs) .:.1 000 000 134ms (items per ms: 7462.69)</p> <p>.:.5 000 000 716ms (items per ms: 6983.24)</p> <p>std::sort vector of longs</p> <p>1 000 000 511ms (items per ms: 1956.95)</p> <p>2 500 000 943ms (items per ms: 2651.11)</p> <p>Since you have extra method it is going to cause more stack use which will ultimately slow things down. Why median of 3 is used, I don't know, because it's a poor method, but with random pivot points quicksort never has big issues with uniform or presorted data and there's no danger of intentional median of 3 killer data.</p>
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    1. POHas anyone seen this improvement to quicksort before?
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    1. USCharles Eli Cheese
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    1. COYes, I've thought about using other pivot choosing methods including randomized pivots. That isn't the point. Also, notice that yours is both nonrecursive and parallel. Of course it will be faster! I used recursion because it is much simpler to implement and easier for people to quickly understand. My method can be made both nonrecursive and parallel as well. Yes, std::sort is not the fastest, but it provides a common function for comparison. The dual-pivot quicksort, however, is quite fast for being recursive and serial.
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      1. USJustin Peel
    2. COSo what is the point exactly? Apparently none, to downvote my response for no reason. Using two pivot methods will be twice the stack overhead, as I pointed out, and also as I pointed out it doesn't gain you anything over existing methods, so what's the point? Apparently none, just as with the question itself.
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      1. USCharles Eli Cheese
    3. COI downvoted your response because you were comparing apples to oranges. Comparing a nonrecursive, parallel quicksort with a recursive, serial quicksort is meaningless. You didn't even specify how many processors were being used. Using two different pivot methods does not double the number of stack calls - it is the same number of calls as using your basic quicksort. If you add the total number of stack calls to each function (qs1 and qs2) and to a basic quicksort you should get the same number. Also, maybe you missed that this can be used to improve nonrecursive and parallel methods.
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