// Copyright (c) 2005, Google Inc. // All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following disclaimer // in the documentation and/or other materials provided with the // distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. // --- // Author: Craig Silverstein // // A dense hashtable is a particular implementation of // a hashtable: one that is meant to minimize memory allocation. // It does this by using an array to store all the data. We // steal a value from the key space to indicate "empty" array // elements (ie indices where no item lives) and another to indicate // "deleted" elements. // // (Note it is possible to change the value of the delete key // on the fly; you can even remove it, though after that point // the hashtable is insert_only until you set it again. The empty // value however can't be changed.) // // To minimize allocation and pointer overhead, we use internal // probing, in which the hashtable is a single table, and collisions // are resolved by trying to insert again in another bucket. The // most cache-efficient internal probing schemes are linear probing // (which suffers, alas, from clumping) and quadratic probing, which // is what we implement by default. // // Type requirements: value_type is required to be Copy Constructible // and Default Constructible. It is not required to be (and commonly // isn't) Assignable. // // You probably shouldn't use this code directly. Use // or instead. // You can change the following below: // HT_OCCUPANCY_PCT -- how full before we double size // HT_EMPTY_PCT -- how empty before we halve size // HT_MIN_BUCKETS -- default smallest bucket size // // You can also change enlarge_factor (which defaults to // HT_OCCUPANCY_PCT), and shrink_factor (which defaults to // HT_EMPTY_PCT) with set_resizing_parameters(). // // How to decide what values to use? // shrink_factor's default of .4 * OCCUPANCY_PCT, is probably good. // HT_MIN_BUCKETS is probably unnecessary since you can specify // (indirectly) the starting number of buckets at construct-time. // For enlarge_factor, you can use this chart to try to trade-off // expected lookup time to the space taken up. By default, this // code uses quadratic probing, though you can change it to linear // via _JUMP below if you really want to. // // From http://www.augustana.ca/~mohrj/courses/1999.fall/csc210/lecture_notes/hashing.html // NUMBER OF PROBES / LOOKUP Successful Unsuccessful // Quadratic collision resolution 1 - ln(1-L) - L/2 1/(1-L) - L - ln(1-L) // Linear collision resolution [1+1/(1-L)]/2 [1+1/(1-L)2]/2 // // -- enlarge_factor -- 0.10 0.50 0.60 0.75 0.80 0.90 0.99 // QUADRATIC COLLISION RES. // probes/successful lookup 1.05 1.44 1.62 2.01 2.21 2.85 5.11 // probes/unsuccessful lookup 1.11 2.19 2.82 4.64 5.81 11.4 103.6 // LINEAR COLLISION RES. // probes/successful lookup 1.06 1.5 1.75 2.5 3.0 5.5 50.5 // probes/unsuccessful lookup 1.12 2.5 3.6 8.5 13.0 50.0 5000.0 #ifndef _DENSEHASHTABLE_H_ #define _DENSEHASHTABLE_H_ // The probing method // Linear probing // #define JUMP_(key, num_probes) ( 1 ) // Quadratic probing #define JUMP_(key, num_probes) ( num_probes ) #include #include #include #include // for abort() #include // For swap(), eg #include // For length_error #include // For cerr #include // For uninitialized_fill, uninitialized_copy #include // for pair<> #include // for facts about iterator tags #include // for numeric_limits<> #include #include #include // for true_type, integral_constant, etc. _START_GOOGLE_NAMESPACE_ using STL_NAMESPACE::pair; // Hashtable class, used to implement the hashed associative containers // hash_set and hash_map. // Value: what is stored in the table (each bucket is a Value). // Key: something in a 1-to-1 correspondence to a Value, that can be used // to search for a Value in the table (find() takes a Key). // HashFcn: Takes a Key and returns an integer, the more unique the better. // ExtractKey: given a Value, returns the unique Key associated with it. // Must inherit from unary_function, or at least have a // result_type enum indicating the return type of operator(). // SetKey: given a Value* and a Key, modifies the value such that // ExtractKey(value) == key. We guarantee this is only called // with key == deleted_key or key == empty_key. // EqualKey: Given two Keys, says whether they are the same (that is, // if they are both associated with the same Value). // Alloc: STL allocator to use to allocate memory. template class dense_hashtable; template struct dense_hashtable_iterator; template struct dense_hashtable_const_iterator; // We're just an array, but we need to skip over empty and deleted elements template struct dense_hashtable_iterator { private: typedef typename A::template rebind::other value_alloc_type; public: