Dogcows Code - chaz/yoink/blob - hash.tpp

   1 ////////////////////////////////////////////////////////////////////////////////
   2
   3 //   Author:    Andy Rushton
   4 //   Copyright: (c) Southampton University 1999-2004
   5 //              (c) Andy Rushton           2004-2009
   6 //   License:   BSD License, see ../docs/license.html
   7
   8 ////////////////////////////////////////////////////////////////////////////////
   9
  10 namespace stlplus
  11 {
  12
  13   ////////////////////////////////////////////////////////////////////////////////
  14   // the element stored in the hash
  15
  16   template<typename K, typename T, typename H, typename E>
  17   class hash_element
  18   {
  19   public:
  20     master_iterator<hash<K,T,H,E>, hash_element<K,T,H,E> > m_master;
  21     std::pair<const K, T> m_value;
  22     hash_element<K,T,H,E>* m_next;
  23     unsigned m_hash;
  24
  25     hash_element(const hash<K,T,H,E>* owner, const K& key, const T& data, unsigned hash) :
  26       m_master(owner,this), m_value(key,data), m_next(0), m_hash(hash)
  27       {
  28       }
  29
  30     hash_element(const hash<K,T,H,E>* owner, const std::pair<const K,T>& value, unsigned hash) :
  31       m_master(owner,this), m_value(value), m_next(0), m_hash(hash)
  32       {
  33       }
  34
  35     ~hash_element(void)
  36       {
  37         m_next = 0;
  38         m_hash = 0;
  39       }
  40
  41     const hash<K,T,H,E>* owner(void) const
  42       {
  43         return m_master.owner();
  44       }
  45
  46     // generate the bin number from the hash value and the owner's number of bins
  47     unsigned bin(void) const
  48       {
  49         return m_hash % (owner()->m_bins);
  50       }
  51   };
  52
  53   ////////////////////////////////////////////////////////////////////////////////
  54   // iterator
  55
  56   // null constructor
  57   template<typename K, typename T, class H, class E, typename V>
  58   hash_iterator<K,T,H,E,V>::hash_iterator(void)
  59   {
  60   }
  61
  62   // non-null constructor used from within the hash to construct a valid iterator
  63   template<typename K, typename T, class H, class E, typename V>
  64   hash_iterator<K,T,H,E,V>::hash_iterator(hash_element<K,T,H,E>* element) :
  65     safe_iterator<hash<K,T,H,E>,hash_element<K,T,H,E> >(element->m_master)
  66   {
  67   }
  68
  69   // constructor used to create an end iterator
  70   template<typename K, typename T, class H, class E, typename V>
  71   hash_iterator<K,T,H,E,V>::hash_iterator(const hash<K,T,H,E>* owner) :
  72     safe_iterator<hash<K,T,H,E>,hash_element<K,T,H,E> >(owner)
  73   {
  74   }
  75
  76   template<typename K, typename T, class H, class E, typename V>
  77   hash_iterator<K,T,H,E,V>::hash_iterator(const safe_iterator<hash<K,T,H,E>, hash_element<K,T,H,E> >& iterator) :
  78     safe_iterator<hash<K,T,H,E>,hash_element<K,T,H,E> >(iterator)
  79   {
  80   }
  81
  82   // destructor
  83
  84   template<typename K, typename T, class H, class E, typename V>
  85   hash_iterator<K,T,H,E,V>::~hash_iterator(void)
  86   {
  87   }
  88
  89   // mode conversions
  90
  91   template<typename K, typename T, class H, class E, typename V>
  92   TYPENAME hash_iterator<K,T,H,E,V>::const_iterator hash_iterator<K,T,H,E,V>::constify(void) const
  93   {
  94     return hash_iterator<K,T,H,E,const std::pair<const K,T> >(*this);
  95   }
  96
  97   template<typename K, typename T, class H, class E, typename V>
  98   TYPENAME hash_iterator<K,T,H,E,V>::iterator hash_iterator<K,T,H,E,V>::deconstify(void) const
  99   {
 100     return hash_iterator<K,T,H,E,std::pair<const K,T> >(*this);
 101   }
 102
 103   // increment operator looks for the next element in the table
 104   // if there isn't one, then this becomes an end() iterator with m_bin = m_bins
 105   template<typename K, typename T, class H, class E, typename V>
 106   TYPENAME hash_iterator<K,T,H,E,V>::this_iterator& hash_iterator<K,T,H,E,V>::operator ++ (void)
 107     throw(null_dereference,end_dereference)
 108   {
 109     this->assert_valid();
 110     if (this->node()->m_next)
 111       set(this->node()->m_next->m_master);
 112     else
 113     {
 114       // failing that, subsequent hash values are tried until either an element is found or there are no more bins
 115       // in which case it becomes an end() iterator
 116       hash_element<K,T,H,E>* element = 0;
 117       unsigned current_bin = this->node()->bin();
 118       for(current_bin++; !element && (current_bin < this->owner()->m_bins); current_bin++)
 119         element = this->owner()->m_values[current_bin];
 120       if (element)
 121         set(element->m_master);
 122       else
 123         this->set_end();
 124     }
 125     return *this;
 126   }
 127
