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Fix PR 22541: When values are equal, minmax should return the rightmost one in the initializer_list 

llvm-svn: 228839
This commit is contained in:
Marshall Clow 2015-02-11 15:41:34 +00:00
parent 8a8b00b684
commit 002144f61d
2 changed files with 41 additions and 6 deletions
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12
libcxx/include/algorithm
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@ -2771,7 +2771,7 @@ minmax(initializer_list<_Tp> __t, _Compare __comp)
typedef typename initializer_list<_Tp>::const_iterator _Iter;
_Iter __first = __t.begin();
_Iter __last = __t.end();
std::pair<_Tp, _Tp> __result ( *__first, *__first );
std::pair<_Tp, _Tp> __result(*__first, *__first);
++__first;
if (__t.size() % 2 == 0)
@ -2786,13 +2786,13 @@ minmax(initializer_list<_Tp> __t, _Compare __comp)
while (__first != __last)
{
_Tp __prev = *__first++;
if (__comp(__prev, *__first)) {
if (__comp(__prev, __result.first)) __result.first = __prev;
if (__comp(__result.second, *__first)) __result.second = *__first;
if (__comp(*__first, __prev)) {
if ( __comp(*__first, __result.first)) __result.first = *__first;
if (!__comp(__prev, __result.second)) __result.second = __prev;
}
else {
if (__comp(*__first, __result.first)) __result.first = *__first;
if (__comp(__result.second, __prev)) __result.second = __prev;
if ( __comp(__prev, __result.first)) __result.first = __prev;
if (!__comp(*__first, __result.second)) __result.second = *__first;
}
__first++;

35
libcxx/test/std/algorithms/alg.sorting/alg.min.max/minmax_init_list_comp.pass.cpp
View File

@ -12,11 +12,27 @@
// template<class T, class Compare>
// pair<T, T>
// minmax(initializer_list<T> t, Compare comp);
//
// Complexity: At most (3/2) * t.size() applications of the corresponding predicate.
#include <algorithm>
#include <functional>
#include <cassert>
#include "counting_predicates.hpp"
bool all_equal(int a, int b) { return false; } // everything is equal
void test_all_equal(std::initializer_list<int> il)
{
binary_counting_predicate<bool(*)(int, int), int, int> pred (all_equal);
std::pair<int, int> p = std::minmax(il, std::ref(pred));
const int *ptr = il.end();
assert(p.first == *il.begin());
assert(p.second == *--ptr);
assert(pred.count() <= ((3 * il.size()) / 2));
}
int main()
{
#ifndef _LIBCPP_HAS_NO_GENERALIZED_INITIALIZERS
@ -26,6 +42,25 @@ int main()
assert((std::minmax({2, 3, 1}, std::greater<int>()) == std::pair<int, int>(3, 1)));
assert((std::minmax({3, 1, 2}, std::greater<int>()) == std::pair<int, int>(3, 1)));
assert((std::minmax({3, 2, 1}, std::greater<int>()) == std::pair<int, int>(3, 1)));
assert((std::minmax({1, 2, 3}, all_equal ) == std::pair<int, int>(1, 3)));
binary_counting_predicate<std::greater<int>, int, int> pred ((std::greater<int>()));
assert((std::minmax({1, 2, 2, 3, 3, 3, 5, 5, 5, 5, 5, 3}, std::ref(pred)) == std::pair<int, int>(5, 1)));
assert(pred.count() <= 18); // size == 12
test_all_equal({0});
test_all_equal({0,1});
test_all_equal({0,1,2});
test_all_equal({0,1,2,3});
test_all_equal({0,1,2,3,4});
test_all_equal({0,1,2,3,4,5});
test_all_equal({0,1,2,3,4,5,6});
test_all_equal({0,1,2,3,4,5,6,7});
test_all_equal({0,1,2,3,4,5,6,7,8});
test_all_equal({0,1,2,3,4,5,6,7,8,9});
test_all_equal({0,1,2,3,4,5,6,7,8,9,10});
test_all_equal({0,1,2,3,4,5,6,7,8,9,10,11});
#if _LIBCPP_STD_VER > 11
{
static_assert((std::minmax({1, 2, 3}, std::greater<int>()) == std::pair<int, int>(3, 1)), "");