typedef dense_hashtable_iterator iterator; typedef dense_hashtable_const_iterator const_iterator; typedef STL_NAMESPACE::forward_iterator_tag iterator_category; typedef V value_type; typedef typename value_alloc_type::difference_type difference_type; typedef typename value_alloc_type::size_type size_type; typedef typename value_alloc_type::reference reference; typedef typename value_alloc_type::pointer pointer; // "Real" constructor and default constructor dense_hashtable_iterator(const dense_hashtable *h, pointer it, pointer it_end, bool advance) : ht(h), pos(it), end(it_end) { if (advance) advance_past_empty_and_deleted(); } dense_hashtable_iterator() { } // The default destructor is fine; we don't define one // The default operator= is fine; we don't define one // Happy dereferencer reference operator*() const { return *pos; } pointer operator->() const { return &(operator*()); } // Arithmetic. The only hard part is making sure that // we're not on an empty or marked-deleted array element void advance_past_empty_and_deleted() { while ( pos != end && (ht->test_empty(*this) || ht->test_deleted(*this)) ) ++pos; } iterator& operator++() { assert(pos != end); ++pos; advance_past_empty_and_deleted(); return *this; } iterator operator++(int) { iterator tmp(*this); ++*this; return tmp; } // Comparison. bool operator==(const iterator& it) const { return pos == it.pos; } bool operator!=(const iterator& it) const { return pos != it.pos; } // The actual data const dense_hashtable *ht; pointer pos, end; }; // Now do it all again, but with const-ness! template struct dense_hashtable_const_iterator { private: typedef typename A::template rebind::other value_alloc_type; public: typedef dense_hashtable_iterator iterator; typedef dense_hashtable_const_iterator const_iterator; typedef STL_NAMESPACE::forward_iterator_tag iterator_category; typedef V value_type; typedef typename value_alloc_type::difference_type difference_type; typedef typename value_alloc_type::size_type size_type; typedef typename value_alloc_type::const_reference reference; typedef typename value_alloc_type::const_pointer pointer; // "Real" constructor and default constructor dense_hashtable_const_iterator( const dense_hashtable *h, pointer it, pointer it_end, bool advance) : ht(h), pos(it), end(it_end) { if (advance) advance_past_empty_and_deleted(); } dense_hashtable_const_iterator() : ht(NULL), pos(pointer()), end(pointer()) { } // This lets us convert regular iterators to const iterators dense_hashtable_const_iterator(const iterator &it) : ht(it.ht), pos(it.pos), end(it.end) { } // The default destructor is fine; we don't define one // The default operator= is fine; we don't define one // Happy dereferencer reference operator*() const { return *pos; } pointer operator->() const { return &(operator*()); } // Arithmetic. The only hard part is making sure that // we're not on an empty or marked-deleted array element void advance_past_empty_and_deleted() { while ( pos != end && (ht->test_empty(*this) || ht->test_deleted(*this)) ) ++pos; } const_iterator& operator++() { assert(pos != end); ++pos; advance_past_empty_and_deleted(); return *this; } const_iterator operator++(int) { const_iterator tmp(*this); ++*this; return tmp; } // Comparison. bool operator==(const const_iterator& it) const { return pos == it.pos; } bool operator!=(const const_iterator& it) const { return pos != it.pos; } // The actual data const dense_hashtable *ht; pointer pos, end; }; template class dense_hashtable { private: typedef typename Alloc::template rebind::other value_alloc_type; public: typedef Key key_type; typedef Value value_type; typedef HashFcn hasher; typedef EqualKey key_equal; typedef Alloc allocator_type; typedef typename value_alloc_type::size_type size_type; typedef typename value_alloc_type::difference_type difference_type; typedef typename value_alloc_type::reference reference; typedef typename value_alloc_type::const_reference const_reference; typedef typename value_alloc_type::pointer pointer; typedef typename value_alloc_type::const_pointer const_pointer; typedef dense_hashtable_iterator iterator; typedef dense_hashtable_const_iterator const_iterator; // These come from tr1. For us they're the same as regular iterators. typedef iterator local_iterator; typedef const_iterator const_local_iterator; // How full we let the table get before we resize, by default. // Knuth says .8 is good -- higher causes us to probe too much, // though it saves memory. static const int HT_OCCUPANCY_PCT; // = 50 (out of 100) // How empty we let the table get before we resize lower, by default. // (0.0 means never resize lower.) // It should be less than OCCUPANCY_PCT / 2 or we thrash resizing static const int HT_EMPTY_PCT; // = 0.4 * HT_OCCUPANCY_PCT; // Minimum