 128   // post-increment is defined in terms of pre-increment
 129   template<typename K, typename T, class H, class E, typename V>
 130   TYPENAME hash_iterator<K,T,H,E,V>::this_iterator hash_iterator<K,T,H,E,V>::operator ++ (int)
 131     throw(null_dereference,end_dereference)
 132   {
 133     hash_iterator<K,T,H,E,V> old(*this);
 134     ++(*this);
 135     return old;
 136   }
 137
 138   // two iterators are equal if they point to the same element
 139   // both iterators must be non-null and belong to the same table
 140   template<typename K, typename T, class H, class E, typename V>
 141   bool hash_iterator<K,T,H,E,V>::operator == (const hash_iterator<K,T,H,E,V>& r) const
 142   {
 143     return equal(r);
 144   }
 145
 146   template<typename K, typename T, class H, class E, typename V>
 147   bool hash_iterator<K,T,H,E,V>::operator != (const hash_iterator<K,T,H,E,V>& r) const
 148   {
 149     return !operator==(r);
 150   }
 151
 152   template<typename K, typename T, class H, class E, typename V>
 153   bool hash_iterator<K,T,H,E,V>::operator < (const hash_iterator<K,T,H,E,V>& r) const
 154   {
 155     return compare(r) < 0;
 156   }
 157
 158   // iterator dereferencing is only legal on a non-null iterator
 159   template<typename K, typename T, class H, class E, typename V>
 160   V& hash_iterator<K,T,H,E,V>::operator*(void) const
 161     throw(null_dereference,end_dereference)
 162   {
 163     this->assert_valid();
 164     return this->node()->m_value;
 165   }
 166
 167   template<typename K, typename T, class H, class E, typename V>
 168   V* hash_iterator<K,T,H,E,V>::operator->(void) const
 169     throw(null_dereference,end_dereference)
 170   {
 171     return &(operator*());
 172   }
 173
 174   ////////////////////////////////////////////////////////////////////////////////
 175   // hash
 176
 177   // totally arbitrary initial size used for auto-rehashed tables
 178   static unsigned hash_default_bins = 127;
 179
 180   // constructor
 181   // tests whether the user wants auto-rehash
 182   // sets the rehash point to be a loading of 1.0 by setting it to the number of bins
 183   // uses the user's size unless this is zero, in which case implement the default
 184
 185   template<typename K, typename T, class H, class E>
 186   hash<K,T,H,E>::hash(unsigned bins) :
 187     m_rehash(bins), m_bins(bins > 0 ? bins : hash_default_bins), m_size(0), m_values(0)
 188   {
 189     m_values = new hash_element<K,T,H,E>*[m_bins];
 190     for (unsigned i = 0; i < m_bins; i++)
 191       m_values[i] = 0;
 192   }
 193
 194   template<typename K, typename T, class H, class E>
 195   hash<K,T,H,E>::~hash(void)
 196   {
 197     // delete all the elements
 198     clear();
 199     // and delete the data structure
 200     delete[] m_values;
 201     m_values = 0;
 202   }
 203
 204   // as usual, implement the copy constructor i.t.o. the assignment operator
 205
 206   template<typename K, typename T, class H, class E>
 207   hash<K,T,H,E>::hash(const hash<K,T,H,E>& right) :
 208     m_rehash(right.m_rehash), m_bins(right.m_bins), m_size(0), m_values(0)
 209   {
 210     m_values = new hash_element<K,T,H,E>*[right.m_bins];
 211     // copy the rehash behaviour as well as the size
 212     for (unsigned i = 0; i < m_bins; i++)
 213       m_values[i] = 0;
 214     *this = right;
 215   }
 216
 217   // assignment operator
 218   // this is done by copying the elements
 219   // the source and target hashes can be different sizes
 220   // the hash is self-copy safe, i.e. it is legal to say x = x;
 221
 222   template<typename K, typename T, class H, class E>
 223   hash<K,T,H,E>& hash<K,T,H,E>::operator = (const hash<K,T,H,E>& r)
 224   {
 225     // make self-copy safe
 226     if (&r == this) return *this;
 227     // remove all the existing elements
 228     clear();
 229     // copy the elements across - remember that this is rehashing because the two
 230     // tables can be different sizes so there is no quick way of doing this by
 231     // copying the lists
 232     for (hash_iterator<K,T,H,E,const std::pair<const K,T> > i = r.begin(); i != r.end(); ++i)
 233       insert(i->first, i->second);
 234     return *this;
 235   }
 236
 237   // number of values in the hash
 238   template<typename K, typename T, class H, class E>
 239   bool hash<K,T,H,E>::empty(void) const
 240   {
 241     return m_size == 0;
 242   }
 243
 244   template<typename K, typename T, class H, class E>
 245   unsigned hash<K,T,H,E>::size(void) const
 246   {
 247     return m_size;
 248   }
 249
 250   // equality
 251   template<typename K, typename T, class H, class E>
 252   bool hash<K,T,H,E>::operator == (const hash<K,T,H,E>& right) const
 253   {
 254     // this table is the same as the right table if they are the same table!
