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/**
@file     hashtable_compat.h
@brief    Support hashtable for kernel <= 3.6
@details  Copyright (c) 2023 Acronis International GmbH
@author   Bruce Wang (bruce.wang@acronis.com)
@since    $Id: $
*/
#pragma once

#include <linux/list.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/hash.h>
#include <linux/rculist.h>

#ifdef HAVE_HASHTABLE_H
#include <linux/hashtable.h>
#else

#define DECLARE_HASHTABLE(name, bits) \
	struct hlist_head name[1 << (bits)]

static inline void __hash_init(struct hlist_head *ht, unsigned int sz)
{
	unsigned int i;

	for (i = 0; i < sz; i++)
		INIT_HLIST_HEAD(&ht[i]);
}
#define hash_init(hashtable) __hash_init(hashtable, ARRAY_SIZE(hashtable))

static inline void hash_del_rcu(struct hlist_node *node)
{
	hlist_del_init_rcu(node);
}

#endif

#ifndef hlist_entry_safe
#define hlist_entry_safe(ptr, type, member)                  \
	({                                                       \
		typeof(ptr) ____ptr = (ptr);                         \
		____ptr ? hlist_entry(____ptr, type, member) : NULL; \
	})
#endif

#ifndef hlist_first_rcu
#define hlist_first_rcu(head)	(*((struct hlist_node __rcu **)(&(head)->first)))
#endif

#ifndef hlist_next_rcu
#define hlist_next_rcu(node)	(*((struct hlist_node __rcu **)(&(node)->next)))
#endif


#undef hlist_for_each_entry
#define hlist_for_each_entry(pos, head, member)                         \
	for (pos = hlist_entry_safe((head)->first, typeof(*(pos)), member); \
		 pos;                                                           \
		 pos = hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))

#undef hlist_for_each_entry_rcu
#define hlist_for_each_entry_rcu(pos, head, member)                         \
	for (pos = hlist_entry_safe(rcu_dereference(hlist_first_rcu(head)), \
								typeof(*(pos)), member);                    \
		 pos;                                                               \
		 pos = hlist_entry_safe(rcu_dereference(hlist_next_rcu(         \
									&(pos)->member)),                       \
								typeof(*(pos)), member))						

static inline uint64_t moremur(uint64_t x) {
  x ^= x >> 27;
  x *= 0x3C79AC492BA7B653UL;
  x ^= x >> 33;
  x *= 0x1C69B3F74AC4AE35UL;
  x ^= x >> 27;

  return x;
}

static inline uint64_t moremur_hash(uint64_t val, unsigned int bits)
{
  return moremur(val) >> (64 - bits);
}

#define hash_add_rcu_hashbits(hashtable, node, key, hashbits) \
	hlist_add_head_rcu(node, &hashtable[moremur_hash(key, hashbits)])

#define hash_for_each_possible_with_hashbits(name, obj, member, key, hashbits) \
	hlist_for_each_entry(obj, &name[moremur_hash(key, hashbits)], member)

#define hash_for_each_possible_rcu_with_hashbits(name, obj, member, key, hashbits) \
	hlist_for_each_entry_rcu(obj, &name[moremur_hash(key, hashbits)], member)