size we're willing to let hashtables be. // Must be a power of two, and at least 4. // Note, however, that for a given hashtable, the initial size is a // function of the first constructor arg, and may be >HT_MIN_BUCKETS. static const size_type HT_MIN_BUCKETS = 4; // By default, if you don't specify a hashtable size at // construction-time, we use this size. Must be a power of two, and // at least HT_MIN_BUCKETS. static const size_type HT_DEFAULT_STARTING_BUCKETS = 32; // ITERATOR FUNCTIONS iterator begin() { return iterator(this, table, table + num_buckets, true); } iterator end() { return iterator(this, table + num_buckets, table + num_buckets, true); } const_iterator begin() const { return const_iterator(this, table, table+num_buckets,true);} const_iterator end() const { return const_iterator(this, table + num_buckets, table+num_buckets,true);} // These come from tr1 unordered_map. They iterate over 'bucket' n. // We'll just consider bucket n to be the n-th element of the table. local_iterator begin(size_type i) { return local_iterator(this, table + i, table + i+1, false); } local_iterator end(size_type i) { local_iterator it = begin(i); if (!test_empty(i) && !test_deleted(i)) ++it; return it; } const_local_iterator begin(size_type i) const { return const_local_iterator(this, table + i, table + i+1, false); } const_local_iterator end(size_type i) const { const_local_iterator it = begin(i); if (!test_empty(i) && !test_deleted(i)) ++it; return it; } // ACCESSOR FUNCTIONS for the things we templatize on, basically hasher hash_funct() const { return settings; } key_equal key_eq() const { return key_info; } allocator_type get_allocator() const { return allocator_type(val_info); } // Accessor function for statistics gathering. int num_table_copies() const { return settings.num_ht_copies(); } private: // Annoyingly, we can't copy values around, because they might have // const components (they're probably pair). We use // explicit destructor invocation and placement new to get around // this. Arg. void set_value(pointer dst, const_reference src) { dst->~value_type(); // delete the old value, if any new(dst) value_type(src); } void destroy_buckets(size_type first, size_type last) { for ( ; first != last; ++first) table[first].~value_type(); } // DELETE HELPER FUNCTIONS // This lets the user describe a key that will indicate deleted // table entries. This key should be an "impossible" entry -- // if you try to insert it for real, you won't be able to retrieve it! // (NB: while you pass in an entire value, only the key part is looked // at. This is just because I don't know how to assign just a key.) private: void squash_deleted() { // gets rid of any deleted entries we have if ( num_deleted ) { // get rid of deleted before writing dense_hashtable tmp(*this); // copying will get rid of deleted swap(tmp); // now we are tmp } assert(num_deleted == 0); } bool test_deleted_key(const key_type& key) const { // The num_deleted test is crucial for read(): after read(), the ht values // are garbage, and we don't want to think some of them are deleted. // Invariant: !use_deleted implies num_deleted is 0. assert(settings.use_deleted() || num_deleted == 0); return num_deleted > 0 && equals(key_info.delkey, key); } public: void set_deleted_key(const key_type &key) { // the empty indicator (if specified) and the deleted indicator // must be different assert((!settings.use_empty() || !equals(key, get_key(val_info.emptyval))) && "Passed the empty-key to set_deleted_key"); // It's only safe to change what "deleted" means if we purge deleted guys squash_deleted(); settings.set_use_deleted(true); key_info.delkey = key; } void clear_deleted_key() { squash_deleted(); settings.set_use_deleted(false); } key_type deleted_key() const { assert(settings.use_deleted() && "Must set deleted key before calling deleted_key"); return key_info.delkey; } // These are public so the iterators can use them // True if the item at position bucknum is "deleted" marker bool test_deleted(size_type bucknum) const { return test_deleted_key(get_key(table[bucknum])); } bool test_deleted(const iterator &it) const { return test_deleted_key(get_key(*it)); } bool test_deleted(const const_iterator &it) const { return test_deleted_key(get_key(*it)); } private: // Set it so test_deleted is true. true if object didn't used to be deleted. bool set_deleted(iterator &it) { assert(settings.use_deleted()); bool retval = !test_deleted(it); // &* converts from iterator to value-type. set_key(&(*it), key_info.delkey); return retval; } // Set it so test_deleted is false. true if object used to be deleted. bool clear_deleted(iterator &it) { assert(settings.use_deleted()); // Happens automatically when we assign something else in its place. return