Reuse and optimize sorting logic for List, SelfList, and HashMap

Added SortList class, and updated List, SelfList, and HashMap sort methods to use it.  Sorting is done with merge sort, with an initial check to optimize for already sorted lists, and sorted lists that were appended to.

Author: aaronp64

core/templates/hash_map.h

@@ -33,6 +33,7 @@
 #include "core/os/memory.h"
 #include "core/templates/hashfuncs.h"
 #include "core/templates/pair.h"
+#include "core/templates/sort_list.h"
 
 #include <initializer_list>
 
@@ -60,8 +61,6 @@ struct HashMapElement {
 			data(p_key, p_value) {}
 };
 
-bool _hashmap_variant_less_than(const Variant &p_left, const Variant &p_right);
-
 template <typename TKey, typename TValue,
 		typename Hasher = HashMapHasherDefault,
 		typename Comparator = HashMapComparatorDefault<TKey>,
@@ -265,44 +264,18 @@ class HashMap : private Allocator {
 	}
 
 	void sort() {
-		if (elements == nullptr || num_elements < 2) {
-			return; // An empty or single element HashMap is already sorted.
-		}
-		// Use insertion sort because we want this operation to be fast for the
-		// common case where the input is already sorted or nearly sorted.
-		HashMapElement<TKey, TValue> *inserting = head_element->next;
-		while (inserting != nullptr) {
-			HashMapElement<TKey, TValue> *after = nullptr;
-			for (HashMapElement<TKey, TValue> *current = inserting->prev; current != nullptr; current = current->prev) {
-				if (_hashmap_variant_less_than(inserting->data.key, current->data.key)) {
-					after = current;
-				} else {
-					break;
-				}
-			}
-			HashMapElement<TKey, TValue> *next = inserting->next;
-			if (after != nullptr) {
-				// Modify the elements around `inserting` to remove it from its current position.
-				inserting->prev->next = next;
-				if (next == nullptr) {
-					tail_element = inserting->prev;
-				} else {
-					next->prev = inserting->prev;
-				}
-				// Modify `before` and `after` to insert `inserting` between them.
-				HashMapElement<TKey, TValue> *before = after->prev;
-				if (before == nullptr) {
-					head_element = inserting;
-				} else {
-					before->next = inserting;
-				}
-				after->prev = inserting;
-				// Point `inserting` to its new surroundings.
-				inserting->prev = before;
-				inserting->next = after;
-			}
-			inserting = next;
+		sort_custom<KeyValueSort<TKey, TValue>>();
+	}
+
+	template <typename C>
+	void sort_custom() {
+		if (size() < 2) {
+			return;
 		}
+
+		using E = HashMapElement<TKey, TValue>;
+		SortList<E, KeyValue<TKey, TValue>, &E::data, &E::prev, &E::next, C> sorter;
+		sorter.sort(head_element, tail_element);
 	}
 
 	TValue &get(const TKey &p_key) {

core/templates/list.h

@@ -32,7 +32,7 @@
 
 #include "core/error/error_macros.h"
 #include "core/os/memory.h"
-#include "core/templates/sort_array.h"
+#include "core/templates/sort_list.h"
 
 #include <initializer_list>
 
@@ -656,104 +656,18 @@ class List {
 		where->prev_ptr = value;
 	}
 
-	/**
-	 * simple insertion sort
-	 */
-
 	void sort() {
 		sort_custom<Comparator<T>>();
 	}
 