 255     if (&right == this) return true;
 256     // they must be the same size to be equal
 257     if (m_size != right.m_size) return false;
 258     // now every key in this must be in right and have the same data
 259     for (hash_iterator<K,T,H,E,const std::pair<const K,T> > i = begin(); i != end(); i++)
 260     {
 261       hash_iterator<K,T,H,E,const std::pair<const K,T> > found = right.find(i->first);
 262       if (found == right.end()) return false;
 263       if (!(i->second == found->second)) return false;
 264     }
 265     return true;
 266   }
 267
 268   // set up the hash to auto-rehash at a specific size
 269   // setting the rehash size to 0 forces manual rehashing
 270   template<typename K, typename T, class H, class E>
 271   void hash<K,T,H,E>::auto_rehash(void)
 272   {
 273     m_rehash = m_bins;
 274   }
 275
 276   template<typename K, typename T, class H, class E>
 277   void hash<K,T,H,E>::manual_rehash(void)
 278   {
 279     m_rehash = 0;
 280   }
 281
 282   // the rehash function
 283   // builds a new hash table and moves the elements (without copying) from the old to the new
 284   // I store the un-modulused hash value in the element for more efficient rehashing
 285   // passing 0 to the bins parameter does auto-rehashing
 286   // passing any other value forces the number of bins
 287
 288   template<typename K, typename T, class H, class E>
 289   void hash<K,T,H,E>::rehash(unsigned bins)
 290   {
 291     // user specified size: just take the user's value
 292     // auto calculate: if the load is high, increase the size; else do nothing
 293     unsigned new_bins = bins ? bins : m_bins;
 294     if (bins == 0 && m_size > 0)
 295     {
 296       // these numbers are pretty arbitrary
 297       // TODO - make them user-customisable?
 298       float load = loading();
 299       if (load > 2.0)
 300         new_bins = (unsigned)(m_bins * load);
 301       else if (load > 1.0)
 302         new_bins = m_bins * 2;
 303     }
 304     if (new_bins == m_bins) return;
 305     // set the new rehashing point if auto-rehashing is on
 306     if (m_rehash) m_rehash = new_bins;
 307     // move aside the old structure
 308     hash_element<K,T,H,E>** old_values = m_values;
 309     unsigned old_bins = m_bins;
 310     // create a replacement structure
 311     m_values = new hash_element<K,T,H,E>*[new_bins];
 312     for (unsigned i = 0; i < new_bins; i++)
 313       m_values[i] = 0;
 314     m_bins = new_bins;
 315     // move all the old elements across, rehashing each one
 316     for (unsigned j = 0; j < old_bins; j++)
 317     {
 318       while(old_values[j])
 319       {
 320         // unhook from the old structure
 321         hash_element<K,T,H,E>* current = old_values[j];
 322         old_values[j] = current->m_next;
 323         // rehash using the stored hash value
 324         unsigned bin = current->bin();
 325         // hook it into the new structure
 326         current->m_next = m_values[bin];
 327         m_values[bin] = current;
 328       }
 329     }
 330     // now delete the old structure
 331     delete[] old_values;
 332   }
 333
 334   // the loading is the average number of elements per bin
 335   // this simplifies to the total elements divided by the number of bins
 336
 337   template<typename K, typename T, class H, class E>
 338   float hash<K,T,H,E>::loading(void) const
 339   {
 340     return (float)m_size / (float)m_bins;
 341   }
 342
 343   // remove all elements from the table
 344
 345   template<typename K, typename T, class H, class E>
 346   void hash<K,T,H,E>::erase(void)
 347   {
 348     // unhook the list elements and destroy them
 349     for (unsigned i = 0; i < m_bins; i++)
 350     {
 351       hash_element<K,T,H,E>* current = m_values[i];
 352       while(current)
 353       {
 354         hash_element<K,T,H,E>* next = current->m_next;
 355         delete current;
 356         current = next;
 357       }
 358       m_values[i] = 0;
 359     }
 360     m_size = 0;
 361   }
 362
 363   // test for whether a key is present in the table
 364
 365   template<typename K, typename T, class H, class E>
 366   bool hash<K,T,H,E>::present(const K& key) const
 367   {
 368     return find(key) != end();
 369   }
 370
 371   template<typename K, typename T, class H, class E>