test_deleted(it); } // We also allow to set/clear the deleted bit on a const iterator. // We allow a const_iterator for the same reason you can delete a // const pointer: it's convenient, and semantically you can't use // 'it' after it's been deleted anyway, so its const-ness doesn't // really matter. bool set_deleted(const_iterator &it) { assert(settings.use_deleted()); bool retval = !test_deleted(it); set_key(const_cast(&(*it)), key_info.delkey); return retval; } // Set it so test_deleted is false. true if object used to be deleted. bool clear_deleted(const_iterator &it) { assert(settings.use_deleted()); return test_deleted(it); } // EMPTY HELPER FUNCTIONS // This lets the user describe a key that will indicate empty (unused) // table entries. This key should be an "impossible" entry -- // if you try to insert it for real, you won't be able to retrieve it! // (NB: while you pass in an entire value, only the key part is looked // at. This is just because I don't know how to assign just a key.) public: // These are public so the iterators can use them // True if the item at position bucknum is "empty" marker bool test_empty(size_type bucknum) const { assert(settings.use_empty()); // we always need to know what's empty! return equals(get_key(val_info.emptyval), get_key(table[bucknum])); } bool test_empty(const iterator &it) const { assert(settings.use_empty()); // we always need to know what's empty! return equals(get_key(val_info.emptyval), get_key(*it)); } bool test_empty(const const_iterator &it) const { assert(settings.use_empty()); // we always need to know what's empty! return equals(get_key(val_info.emptyval), get_key(*it)); } private: void fill_range_with_empty(pointer table_start, pointer table_end) { STL_NAMESPACE::uninitialized_fill(table_start, table_end, val_info.emptyval); } public: // TODO(csilvers): change all callers of this to pass in a key instead, // and take a const key_type instead of const value_type. void set_empty_key(const_reference val) { // Once you set the empty key, you can't change it assert(!settings.use_empty() && "Calling set_empty_key multiple times"); // The deleted indicator (if specified) and the empty indicator // must be different. assert((!settings.use_deleted() || !equals(get_key(val), key_info.delkey)) && "Setting the empty key the same as the deleted key"); settings.set_use_empty(true); set_value(&val_info.emptyval, val); assert(!table); // must set before first use // num_buckets was set in constructor even though table was NULL table = val_info.allocate(num_buckets); assert(table); fill_range_with_empty(table, table + num_buckets); } // TODO(sjackman): return a key_type rather than a value_type value_type empty_key() const { assert(settings.use_empty()); return val_info.emptyval; } // FUNCTIONS CONCERNING SIZE public: size_type size() const { return num_elements - num_deleted; } size_type max_size() const { return val_info.max_size(); } bool empty() const { return size() == 0; } size_type bucket_count() const { return num_buckets; } size_type max_bucket_count() const { return max_size(); } size_type nonempty_bucket_count() const { return num_elements; } // These are tr1 methods. Their idea of 'bucket' doesn't map well to // what we do. We just say every bucket has 0 or 1 items in it. size_type bucket_size(size_type i) const { return begin(i) == end(i) ? 0 : 1; } private: // Because of the above, size_type(-1) is never legal; use it for errors static const size_type ILLEGAL_BUCKET = size_type(-1); // Used after a string of deletes. Returns true if we actually shrunk. // TODO(csilvers): take a delta so we can take into account inserts // done after shrinking. Maybe make part of the Settings class? bool maybe_shrink() { assert(num_elements >= num_deleted); assert((bucket_count() & (bucket_count()-1)) == 0); // is a power of two assert(bucket_count() >= HT_MIN_BUCKETS); bool retval = false; // If you construct a hashtable with < HT_DEFAULT_STARTING_BUCKETS, // we'll never shrink until you get relatively big, and we'll never // shrink below HT_DEFAULT_STARTING_BUCKETS. Otherwise, something // like "dense_hash_set x; x.insert(4); x.erase(4);" will // shrink us down to HT_MIN_BUCKETS buckets, which is too small. const size_type num_remain = num_elements - num_deleted; const size_type shrink_threshold = settings.shrink_threshold(); if (shrink_threshold > 0 && num_remain < shrink_threshold && bucket_count() > HT_DEFAULT_STARTING_BUCKETS) { const float shrink_factor = settings.shrink_factor(); size_type sz = bucket_count() / 2; // find how much we should shrink while (sz > HT_DEFAULT_STARTING_BUCKETS && num_remain < sz * shrink_factor) { sz /= 2; // stay a power of 2 } dense_hashtable tmp(*this, sz); // Do the actual resizing swap(tmp); // now we are tmp retval = true; } settings.set_consider_shrink(false); // because we just considered it return retval; } // We'll let you resize a hashtable -- though this makes us copy all! // When you resize, you say, "make it big enough for this many more elements" // Returns true if we actually resized, false if size was already ok. bool resize_delta(size_type delta) { bool did_resize = false; if ( settings.consider_shrink() ) { // see if lots of deletes happened if ( maybe_shrink() ) did_resize = true; } if (num_elements >= (STL_NAMESPACE::numeric_limits::max)() - delta) throw std::length_error("resize overflow"); if ( bucket_count() >= HT_MIN_BUCKETS && (num_elements + delta) <= settings.enlarge_threshold() ) return did_resize; // we're ok as we are // Sometimes, we need to resize just to get rid of all the // "deleted" buckets that are clogging up the hashtable. So when // deciding whether to resize, count the deleted buckets (which // are currently taking up room). But later, when we decide what // size to resize to, *don't* count deleted buckets, since they // get discarded during the resize. const size_type needed_size = settings.min_buckets(num_elements + delta, 0); if ( needed_size <= bucket_count() ) // we have enough buckets return did_resize; size_type resize_to = settings.min_buckets(num_elements - num_deleted + delta, bucket_count()); if (resize_to < needed_size && // may double resize_to resize_to < (STL_NAMESPACE::numeric_limits::max)() / 2) { // This situation means that we have enough deleted elements, // that once we purge them, we won't actually have needed to // grow. But we may want to grow anyway: if we just purge one // element, say, we'll have to grow anyway next time we // insert. Might as well grow now, since we're already going // through the trouble of copying (in order to purge the // deleted elements). const size_type target = static_cast(settings.shrink_size(resize_to*2)); if (num_elements - num_deleted + delta >= target) { // Good, we won't be below the shrink threshhold even if we double. resize_to *= 2; } } dense_hashtable tmp(*this, resize_to); swap(tmp); // now we are tmp return true; } // We require table be not-NULL and empty before calling this. void resize_table(size_type /*old_size*/, size_type new_size, true_type) { table = val_info.realloc_or_die(table, new_size); } void resize_table(size_type old_size, size_type new_size, false_type) { val_info.deallocate(table, old_size); table = val_info.allocate(new_size); } // Used to actually do the rehashing when we grow/shrink a hashtable void copy_from(const dense_hashtable &ht, size_type min_buckets_wanted) { clear_to_size(settings.min_buckets(ht.size(), min_buckets_wanted)); // We use a normal iterator to get non-deleted bcks from ht // We could use insert() here, but since we know there are // no duplicates and no deleted items, we can be more efficient assert((bucket_count() & (bucket_count()-1)) == 0); // a power of two for ( const_iterator it = ht.begin(); it != ht.end(); ++it ) { size_type num_probes = 0; // how many times we've probed size_type bucknum; const size_type bucket_count_minus_one = bucket_count() - 1; for (bucknum = hash(get_key(*it)) & bucket_count_minus_one; !test_empty(bucknum); // not empty bucknum = (bucknum + JUMP_(key, num_probes)) & bucket_count_minus_one) { ++num_probes; assert(num_probes < bucket_count() && "Hashtable is full: an error in key_equal<> or hash<>"); } set_value(&table[bucknum], *it); // copies the value to here num_elements++; } settings.inc_num_ht_copies(); } // Required by the spec for hashed associative container public: // Though the docs say this should be num_buckets, I think it's much // more useful as num_elements. As a special feature, calling with // req_elements==0 will cause us to shrink if we can, saving space. void resize(size_type req_elements) { // resize to this or larger if ( settings.consider_shrink() || req_elements == 0 ) maybe_shrink(); if ( req_elements > num_elements ) resize_delta(req_elements - num_elements); } // Get and change the value of shrink_factor and enlarge_factor. The // description at the beginning of this file explains how to choose // the values. Setting the shrink parameter to 0.0 ensures that the // table never shrinks. void get_resizing_parameters(float* shrink, float* grow) const { *shrink = settings.shrink_factor(); *grow = settings.enlarge_factor(); } void set_resizing_parameters(float shrink, float grow) { settings.set_resizing_parameters(shrink, grow); settings.reset_thresholds(bucket_count()); } // CONSTRUCTORS -- as required by the specs, we take a size, // but also let you specify a hashfunction, key comparator, // and key extractor. We also define a copy constructor and =. // DESTRUCTOR -- needs to free the table explicit