-	template <typename C>
-	void sort_custom_inplace() {
-		if (size() < 2) {
-			return;
-		}
-
-		Element *from = front();
-		Element *current = from;
-		Element *to = from;
-
-		while (current) {
-			Element *next = current->next_ptr;
-
-			if (from != current) {
-				current->prev_ptr = nullptr;
-				current->next_ptr = from;
-
-				Element *find = from;
-				C less;
-				while (find && less(find->value, current->value)) {
-					current->prev_ptr = find;
-					current->next_ptr = find->next_ptr;
-					find = find->next_ptr;
-				}
-
-				if (current->prev_ptr) {
-					current->prev_ptr->next_ptr = current;
-				} else {
-					from = current;
-				}
-
-				if (current->next_ptr) {
-					current->next_ptr->prev_ptr = current;
-				} else {
-					to = current;
-				}
-			} else {
-				current->prev_ptr = nullptr;
-				current->next_ptr = nullptr;
-			}
-
-			current = next;
-		}
-		_data->first = from;
-		_data->last = to;
-	}
-
-	template <typename C>
-	struct AuxiliaryComparator {
-		C compare;
-		_FORCE_INLINE_ bool operator()(const Element *a, const Element *b) const {
-			return compare(a->value, b->value);
-		}
-	};
-
 	template <typename C>
 	void sort_custom() {
-		//this version uses auxiliary memory for speed.
-		//if you don't want to use auxiliary memory, use the in_place version
-
-		int s = size();
-		if (s < 2) {
+		if (size() < 2) {
 			return;
 		}
 
-		Element **aux_buffer = memnew_arr(Element *, s);
-
-		int idx = 0;
-		for (Element *E = front(); E; E = E->next_ptr) {
-			aux_buffer[idx] = E;
-			idx++;
-		}
-
-		SortArray<Element *, AuxiliaryComparator<C>> sort;
-		sort.sort(aux_buffer, s);
-
-		_data->first = aux_buffer[0];
-		aux_buffer[0]->prev_ptr = nullptr;
-		aux_buffer[0]->next_ptr = aux_buffer[1];
-
-		_data->last = aux_buffer[s - 1];
-		aux_buffer[s - 1]->prev_ptr = aux_buffer[s - 2];
-		aux_buffer[s - 1]->next_ptr = nullptr;
-
-		for (int i = 1; i < s - 1; i++) {
-			aux_buffer[i]->prev_ptr = aux_buffer[i - 1];
-			aux_buffer[i]->next_ptr = aux_buffer[i + 1];
-		}
-
-		memdelete_arr(aux_buffer);
+		SortList<Element, T, &Element::value, &Element::prev_ptr, &Element::next_ptr, C> sorter;
+		sorter.sort(_data->first, _data->last);
 	}
 
 	const void *id() const {

core/templates/self_list.h

@@ -31,6 +31,7 @@
 #pragma once
 
 #include "core/error/error_macros.h"
+#include "core/templates/sort_list.h"
 #include "core/typedefs.h"
 
 template <typename T>
@@ -114,45 +115,13 @@ class SelfList {
 				return;
 			}
 
-			SelfList<T> *from = _first;
-			SelfList<T> *current = from;
-			SelfList<T> *to = from;
-
-			while (current) {
-				SelfList<T> *next = current->_next;
-
-				if (from != current) {
-					current->_prev = nullptr;
-					current->_next = from;
-
-					SelfList<T> *find = from;
-					C less;
-					while (find && less(*find->_self, *current->_self)) {
-						current->_prev = find;
-						current->_next = find->_next;
-						find = find->_next;
-					}
-
-					if (current->_prev) {
-						current->_prev->_next = current;
-					} else {
-						from = current;
-					}
-
-					if (current->_next) {
-						current->_next->_prev = current;
-					} else {
-						to = current;
-					}
-				} else {
-					current->_prev = nullptr;
-					current->_next = nullptr;
-				}
-
-				current = next;
-			}
-			_first = from;
-			_last = to;
+			struct PtrComparator {
+				C compare;
+				_FORCE_INLINE_ bool operator()(const T *p_a, const T *p_b) const { return compare(*p_a, *p_b); }
+			};
+			using Element = SelfList<T>;
+			SortList<Element, T *, &Element::_self, &Element::_prev, &Element::_next, PtrComparator> sorter;
+			sorter.sort(_first, _last);
 		}
 
