http://llvm.org/bugs/show_bug.cgi?id=22427
Bug ID: 22427
Summary: inplace_merge should not apply more than (last -
first) - 1 comparisons if enough additional memory is
available
Product: libc++
Version: unspecified
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
Created attachment 13787
--> http://llvm.org/bugs/attachment.cgi?id=13787&action=edit
clang++ -v
Please see the sample code below.
================================= sample code =================================
#include <algorithm>
#include <iostream>
#include <vector>
int main()
{
std::vector<int> v = { 1, 3, 5, 2, 4, 6 };
int count = 0;
std::inplace_merge(v.begin(), v.end() - 3, v.end(),
[&count](int lhs, int rhs) -> bool { ++count; return lhs < rhs; });
std::for_each(v.begin(), v.end(), [](int x) { std::cout << x << ", "; });
std::cout << std::endl << count << " comparisons" << std::endl;
}
================================= sample code =================================
================================= output =================================
1, 2, 3, 4, 5, 6,
8 comparisons
================================= output =================================
cf. http://melpon.org/wandbox/permlink/u0NiYiwQ1fNUk7je
The C++11 standard 25.4.4[alg.merge]/p.8 says, "When enough additional memory
is available, (last - first) - 1 comparisons."
I believe that enough additional memory is available in the sample code above,
so it should apply at most 5 comparisons.
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