dense_hashtable(size_type expected_max_items_in_table = 0, const HashFcn& hf = HashFcn(), const EqualKey& eql = EqualKey(), const ExtractKey& ext = ExtractKey(), const SetKey& set = SetKey(), const Alloc& alloc = Alloc()) : settings(hf), key_info(ext, set, eql), num_deleted(0), num_elements(0), num_buckets(expected_max_items_in_table == 0 ? HT_DEFAULT_STARTING_BUCKETS : settings.min_buckets(expected_max_items_in_table, 0)), val_info(alloc_impl(alloc)), table(NULL) { // table is NULL until emptyval is set. However, we set num_buckets // here so we know how much space to allocate once emptyval is set settings.reset_thresholds(bucket_count()); } // As a convenience for resize(), we allow an optional second argument // which lets you make this new hashtable a different size than ht dense_hashtable(const dense_hashtable& ht, size_type min_buckets_wanted = HT_DEFAULT_STARTING_BUCKETS) : settings(ht.settings), key_info(ht.key_info), num_deleted(0), num_elements(0), num_buckets(0), val_info(ht.val_info), table(NULL) { if (!ht.settings.use_empty()) { // If use_empty isn't set, copy_from will crash, so we do our own copying. assert(ht.empty()); num_buckets = settings.min_buckets(ht.size(), min_buckets_wanted); settings.reset_thresholds(bucket_count()); return; } settings.reset_thresholds(bucket_count()); copy_from(ht, min_buckets_wanted); // copy_from() ignores deleted entries } dense_hashtable& operator= (const dense_hashtable& ht) { if (&ht == this) return *this; // don't copy onto ourselves if (!ht.settings.use_empty()) { assert(ht.empty()); dense_hashtable empty_table(ht); // empty table with ht's thresholds this->swap(empty_table); return *this; } settings = ht.settings; key_info = ht.key_info; set_value(&val_info.emptyval, ht.val_info.emptyval); // copy_from() calls clear and sets num_deleted to 0 too copy_from(ht, HT_MIN_BUCKETS); // we purposefully don't copy the allocator, which may not be copyable return *this; } ~dense_hashtable() { if (table) { destroy_buckets(0, num_buckets); val_info.deallocate(table, num_buckets); } } // Many STL algorithms use swap instead of copy constructors void swap(dense_hashtable& ht) { STL_NAMESPACE::swap(settings, ht.settings); STL_NAMESPACE::swap(key_info, ht.key_info); STL_NAMESPACE::swap(num_deleted, ht.num_deleted); STL_NAMESPACE::swap(num_elements, ht.num_elements); STL_NAMESPACE::swap(num_buckets, ht.num_buckets); { value_type tmp; // for annoying reasons, swap() doesn't work set_value(&tmp, val_info.emptyval); set_value(&val_info.emptyval, ht.val_info.emptyval); set_value(&ht.val_info.emptyval, tmp); } STL_NAMESPACE::swap(table, ht.table); settings.reset_thresholds(bucket_count()); // this also resets consider_shrink ht.settings.reset_thresholds(bucket_count()); // we purposefully don't swap the allocator, which may not be swap-able } private: void clear_to_size(size_type new_num_buckets) { if (!table) { table = val_info.allocate(new_num_buckets); } else { destroy_buckets(0, num_buckets); if (new_num_buckets != num_buckets) { // resize, if necessary typedef integral_constant >::value> realloc_ok; resize_table(num_buckets, new_num_buckets, realloc_ok()); } } assert(table); fill_range_with_empty(table, table + new_num_buckets); num_elements = 0; num_deleted = 0; num_buckets = new_num_buckets; // our new size settings.reset_thresholds(bucket_count()); } public: // It's always nice to be able to clear a table without deallocating it void clear() { // If the table is already empty, and the number of buckets is // already as we desire, there's nothing to do. const size_type new_num_buckets = settings.min_buckets(0, 0); if (num_elements == 0 && new_num_buckets == num_buckets) { return; } clear_to_size(new_num_buckets); } // Clear the table without resizing it. // Mimicks the stl_hashtable's behaviour when clear()-ing in that it // does not modify the bucket count void clear_no_resize() { if (num_elements > 0) { assert(table); destroy_buckets(0, num_buckets); fill_range_with_empty(table, table + num_buckets); } // don't consider to shrink before another erase() settings.reset_thresholds(bucket_count()); num_elements = 0; num_deleted = 0; } // LOOKUP ROUTINES private: // Returns a pair of positions: 1st where the object is, 2nd where // it would go if you wanted to insert it. 1st is ILLEGAL_BUCKET // if object is not found; 2nd is ILLEGAL_BUCKET if it is. // Note: because of deletions where-to-insert is not trivial: it's the // first deleted bucket we see, as long as we don't find the key later pair find_position(const key_type &key) const { size_type num_probes = 0; // how many times we've probed const size_type bucket_count_minus_one = bucket_count() - 1; size_type bucknum = hash(key) & bucket_count_minus_one; size_type insert_pos = ILLEGAL_BUCKET; // where we