 		_FORCE_INLINE_ SelfList<T> *first() { return _first; }

core/templates/sort_list.h

@@ -0,0 +1,148 @@
+/**************************************************************************/
+/*  sort_list.h                                                           */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#pragma once
+
+#include "core/typedefs.h"
+
+template <typename Element, typename T, T Element::*value, Element *Element::*prev, Element *Element::*next, typename Comparator = Comparator<T>>
+class SortList {
+public:
+	Comparator compare;
+
+	void sort(Element *&r_head, Element *&r_tail) {
+		Element *sorted_until;
+		if (_is_sorted(r_head, r_tail, sorted_until)) {
+			return;
+		}
+
+		// In case we're sorting only part of a larger list.
+		Element *head_prev = r_head->*prev;
+		r_head->*prev = nullptr;
+		Element *tail_next = r_tail->*next;
+		r_tail->*next = nullptr;
+
+		// Sort unsorted section and merge.
+		Element *head2 = sorted_until->*next;
+		_split(sorted_until, head2);
+		_merge_sort(head2, r_tail);
+		_merge(r_head, sorted_until, head2, r_tail, r_head, r_tail);
+
+		// Reconnect to larger list if needed.
+		if (head_prev) {
+			_connect(head_prev, r_head);
+		}
+		if (tail_next) {
+			_connect(r_tail, tail_next);
+		}
+	}
+
+private:
+	bool _is_sorted(Element *p_head, Element *p_tail, Element *&r_sorted_until) {
+		r_sorted_until = p_head;
+		while (r_sorted_until != p_tail) {
+			if (compare(r_sorted_until->*next->*value, r_sorted_until->*value)) {
+				return false;
+			}
+
+			r_sorted_until = r_sorted_until->*next;
+		}
+
+		return true;
+	}
+
+	void _merge_sort(Element *&r_head, Element *&r_tail) {
+		if (r_head == r_tail) {
+			return;
+		}
+
+		Element *tail1 = _get_mid(r_head);
+		Element *head2 = tail1->*next;
+		_split(tail1, head2);
+
+		_merge_sort(r_head, tail1);
+		_merge_sort(head2, r_tail);
+		_merge(r_head, tail1, head2, r_tail, r_head, r_tail);
+	}
+
+	void _merge(
+			Element *p_head1, Element *p_tail1,
+			Element *p_head2, Element *p_tail2,
+			Element *&r_head, Element *&r_tail) {
+		if (compare(p_head2->*value, p_head1->*value)) {
+			r_head = p_head2;
+			p_head2 = p_head2->*next;
+		} else {
+			r_head = p_head1;
+			p_head1 = p_head1->*next;
+		}
+
+		Element *curr = r_head;
+		while (p_head1 && p_head2) {
+			if (compare(p_head2->*value, p_head1->*value)) {
+				_connect(curr, p_head2);
+				p_head2 = p_head2->*next;
+			} else {
+				_connect(curr, p_head1);
+				p_head1 = p_head1->*next;
+			}
+			curr = curr->*next;
+		}
+
+		if (p_head1) {
+			_connect(curr, p_head1);
+			r_tail = p_tail1;
+		} else {
+			_connect(curr, p_head2);
+			r_tail = p_tail2;
+		}
+	}
+
+	Element *_get_mid(Element *p_head) {
+		Element *end = p_head;
+		Element *mid = p_head;
+		while (end->*next && end->*next->*next) {
+			end = end->*next->*next;
+			mid = mid->*next;
+		}
+
+		return mid;
+	}
+
+	_FORCE_INLINE_ void _connect(Element *p_a, Element *p_b) {
+		p_a->*next = p_b;
+		p_b->*prev = p_a;
+	}
+
+	_FORCE_INLINE_ void _split(Element *p_a, Element *p_b) {
+		p_a->*next = nullptr;
+		p_b->*prev = nullptr;
+	}
+};