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Quick sort: Replace recursion with custom stack, small improvements #84

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Quick sort: Replace recursion with custom stack, small improvements #84

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Commits on Dec 12, 2022

  1. Quick sort: Replace recursion with custom stack, small improvements 

    Instead of recursing just roll a custom stack with low/high bounds
of the next region.

Also tune some of the logic a bit.
    - Simpler (and faster) median + setup for partition
    - Remove some unnecessary branches in hot control flow.

Results in roughly 10% perf improvement on the project benchmarks:
(See PR for full run data)

4027959.8 / 4258144.7 -> 0.9459
Quick_sort 100000 x86_64                  249        4027959.8 ns/op
Quick_sort 100000 x86_64                  235        4258144.7 ns/op

Running tests with random numbers: 902582.0 / 940650.0 -> 0.9595
sort.h quick_sort             - ok,   902582.0 usec
sort.h quick_sort             - ok,   940650.0 usec

Running tests with same number: 8986.0 / 9059.0 -> 0.9919
sort.h quick_sort             - ok,     8986.0 usec
sort.h quick_sort             - ok,     9059.0 usec

Running tests with sorted numbers: 148790.0 / 160015.0 -> 0.9299
sort.h quick_sort             - ok,   148790.0 usec
sort.h quick_sort             - ok,   160015.0 usec

Running tests with sorted blocks of length 10: 872430.0 / 915431.0 -> 0.953
sort.h quick_sort             - ok,   872430.0 usec
sort.h quick_sort             - ok,   915431.0 usec

Running tests with sorted blocks of length 100: 751763.0 / 791987.0 -> 0.9492
sort.h quick_sort             - ok,   751763.0 usec
sort.h quick_sort             - ok,   791987.0 usec

Running tests with sorted blocks of length 10000: 461118.0 / 514853.0 -> 0.8956
sort.h quick_sort             - ok,   461118.0 usec
sort.h quick_sort             - ok,   514853.0 usec

Running tests with swapped size/2 pairs: 812161.0 / 854230.0 -> 0.9508
sort.h quick_sort             - ok,   812161.0 usec
sort.h quick_sort             - ok,   854230.0 usec

Running tests with swapped size/8 pairs: 522638.0 / 575848.0 -> 0.9076
sort.h quick_sort             - ok,   522638.0 usec
sort.h quick_sort             - ok,   575848.0 usec

Running tests with known evil data: 146601.0 / 196450.0 -> 0.7463
sort.h quick_sort             - ok,   146601.0 usec
sort.h quick_sort             - ok,   196450.0 usec

So roughly a 5-10% for most cases with the outliers being no-change
for same-number and 25% improvement for "evil data".
    @goldsteinn
    goldsteinn committed Dec 12, 2022
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