would insert while ( 1 ) { // probe until something happens if ( test_empty(bucknum) ) { // bucket is empty if ( insert_pos == ILLEGAL_BUCKET ) // found no prior place to insert return pair(ILLEGAL_BUCKET, bucknum); else return pair(ILLEGAL_BUCKET, insert_pos); } else if ( test_deleted(bucknum) ) {// keep searching, but mark to insert if ( insert_pos == ILLEGAL_BUCKET ) insert_pos = bucknum; } else if ( equals(key, get_key(table[bucknum])) ) { return pair(bucknum, ILLEGAL_BUCKET); } ++num_probes; // we're doing another probe bucknum = (bucknum + JUMP_(key, num_probes)) & bucket_count_minus_one; assert(num_probes < bucket_count() && "Hashtable is full: an error in key_equal<> or hash<>"); } } public: iterator find(const key_type& key) { if ( size() == 0 ) return end(); pair pos = find_position(key); if ( pos.first == ILLEGAL_BUCKET ) // alas, not there return end(); else return iterator(this, table + pos.first, table + num_buckets, false); } const_iterator find(const key_type& key) const { if ( size() == 0 ) return end(); pair pos = find_position(key); if ( pos.first == ILLEGAL_BUCKET ) // alas, not there return end(); else return const_iterator(this, table + pos.first, table+num_buckets, false); } // This is a tr1 method: the bucket a given key is in, or what bucket // it would be put in, if it were to be inserted. Shrug. size_type bucket(const key_type& key) const { pair pos = find_position(key); return pos.first == ILLEGAL_BUCKET ? pos.second : pos.first; } // Counts how many elements have key key. For maps, it's either 0 or 1. size_type count(const key_type &key) const { pair pos = find_position(key); return pos.first == ILLEGAL_BUCKET ? 0 : 1; } // Likewise, equal_range doesn't really make sense for us. Oh well. pair equal_range(const key_type& key) { iterator pos = find(key); // either an iterator or end if (pos == end()) { return pair(pos, pos); } else { const iterator startpos = pos++; return pair(startpos, pos); } } pair equal_range(const key_type& key) const { const_iterator pos = find(key); // either an iterator or end if (pos == end()) { return pair(pos, pos); } else { const const_iterator startpos = pos++; return pair(startpos, pos); } } // INSERTION ROUTINES private: // Private method used by insert_noresize and find_or_insert. iterator insert_at(const_reference obj, size_type pos) { if (size() >= max_size()) throw std::length_error("insert overflow"); if ( test_deleted(pos) ) { // just replace if it's been del. // shrug: shouldn't need to be const. const_iterator delpos(this, table + pos, table + num_buckets, false); clear_deleted(delpos); assert( num_deleted > 0); --num_deleted; // used to be, now it isn't } else { ++num_elements; // replacing an empty bucket } set_value(&table[pos], obj); return iterator(this, table + pos, table + num_buckets, false); } // If you know *this is big enough to hold obj, use this routine pair insert_noresize(const_reference obj) { // First, double-check we're not inserting delkey or emptyval assert((!settings.use_empty() || !equals(get_key(obj), get_key(val_info.emptyval))) && "Inserting the empty key"); assert((!settings.use_deleted() || !equals(get_key(obj), key_info.delkey)) && "Inserting the deleted key"); const pair pos = find_position(get_key(obj)); if ( pos.first != ILLEGAL_BUCKET) { // object was already there return pair(iterator(this, table + pos.first, table + num_buckets, false), false); // false: we didn't insert } else { // pos.second says where to put it return pair(insert_at(obj, pos.second), true); } } // Specializations of insert(it, it) depending on the power of the iterator: // (1) Iterator supports operator-, resize before inserting template void insert(ForwardIterator f, ForwardIterator l, STL_NAMESPACE::forward_iterator_tag) { size_t dist = STL_NAMESPACE::distance(f, l); if (dist >= (std::numeric_limits::max)()) throw std::length_error("insert-range overflow"); resize_delta(static_cast(dist)); for ( ; dist > 0; --dist, ++f) { insert_noresize(*f); } } // (2) Arbitrary iterator, can't tell how much to resize template void insert(InputIterator f, InputIterator l, STL_NAMESPACE::input_iterator_tag) { for ( ; f != l; ++f) insert(*f); } public: // This is the normal insert routine, used by the outside world pair insert(const_reference obj) { resize_delta(1); // adding an object, grow if need be return insert_noresize(obj); } // When inserting a lot at a time, we specialize on the type of iterator template void insert(InputIterator f, InputIterator l) { // specializes on iterator type insert(f, l, typename STL_NAMESPACE::iterator_traits::iterator_category()); } // DefaultValue is a functor that takes a key and returns a value_type // representing the default value to be inserted if none is found. template value_type& find_or_insert(const