/* SPDX-License-Identifier: AGPL-3.0-or-later */
/*
 * Soft:        The main goal of gtp-guard is to provide robust and secure
 *              extensions to GTP protocol (GPRS Tunneling Procol). GTP is
 *              widely used for data-plane in mobile core-network. gtp-guard
 *              implements a set of 3 main frameworks:
 *              A Proxy feature for data-plane tweaking, a Routing facility
 *              to inter-connect and a Firewall feature for filtering,
 *              rewriting and redirecting.
 *
 * Authors:     Alexandre Cassen, <acassen@gmail.com>
 *
 *              This program is free software; you can redistribute it and/or
 *              modify it under the terms of the GNU Affero General Public
 *              License Version 3.0 as published by the Free Software Foundation;
 *              either version 3.0 of the License, or (at your option) any later
 *              version.
 *
 * Copyright (C) 2023 Alexandre Cassen, <acassen@gmail.com>
 */

#include "list_head.h"

void list_sort(struct list_head *head,
	       int (*cmp)(struct list_head *a, struct list_head *b))
{
	struct list_head *p, *q, *e, *list, *tail, *oldhead;
	int insize, nmerges, psize, qsize, i;

	list = head->next;
	list_head_del(head);
	insize = 1;

	while (1) {
		p = oldhead = list;
		list = tail = NULL;
		nmerges = 0;

		while (p) {
			nmerges++;
			q = p;
			psize = 0;
			for (i = 0; i < insize; i++) {
				psize++;
				q = q->next == oldhead ? NULL : q->next;
				if (!q)
					break;
			}

			qsize = insize;
			while (psize > 0 || (qsize > 0 && q)) {
				if (!psize) {
					e = q;
					q = q->next;
					qsize--;
					if (q == oldhead)
						q = NULL;
				} else if (!qsize || !q) {
					e = p;
					p = p->next;
					psize--;
					if (p == oldhead)
						p = NULL;
				} else if (cmp(p, q) <= 0) {
					e = p;
					p = p->next;
					psize--;
					if (p == oldhead)
						p = NULL;
				} else {
					e = q;
					q = q->next;
					qsize--;
					if (q == oldhead)
						q = NULL;
				}
				if (tail)
					tail->next = e;
				else
					list = e;
				e->prev = tail;
				tail = e;
			}
			p = q;
		}

		tail->next = list;
		list->prev = tail;

		if (nmerges <= 1)
			break;

		insize *= 2;
	}

	head->next = list;
	head->prev = list->prev;
	list->prev->next = head;
	list->prev = head;
}
