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bitsetsort fix reverse_conditional_swap

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This commit is contained in:
Maksim Kita 2022-02-02 12:44:04 +00:00
parent f301e50b23
commit c39ad2aa49
1 changed files with 71 additions and 1 deletions
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72
base/base/BitSetSort.h
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@ -84,7 +84,77 @@ class __reverse_conditional_swap {
*__y = __result ? _VSTD::move(*__y) : _VSTD::move(*__x);
*__x = _VSTD::move(__min);
} else {
if (__result) {
/** This change is required for ClickHouse.
* It seems that this is slow branch, and its logic should be identical to fast branch.
* Logic of fast branch,
* if (result)
* min = x;
* y = y;
* x = x;
* else
* min = y;
* y = x;
* x = y;
*
* We swap elements only if result is false.
*
* Example to reproduce sort bug:
* int main(int argc, char ** argv)
* {
* (void)(argc);
* (void)(argv);
*
* std::vector<std::pair<Int64, Int64>> values = {
* {1, 1},
* {3, -1},
* {2, 1},
* {7, -1},
* {3, 1},
* {999, -1},
* {4, 1},
* {7, -1},
* {5, 1},
* {8, -1}
* };
*
* ::stdext::bitsetsort(values.begin(), values.end());
* bool is_sorted = std::is_sorted(values.begin(), values.end());
*
* std::cout << "Array " << values.size() << " is sorted " << is_sorted << std::endl;
*
* for (auto & value : values)
* std::cout << value.first << " " << value.second << std::endl;
*
* return 0;
* }
*
* Output before change:
* Array 10 is sorted 0
* 1 1
* 2 1
* 3 -1
* 3 1
* 4 1
* 7 -1
* 7 -1
* 8 -1
* 5 1
* 999 -1
*
* After change:
* Array 10 is sorted 1
* 1 1
* 2 1
* 3 -1
* 3 1
* 4 1
* 5 1
* 7 -1
* 7 -1
* 8 -1
* 999 -1
*/
if (!__result) {
_VSTD::iter_swap(__x, __y);
}
}