mariadb/storage/innobase/include/hash0hash.h

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/**************************************************//**
@file include/hash0hash.h
The simple hash table utility

Created 5/20/1997 Heikki Tuuri
*******************************************************/

#pragma once
#include "ut0rnd.h"
#include "ut0new.h"

struct hash_cell_t
{
  /** singly-linked, nullptr terminated list of hash buckets */
  void *node;

private:
  /** @return pointer to the first element
  @tparam T      type of the element */
  template<typename T> T **begin() noexcept
  { return reinterpret_cast<T**>(&node); }
  /** @return pointer to the last element
  @tparam T      type of the element
  @param next    the next-element pointer in T */
  template<typename T> T **end(T *T::*next) noexcept
  {
    T **prev;
    for (prev= begin<T>(); *prev; prev= &((*prev)->*next));
    return prev;
  }

public:
  /** Append an element.
  @tparam T      type of the element
  @param insert  the being-inserted element
  @param next    the next-element pointer in T */
  template<typename T>
  void append(T &insert, T *T::*next) noexcept
  {
    insert.*next= nullptr;
    *end<T>(next)= &insert;
  }

  /** Find for an element.
  @tparam T          type of the element
  @tparam UnaryPred  unary predicate
  @param next        the next-element pointer in T
  @param u           unary predicate for searching the element
  @return the first matching element
  @retval nullptr if not found */
  template<typename T,typename UnaryPred>
  T *find(T *T::*next, UnaryPred u) const noexcept
  {
    T *n;
    for (n= static_cast<T*>(node); n && !u(n); n= n->*next);
    return n;
  }

  /** Search for a pointer to an element.
  @tparam T          type of the element
  @tparam UnaryPred  unary predicate
  @param next        the next-element pointer in T
  @param u           unary predicate for searching the element
  @return pointer to the first matching element,
  or to the last element in the chain */
  template<typename T,typename UnaryPred>
  T **search(T *T::*next, UnaryPred u) noexcept
  {
    T **prev;
    for (prev= begin<T>(); !u(*prev); prev= &((*prev)->*next));
    return prev;
  }

  /** Remove an element.
  @tparam T          type of the element
  @param prev        pointer to the element to be removed
  @param next        the next-element pointer in T */
  template<typename T>
  void remove(T **prev, T *T::*next) noexcept
  {
    T &element= **prev;
    *prev= element.*next;
    element.*next= nullptr;
  }

  /** Remove an element.
  @tparam T      type of the element
  @param element the being-removed element
  @param next    the next-element pointer in T */
  template<typename T>
  void remove(T &element, T *T::*next) noexcept
  {
    remove(search(next, [&element](const T *p){return p==&element;}), next);
  }
};

/** Hash table with singly-linked overflow lists */
struct hash_table_t
{
  /** number of elements in array (a prime number) */
  ulint n_cells;
  /** the hash array */
  hash_cell_t *array;

  /** Create the hash table.
  @param n  the lower bound of n_cells */
  void create(ulint n) noexcept
  {
    n_cells= ut_find_prime(n);
    array= static_cast<hash_cell_t*>(ut_zalloc_nokey(n_cells * sizeof *array));
  }

  /** Clear the hash table. */
  void clear() noexcept { memset(array, 0, n_cells * sizeof *array); }

  /** Free the hash table. */
  void free() noexcept { ut_free(array); array= nullptr; }

  ulint calc_hash(ulint fold) const noexcept { return fold % n_cells; }

  hash_cell_t *cell_get(ulint fold) const noexcept
  { return &array[calc_hash(fold)]; }
};