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

llvm-svn: 228839

1 files changed, 35 insertions, 0 deletions

diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.min.max/minmax_init_list_comp.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.min.max/minmax_init_list_comp.pass.cpp
index 95a8c85c1da..beae3b60da0 100644
--- a/libcxx/test/std/algorithms/alg.sorting/alg.min.max/minmax_init_list_comp.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.sorting/alg.min.max/minmax_init_list_comp.pass.cpp
@@ -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)), "");