hashFunc_tpl.h

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/****************************************************************************
 *   This file is part of the aGrUM/pyAgrum library.                        *
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 *   Copyright (c) 2005-2026 by                                             *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
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 *   SPDX-FileCopyrightText: Copyright 2005-2026                            *
 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
 *       - Christophe GONZALES(_at_AMU)                                     *
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#pragma once
 

 
// to help IDE parser
#include <cstring>
 
#include <agrum/base/core/hashFunc.h>
 
#ifndef DOXYGEN_SHOULD_SKIP_THIS
 
namespace gum {
 
  // Update the hash function to take into account a resize of the hash table
  template < typename Key >
  void HashFuncBase< Key >::resize(const Size new_size) {
    // things work properly only for hashtables with at least 2 elements
    if (new_size < 2) {
      GUM_ERROR(SizeError,
                "the size of the hashtable must be at least 2 but a size of "
                    << new_size << " was provided to the resize function.");
    }
 
    hash_log2_size_ = _hashTableLog2_(new_size);
    hash_size_      = Size(1) << hash_log2_size_;
    hash_mask_      = hash_size_ - 1;
    right_shift_    = HashFuncConst::offset - hash_log2_size_;
  }
 
  // Returns the hash table size as known by the hash function
  template < typename Key >
  Size HashFuncBase< Key >::size() const {
    return hash_size_;
  }
 
  // ===========================================================================
 
  // constructor
  template < typename Key >
  HashFuncSmallKey< Key >::HashFuncSmallKey() {
    static_assert(std::is_integral_v< Key > && sizeof(Key) <= sizeof(Size),
                  "Error: you used HashFuncSmallKey for a key which cannot be "
                  "converted (without narrowing) into a gum::Size");
  }
 
  // Returns the value of a key as a Size
  template < typename Key >
  Size HashFuncSmallKey< Key >::castToSize(const Key& key) {
    return Size(key);
  }
 
  // Returns the hashed value of a key.
  template < typename Key >
  Size HashFuncSmallKey< Key >::operator()(const Key& key) const {
    return (castToSize(key) * HashFuncConst::gold) >> this->right_shift_;
  }
 
  // ===========================================================================
 
  // constructor
  template < typename Key >
  HashFuncSmallCastKey< Key >::HashFuncSmallCastKey() {
    static_assert(sizeof(Key) < sizeof(Size),
                  "Error: you used HashFuncSmallCastKey for a key whose size "
                  "is longer than or equal to that of gum::Size");
  }
 
  // Returns the value of a key as a Size
  template < typename Key >
  Size HashFuncSmallCastKey< Key >::castToSize(const Key& key) {
    // the code for MVSC differs from the code of the other compilers for
    // speed-up reasons: according to godbolt.org, the first code
    // should be twice faster than the second one
#  ifdef _MSC_VER
    return *((Size*)(&key)) & HashFuncSmallCastKey< Key >::small_key_mask_;
#  else
    Size result = 0;
    memcpy(&result, &key, sizeof(Key));
    return result;
#  endif /* _MSC_VER */
  }
 
  // Returns the hashed value of a key.
  template < typename Key >
  Size HashFuncSmallCastKey< Key >::operator()(const Key& key) const {
    return (castToSize(key) * HashFuncConst::gold) >> this->right_shift_;
  }
 
  // ===========================================================================
 
  // constructor
  template < typename Key >
  HashFuncMediumCastKey< Key >::HashFuncMediumCastKey() {
    static_assert(sizeof(Key) == sizeof(Size),
                  "Error: using HashFuncMediumCastKey for a key whose size "
                  "is different from that of a gum::Size");
  }
 
  // Returns the value of a key as a Size
  template < typename Key >
  Size HashFuncMediumCastKey< Key >::castToSize(const Key& key) {
    return *((Size*)(&key));
  }
 
  // Returns the hashed value of a key.
  template < typename Key >
  Size HashFuncMediumCastKey< Key >::operator()(const Key& key) const {
    return (castToSize(key) * HashFuncConst::gold) >> this->right_shift_;
  }
 
  // ===========================================================================
 
  // constructor
  template < typename Key >
  HashFuncLargeCastKey< Key >::HashFuncLargeCastKey() {
    static_assert(sizeof(Key) == 2 * sizeof(Size),
                  "Error: you used HashFuncLargeCastKey for a key whose size "
                  "is different from twice that of a gum::Size");
  }
 
  // Returns the value of a key as a Size
  template < typename Key >
  Size HashFuncLargeCastKey< Key >::castToSize(const Key& key) {
    const Size* ptr = reinterpret_cast< const Size* >(&key);
    return ptr[0] ^ ptr[1];
  }
 
  // Returns the hashed value of a key.
  template < typename Key >
  Size HashFuncLargeCastKey< Key >::operator()(const Key& key) const {
    return (castToSize(key) * HashFuncConst::gold) >> this->right_shift_;
  }
 
  // ===========================================================================
 
  // Returns the value of a key as a Size
  template < typename Key1, typename Key2 >
  Size HashFunc< std::pair< Key1, Key2 > >::castToSize(const std::pair< Key1, Key2 >& key) {
    return HashFunc< Key1 >::castToSize(key.first) * HashFuncConst::pi
         + HashFunc< Key2 >::castToSize(key.second);
  }
 
  // Returns the hashed value of a key.
  template < typename Key1, typename Key2 >
  Size HashFunc< std::pair< Key1, Key2 > >::operator()(const std::pair< Key1, Key2 >& key) const {
    return (castToSize(key) * HashFuncConst::gold) >> this->right_shift_;
  }
 
  // ===========================================================================
 
  // Returns the hashed value of a key.
  template < typename Type >
  Size HashFunc< std::shared_ptr< Type > >::castToSize(const std::shared_ptr< Type >& key) {
    return HashFunc< Type* >::castToSize(key.get());
  }
 
  // Returns the hashed value of a key.
  template < typename Type >
  Size HashFunc< std::shared_ptr< Type > >::operator()(const std::shared_ptr< Type >& key) const {
    return (castToSize(key) * HashFuncConst::gold) & this->hash_mask_;
  }
 
} /* namespace gum */
 
#endif /* DOXYGEN_SHOULD_SKIP_THIS */