hashFunc.h

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#ifndef GUM_HASH_FUNC_H
#define GUM_HASH_FUNC_H

// utility provides the std::pair <> template
#include <climits>
#include <string>
#include <type_traits>
#include <utility>

#include <agrum/agrum.h>
#include <agrum/tools/core/refPtr.h>

namespace gum {

  unsigned int __hashTableLog2(const Size nb);

  struct HashFuncConst {
    static constexpr Size gold =
       sizeof(Size) == 4 ? Size(2654435769UL) : Size(11400714819323198486UL);
    static constexpr Size pi =
       sizeof(Size) == 4 ? Size(3373259426UL) : Size(14488038916154245684UL);
    static constexpr Size mask =
       sizeof(Size) == 4 ? Size(4294967295UL) : Size(18446744073709551615UL);
    static constexpr Size offset = sizeof(Size) == 4 ? Size(32) : Size(64);
  };


  // ===========================================================================
  // ===             BASE CLASS SHARED BY ALL THE HASH FUNCTIONS             ===
  // ===========================================================================
  template < typename Key >
  class HashFuncBase {
    public:
    void resize(const Size new_size);

    Size size() const;

    virtual Size operator()(const Key& key) const = 0;

    protected:
    Size _hash_size{Size(0)};

    unsigned int _hash_log2_size{0};

    Size _hash_mask{Size(0)};

    unsigned int _right_shift{0};
  };


  // ===========================================================================
  // ===                GENERIC HASH FUNCTIONS FOR SIMPLE TYPES              ===
  // ===========================================================================

  template < typename Key >
  class HashFuncSmallKey: public HashFuncBase< Key > {
    public:
    HashFuncSmallKey();

    static Size castToSize(const Key& key);

    virtual Size operator()(const Key& key) const override final;
  };


  template < typename Key >
  class HashFuncSmallCastKey: public HashFuncBase< Key > {
    public:
    HashFuncSmallCastKey();

    static Size castToSize(const Key& key);

    virtual Size operator()(const Key& key) const override final;

    protected:
    static constexpr Size _small_key_mask{(Size(1) << (8 * sizeof(Key)))
                                          - Size(1)};
  };


  template < typename Key >
  class HashFuncMediumCastKey: public HashFuncBase< Key > {
    public:
    HashFuncMediumCastKey();

    static Size castToSize(const Key& key);

    virtual Size operator()(const Key& key) const override final;
  };


  template < typename Key >
  class HashFuncLargeCastKey: public HashFuncBase< Key > {
    public:
    HashFuncLargeCastKey();

    static Size castToSize(const Key& key);

    virtual Size operator()(const Key& key) const override final;
  };


  template < typename Key >
  struct HashFuncCastKey {
    using type = typename std::conditional<
       sizeof(Key) <= sizeof(Size) && std::is_integral< Key >::value,
       HashFuncSmallKey< Key >,
       typename std::conditional<
          sizeof(Key) < sizeof(Size),
          HashFuncSmallCastKey< Key >,
          typename std::conditional<
             sizeof(Key) == sizeof(Size),
             HashFuncMediumCastKey< Key >,
             typename std::conditional< sizeof(Key) == 2 * sizeof(Size),
                                        HashFuncLargeCastKey< Key >,
                                        void >::type >::type >::type >::type;
  };


  // ===========================================================================
  // ===   CLASSES FOR NOT DEFINING SEVERAL TIMES THE SAME HASH FUNCTIONS    ===
  // ===========================================================================

  // a dummy hash type
  template < typename Key >
  class dummyHash {};

  // the general type of the recursive type to select the appropriate hash function
  template < typename... >
  struct HashFuncConditionalType;

  // base of the recursive type to select the appropriate hash function
  template < typename Key >
  struct HashFuncConditionalType< Key > {
    using type = Key;
  };

  // base of the recursive type to select the appropriate hash function
  template < typename KEY_TYPE, typename TYPE >
  struct HashFuncConditionalType< KEY_TYPE, TYPE > {
    using type = typename std::conditional< std::is_same< KEY_TYPE, TYPE >::value,
                                            dummyHash< KEY_TYPE >,
                                            KEY_TYPE >::type;
  };

  template < typename KEY_TYPE, typename FIRST_TYPE, typename... OTHER_TYPES >
  struct HashFuncConditionalType< KEY_TYPE, FIRST_TYPE, OTHER_TYPES... > {
    using type = typename std::conditional<
       std::is_same< KEY_TYPE, FIRST_TYPE >::value,
       dummyHash< KEY_TYPE >,
       typename HashFuncConditionalType< KEY_TYPE, OTHER_TYPES... >::type >::type;
  };


  // ===========================================================================
  // ===                  HASH FUNCTIONS FOR PAIRS OF KEYS                   ===
  // ===========================================================================

  template < typename key >
  class HashFunc {};

  template < typename Key1, typename Key2 >
  class HashFunc< std::pair< Key1, Key2 > >:
      public HashFuncBase< std::pair< Key1, Key2 > > {
    public:
    static Size castToSize(const std::pair< Key1, Key2 >& key);

    virtual Size
       operator()(const std::pair< Key1, Key2 >& key) const override final;
  };


  // ===========================================================================
  // ===                      WIDELY USED HASH FUNCTIONS                     ===
  // ===========================================================================

  template <>
  class HashFunc< bool >: public HashFuncSmallKey< bool > {};

  template <>
  class HashFunc< int >: public HashFuncSmallKey< int > {};

  template <>
  class HashFunc< unsigned int >: public HashFuncSmallKey< unsigned int > {};

  template <>
  class HashFunc< long >: public HashFuncSmallKey< long > {};

  template <>
  class HashFunc< unsigned long >: public HashFuncSmallKey< unsigned long > {};

  template <>
  class HashFunc< typename HashFuncConditionalType< std::size_t,
                                                    unsigned long,
                                                    unsigned int,
                                                    long,
                                                    int >::type >:
      public HashFuncCastKey< std::size_t >::type {};

  template <>
  class HashFunc< float >: public HashFuncCastKey< float >::type {};

  template <>
  class HashFunc< double >: public HashFuncCastKey< double >::type {};

  template < typename Type >
  class HashFunc< Type* >: public HashFuncCastKey< Type* >::type {};

  template <>
  class HashFunc< std::string >: public HashFuncBase< std::string > {
    public:
    static Size castToSize(const std::string& key);

    virtual Size operator()(const std::string& key) const override final;
  };


  template <>
  class HashFunc< std::vector< Idx > >: public HashFuncBase< std::vector< Idx > > {
    public:
    static Size castToSize(const std::vector< Idx >& key);

    virtual Size operator()(const std::vector< Idx >& key) const override final;
  };


  template <>
  class HashFunc< Debug >: public HashFuncBase< Debug > {
    public:
    static Size castToSize(const Debug& key);

    virtual Size operator()(const Debug& key) const override final;

    template < typename OTHER_KEY >
    friend class HashFunc;
  };


  template < typename Type >
  class HashFunc< RefPtr< Type > >: public HashFuncBase< RefPtr< Type > > {
    public:
    static Size castToSize(const RefPtr< Type >& key);

    virtual Size operator()(const RefPtr< Type >& key) const override final;
  };

} /* namespace gum */


#ifndef GUM_NO_INLINE
#  include <agrum/tools/core/hashFunc_inl.h>
#endif /* GUM_NO_INLINE */

#include <agrum/tools/core/hashFunc_tpl.h>

#endif /* GUM_HASHFUNC_H */