 372   TYPENAME hash<K,T,H,E>::size_type hash<K,T,H,E>::count(const K& key) const
 373   {
 374     return present() ? 1 : 0;
 375   }
 376
 377   // add a key and data element to the table - defined in terms of the general-purpose pair insert function
 378
 379   template<typename K, typename T, class H, class E>
 380   TYPENAME hash<K,T,H,E>::iterator hash<K,T,H,E>::insert(const K& key, const T& data)
 381   {
 382     return insert(std::pair<const K,T>(key,data)).first;
 383   }
 384
 385   // insert a key/data pair into the table
 386   // this removes any old value with the same key since there is no multihash functionality
 387
 388   template<typename K, typename T, class H, class E>
 389   std::pair<TYPENAME hash<K,T,H,E>::iterator, bool> hash<K,T,H,E>::insert(const std::pair<const K,T>& value)
 390   {
 391     // if auto-rehash is enabled, implement the auto-rehash before inserting the new value
 392     // the table is rehashed if this insertion makes the loading exceed 1.0
 393     if (m_rehash && (m_size >= m_rehash)) rehash();
 394     // calculate the new hash value
 395     unsigned hash_value_full = H()(value.first);
 396     unsigned bin = hash_value_full % m_bins;
 397     bool inserted = true;
 398     // unhook any previous value with this key
 399     // this has been inlined from erase(key) so that the hash value is not calculated twice
 400     hash_element<K,T,H,E>* previous = 0;
 401     for (hash_element<K,T,H,E>* current = m_values[bin]; current; previous = current, current = current->m_next)
 402     {
 403       // first check the full stored hash value
 404       if (current->m_hash != hash_value_full) continue;
 405
 406       // next try the equality operator
 407       if (!E()(current->m_value.first, value.first)) continue;
 408
 409       // unhook this value and destroy it
 410       if (previous)
 411         previous->m_next = current->m_next;
 412       else
 413         m_values[bin] = current->m_next;
 414       delete current;
 415       m_size--;
 416
 417       // we've overwritten a previous value
 418       inserted = false;
 419
 420       // assume there can only be one match so we can give up now
 421       break;
 422     }
 423     // now hook in a new list element at the start of the list for this hash value
 424     hash_element<K,T,H,E>* new_item = new hash_element<K,T,H,E>(this, value, hash_value_full);
 425     new_item->m_next = m_values[bin];
 426     m_values[bin] = new_item;
 427     // increment the size count
 428     m_size++;
 429     // construct an iterator from the list node, and return whether inserted
 430     return std::make_pair(hash_iterator<K,T,H,E,std::pair<const K,T> >(new_item), inserted);
 431   }
 432
 433   // insert a key with an empty data field ready to be filled in later
 434
 435   template<typename K, typename T, class H, class E>
 436   TYPENAME hash<K,T,H,E>::iterator hash<K,T,H,E>::insert(const K& key)
 437   {
 438     return insert(key,T());
 439   }
 440
 441   // remove a key from the table - return true if the key was found and removed, false if it wasn't present
 442
 443   template<typename K, typename T, class H, class E>
 444   bool hash<K,T,H,E>::erase(const K& key)
 445   {
 446     unsigned hash_value_full = H()(key);
 447     unsigned bin = hash_value_full % m_bins;
 448     // scan the list for an element with this key
 449     // need to keep a previous pointer because the lists are single-linked
 450     hash_element<K,T,H,E>* previous = 0;
 451     for (hash_element<K,T,H,E>* current = m_values[bin]; current; previous = current, current = current->m_next)
 452     {
 453       // first check the full stored hash value
 454       if (current->m_hash != hash_value_full) continue;
 455
 456       // next try the equality operator
 457       if (!E()(current->m_value.first, key)) continue;
 458
 459       // found this key, so unhook the element from the list
 460       if (previous)
 461         previous->m_next = current->m_next;
 462       else
 463         m_values[bin] = current->m_next;
 464       // destroy it
 465       delete current;
 466       // remember to maintain the size count
 467       m_size--;
 468       return true;
 469     }
 470     return false;
 471   }
 472
 473   template<typename K, typename T, class H, class E>
