From 9b5a965efd128b85a70c3912498fe42c454899fe Mon Sep 17 00:00:00 2001
From: Mitsuru Kariya <kariya_mitsuru@hotmail.com>
Date: Sun, 29 Mar 2015 18:12:52 +0900
Subject: [PATCH] reduce includes' complexity on some inputs

cf. http://melpon.org/wandbox/permlink/mVNO3IDW8aawsRtD
---
 sprout/algorithm/includes.hpp | 45 ++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 17 deletions(-)

diff --git a/sprout/algorithm/includes.hpp b/sprout/algorithm/includes.hpp
index 7ed069eb..5d4f6524 100644
--- a/sprout/algorithm/includes.hpp
+++ b/sprout/algorithm/includes.hpp
@@ -19,24 +19,29 @@
 namespace sprout {
 	namespace detail {
 		template<typename RandomAccessIterator1, typename InputIterator2, typename Compare>
-		inline SPROUT_CONSTEXPR InputIterator2
+		inline SPROUT_CONSTEXPR sprout::pair<InputIterator2, bool>
 		includes_impl_ra(
-			RandomAccessIterator1 first1, RandomAccessIterator1 last1, InputIterator2 first2, InputIterator2 last2, Compare comp,
-			typename std::iterator_traits<RandomAccessIterator1>::difference_type pivot
+			RandomAccessIterator1 first1,
+			sprout::pair<InputIterator2, bool> current,
+			InputIterator2 last2, Compare comp,
+			typename std::iterator_traits<RandomAccessIterator1>::difference_type len
 			)
 		{
-			return first2 == last2 ? first2
-				: pivot == 0 ? (!comp(*first1, *first2) && !comp(*first2, *first1) ? sprout::next(first2) : first2)
+			typedef sprout::pair<InputIterator2, bool> type;
+			return current.second || current.first == last2 ? current
+				: len == 1 ? comp(*current.first, *first1)
+					? type(current.first, true)
+					: type(comp(*first1, *current.first) ? current.first : sprout::next(current.first), false)
 				: sprout::detail::includes_impl_ra(
-					sprout::next(first1, pivot), last1,
+					sprout::next(first1, len / 2),
 					sprout::detail::includes_impl_ra(
-						first1, sprout::next(first1, pivot),
-						first2,
+						first1,
+						current,
 						last2, comp,
-						pivot / 2
+						len / 2
 						),
 					last2, comp,
-					(sprout::distance(first1, last1) - pivot) / 2
+					len - len / 2
 					)
 				;
 		}
@@ -52,9 +57,11 @@ namespace sprout {
 		{
 			return first1 == last1 ? first2 == last2
 				: sprout::detail::includes_impl_ra(
-					first1, last1, first2, last2, comp,
-					sprout::distance(first1, last1) / 2
-					)
+					first1,
+					sprout::pair<InputIterator2, bool>(first2, false),
+					last2, comp,
+					sprout::distance(first1, last1)
+					).first
 					== last2
 				;
 		}
@@ -69,15 +76,19 @@ namespace sprout {
 		{
 			typedef sprout::pair<InputIterator1, InputIterator2> type;
 			return current.second == last2 || current.first == last1 ? current
-				: n == 1 ? !comp(*current.first, *current.second) && !comp(*current.second, *current.first)
-					? type(sprout::next(current.first), sprout::next(current.second))
-					: type(sprout::next(current.first), current.second)
+				: n == 1
+				? comp(*current.second, *current.first)
+					? type(last1, current.second)
+					: type(
+						sprout::next(current.first),
+						comp(*current.first, *current.second) ? current.second : sprout::next(current.second)
+						)
 				: sprout::detail::includes_impl_1(
 					sprout::detail::includes_impl_1(
 						current,
 						last1, last2, comp, n / 2
 						),
-					last1, last2, comp, n - n / 2
+					last1, last2, comp, n / 2
 					)
 				;
 		}