From 951873098eeaab76186e55bf637e06f4b63fabfe Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Fri, 8 Dec 2023 22:45:55 +0200
Subject: [PATCH] BAN: Rewrite heap sort

Heap sort is now more close to gnulibc++ version. This is just more
simplified version.
---
 BAN/include/BAN/Sort.h | 122 +++++++++++++++++++++++++++++------------
 1 file changed, 86 insertions(+), 36 deletions(-)

diff --git a/BAN/include/BAN/Sort.h b/BAN/include/BAN/Sort.h
index e9a91e2eba..8182bf0fa1 100644
--- a/BAN/include/BAN/Sort.h
+++ b/BAN/include/BAN/Sort.h
@@ -44,7 +44,7 @@ namespace BAN::sort
 	template<typename It, typename Comp = less<typename It::value_type>>
 	void quick_sort(It begin, It end, Comp comp = {})
 	{
-		if (begin == end || next(begin, 1) == end)
+		if (distance(begin, end) <= 1)
 			return;
 		It mid = detail::partition(begin, end, comp);
 		quick_sort(begin, mid, comp);
@@ -54,7 +54,7 @@ namespace BAN::sort
 	template<typename It, typename Comp = less<typename It::value_type>>
 	void insertion_sort(It begin, It end, Comp comp = {})
 	{
-		if (begin == end || next(begin, 1) == end)
+		if (distance(begin, end) <= 1)
 			return;
 		for (It it1 = next(begin, 1); it1 != end; ++it1)
 		{
@@ -66,39 +66,87 @@ namespace BAN::sort
 		}
 	}
 
+	namespace detail
+	{
+
+		template<typename It, typename Comp>
+		void push_heap(It begin, size_t hole_index, size_t top_index, typename It::value_type value, Comp comp)
+		{
+			size_t parent = (hole_index - 1) / 2;
+			while (hole_index > top_index && comp(*next(begin, parent), value))
+			{
+				*next(begin, hole_index) = move(*next(begin, parent));
+				hole_index = parent;
+				parent = (hole_index - 1) / 2;
+			}
+			*next(begin, hole_index) = move(value);
+		}
+
+		template<typename It, typename Comp>
+		void adjust_heap(It begin, size_t hole_index, size_t len, typename It::value_type value, Comp comp)
+		{
+			const size_t top_index = hole_index;
+			size_t child = hole_index;
+			while (child < (len - 1) / 2)
+			{
+				child = 2 * (child + 1);
+				if (comp(*next(begin, child), *next(begin, child - 1)))
+					child--;
+				*next(begin, hole_index) = move(*next(begin, child));
+				hole_index = child;
+			}
+			if (len % 2 == 0 && child == (len - 2) / 2)
+			{
+				child = 2 * (child + 1);
+				*next(begin, hole_index) = move(*next(begin, child - 1));
+				hole_index = child - 1;
+			}
+			push_heap(begin, hole_index, top_index, move(value), comp);
+		}
+
+	}
+
+	template<typename It, typename Comp = less<typename It::value_type>>
+	void make_heap(It begin, It end, Comp comp = {})
+	{
+		const size_t len = distance(begin, end);
+		if (len <= 1)
+			return;
+
+		size_t parent = (len - 2) / 2;
+		while (true)
+		{
+			detail::adjust_heap(begin, parent, len, move(*next(begin, parent)), comp);
+
+			if (parent == 0)
+				break;
+			
+			parent--;
+		}
+	}
+
+	template<typename It, typename Comp = less<typename It::value_type>>
+	void sort_heap(It begin, It end, Comp comp = {})
+	{
+		const size_t len = distance(begin, end);
+		if (len <= 1)
+			return;
+
+		size_t last = len;
+		while (last > 1)
+		{
+			last--;
+			typename It::value_type x = move(*next(begin, last));
+			*next(begin, last) = move(*begin);
+			detail::adjust_heap(begin, 0, last, move(x), comp);
+		}
+	}
+
 	template<typename It, typename Comp = less<typename It::value_type>>
 	void heap_sort(It begin, It end, Comp comp = {})
 	{
-		if (begin == end || next(begin, 1) == end)
-			return;
-
-		It start = next(begin, distance(begin, end) / 2);
-
-		while (prev(end, 1) != begin)
-		{
-			if (start != begin)
-				--start;
-			else
-				swap(*(--end), *begin);
-
-			It root = start;
-			while (true)
-			{
-				size_t left_child = 2 * distance(begin, root) + 1;
-				if (left_child >= distance(begin, end))
-					break;
-
-				It child = next(begin, left_child);
-				if (next(child, 1) != end && comp(*child, *next(child, 1)))
-					++child;
-
-				if (!comp(*root, *child))
-					break;
-
-				swap(*root, *child);
-				root = child;
-			}
-		}
+		make_heap(begin, end, comp);
+		sort_heap(begin, end, comp);
 	}
 
 	namespace detail
@@ -107,7 +155,7 @@ namespace BAN::sort
 		template<typename It, typename Comp>
 		void intro_sort_impl(It begin, It end, size_t max_depth, Comp comp)
 		{
-			if (distance(begin, end) < 16)
+			if (distance(begin, end) <= 16)
 				return insertion_sort(begin, end, comp);
 			if (max_depth == 0)
 				return heap_sort(begin, end, comp);
@@ -121,14 +169,16 @@ namespace BAN::sort
 	template<typename It, typename Comp = less<typename It::value_type>>
 	void intro_sort(It begin, It end, Comp comp = {})
 	{
-		size_t max_depth = Math::ilog2(distance(begin, end));
-		detail::intro_sort_impl(begin, end, max_depth, comp);
+		const size_t len = distance(begin, end);
+		if (len <= 1)
+			return;
+		detail::intro_sort_impl(begin, end, 2 * Math::ilog2(len), comp);
 	}
 
 	template<typename It, typename Comp = less<typename It::value_type>>
 	void sort(It begin, It end, Comp comp = {})
 	{
-		return sort::intro_sort(begin, end, comp);
+		return intro_sort(begin, end, comp);
 	}
 
 }