 474   void hash<K,T,H,E>::clear(void)
 475   {
 476     erase();
 477   }
 478
 479   // search for a key in the table and return an iterator to it
 480   // if the search fails, returns an end() iterator
 481
 482   template<typename K, typename T, class H, class E>
 483   TYPENAME hash<K,T,H,E>::const_iterator hash<K,T,H,E>::find(const K& key) const
 484   {
 485     // scan the list for this key's hash value for the element with a matching key
 486     unsigned hash_value_full = H()(key);
 487     unsigned bin = hash_value_full % m_bins;
 488     for (hash_element<K,T,H,E>* current = m_values[bin]; current; current = current->m_next)
 489     {
 490       if (current->m_hash == hash_value_full && E()(current->m_value.first, key))
 491         return hash_iterator<K,T,H,E,const std::pair<const K,T> >(current);
 492     }
 493     return end();
 494   }
 495
 496   template<typename K, typename T, class H, class E>
 497   TYPENAME hash<K,T,H,E>::iterator hash<K,T,H,E>::find(const K& key)
 498   {
 499     // scan the list for this key's hash value for the element with a matching key
 500     unsigned hash_value_full = H()(key);
 501     unsigned bin = hash_value_full % m_bins;
 502     for (hash_element<K,T,H,E>* current = m_values[bin]; current; current = current->m_next)
 503     {
 504       if (current->m_hash == hash_value_full && E()(current->m_value.first, key))
 505         return hash_iterator<K,T,H,E,std::pair<const K,T> >(current);
 506     }
 507     return end();
 508   }
 509
 510   // table lookup by key using the index operator[], returning a reference to the data field, not an iterator
 511   // this is rather like the std::map's [] operator
 512   // the difference is that I have a const and non-const version
 513   // the const version will not create the element if not present already, but the non-const version will
 514   // the non-const version is compatible with the behaviour of the map
 515
 516   template<typename K, typename T, class H, class E>
 517   const T& hash<K,T,H,E>::operator[] (const K& key) const throw(std::out_of_range)
 518   {
 519     // this const version cannot change the hash, so has to raise an exception if the key is missing
 520     hash_iterator<K,T,H,E,const std::pair<const K,T> > found = find(key);
 521     if (found == end())
 522       throw std::out_of_range("key not found in stlplus::hash::operator[]");
 523     return found->second;
 524   }
 525
 526   template<typename K, typename T, class H, class E>
 527   T& hash<K,T,H,E>::operator[] (const K& key)
 528   {
 529     // this non-const version can change the hash, so creates a new element if the key is missing
 530     hash_iterator<K,T,H,E,std::pair<const K,T> > found = find(key);
 531     if (found == end())
 532       found = insert(key);
 533     return found->second;
 534   }
 535
 536   // iterators
 537
 538   template<typename K, typename T, class H, class E>
 539   TYPENAME hash<K,T,H,E>::const_iterator hash<K,T,H,E>::begin(void) const
 540   {
 541     // find the first element
 542     for (unsigned bin = 0; bin < m_bins; bin++)
 543       if (m_values[bin])
 544         return hash_iterator<K,T,H,E,const std::pair<const K,T> >(m_values[bin]);
 545     // if the hash is empty, return the end iterator
 546     return end();
 547   }
 548
 549   template<typename K, typename T, class H, class E>
 550   TYPENAME hash<K,T,H,E>::iterator hash<K,T,H,E>::begin(void)
 551   {
 552     // find the first element
 553     for (unsigned bin = 0; bin < m_bins; bin++)
 554       if (m_values[bin])
 555         return hash_iterator<K,T,H,E,std::pair<const K,T> >(m_values[bin]);
 556     // if the hash is empty, return the end iterator
 557     return end();
 558   }
 559
 560   template<typename K, typename T, class H, class E>
 561   TYPENAME hash<K,T,H,E>::const_iterator hash<K,T,H,E>::end(void) const
 562   {
 563     return hash_iterator<K,T,H,E,const std::pair<const K,T> >(this);
 564   }
 565
 566   template<typename K, typename T, class H, class E>
 567   TYPENAME hash<K,T,H,E>::iterator hash<K,T,H,E>::end(void)
 568   {
 569     return hash_iterator<K,T,H,E,std::pair<const K,T> >(this);
 570   }
 571
 572   ////////////////////////////////////////////////////////////////////////////////
 573
 574 } // end namespace stlplus
 575