key_type& key) { // First, double-check we're not inserting emptykey or delkey assert((!settings.use_empty() || !equals(key, get_key(val_info.emptyval))) && "Inserting the empty key"); assert((!settings.use_deleted() || !equals(key, key_info.delkey)) && "Inserting the deleted key"); const pair pos = find_position(key); DefaultValue default_value; if ( pos.first != ILLEGAL_BUCKET) { // object was already there return table[pos.first]; } else if (resize_delta(1)) { // needed to rehash to make room // Since we resized, we can't use pos, so recalculate where to insert. return *insert_noresize(default_value(key)).first; } else { // no need to rehash, insert right here return *insert_at(default_value(key), pos.second); } } // DELETION ROUTINES size_type erase(const key_type& key) { // First, double-check we're not trying to erase delkey or emptyval. assert((!settings.use_empty() || !equals(key, get_key(val_info.emptyval))) && "Erasing the empty key"); assert((!settings.use_deleted() || !equals(key, key_info.delkey)) && "Erasing the deleted key"); const_iterator pos = find(key); // shrug: shouldn't need to be const if ( pos != end() ) { assert(!test_deleted(pos)); // or find() shouldn't have returned it set_deleted(pos); ++num_deleted; settings.set_consider_shrink(true); // will think about shrink after next insert return 1; // because we deleted one thing } else { return 0; // because we deleted nothing } } // We return the iterator past the deleted item. void erase(iterator pos) { if ( pos == end() ) return; // sanity check if ( set_deleted(pos) ) { // true if object has been newly deleted ++num_deleted; settings.set_consider_shrink(true); // will think about shrink after next insert } } void erase(iterator f, iterator l) { for ( ; f != l; ++f) { if ( set_deleted(f) ) // should always be true ++num_deleted; } settings.set_consider_shrink(true); // will think about shrink after next insert } // We allow you to erase a const_iterator just like we allow you to // erase an iterator. This is in parallel to 'delete': you can delete // a const pointer just like a non-const pointer. The logic is that // you can't use the object after it's erased anyway, so it doesn't matter // if it's const or not. void erase(const_iterator pos) { if ( pos == end() ) return; // sanity check if ( set_deleted(pos) ) { // true if object has been newly deleted ++num_deleted; settings.set_consider_shrink(true); // will think about shrink after next insert } } void erase(const_iterator f, const_iterator l) { for ( ; f != l; ++f) { if ( set_deleted(f) ) // should always be true ++num_deleted; } settings.set_consider_shrink(true); // will think about shrink after next insert } // COMPARISON bool operator==(const dense_hashtable& ht) const { if (size() != ht.size()) { return false; } else if (this == &ht) { return true; } else { // Iterate through the elements in "this" and see if the // corresponding element is in ht for ( const_iterator it = begin(); it != end(); ++it ) { const_iterator it2 = ht.find(get_key(*it)); if ((it2 == ht.end()) || (*it != *it2)) { return false; } } return true; } } bool operator!=(const dense_hashtable& ht) const { return !(*this == ht); } // I/O // We support reading and writing hashtables to disk. Alas, since // I don't know how to write a hasher or key_equal, you have to make // sure everything but the table is the same. We compact before writing // // NOTE: These functions are currently TODO. They've not been implemented. bool write_metadata(FILE * /*fp*/) { squash_deleted(); // so we don't have to worry about delkey return false; // TODO } bool read_metadata(FILE* /*fp*/) { num_deleted = 0; // since we got rid before writing assert(settings.use_empty() && "empty_key not set for read_metadata"); if (table) val_info.deallocate(table, num_buckets); // we'll make our own // TODO: read magic number // TODO: read num_buckets settings.reset_thresholds(bucket_count()); table = val_info.allocate(num_buckets); assert(table); fill_range_with_empty(table, table + num_buckets); // TODO: read num_elements for ( size_type i = 0; i < num_elements; ++i ) { // TODO: read bucket_num // TODO: set with non-empty, non-deleted value } return false; // TODO } // If your keys and values are simple enough, we can write them to // disk for you. "simple enough" means value_type is a POD type // that contains no pointers. However, we don't try to normalize // endianness bool write_nopointer_data(FILE *fp) const { for ( const_iterator it = begin(); it != end(); ++it ) { // TODO: skip empty/deleted values if ( !fwrite(&*it, sizeof(*it), 1, fp) ) return false; } return false; } // When reading, we have to override the potential const-ness of *it bool read_nopointer_data(FILE *fp) { for ( iterator it = begin(); it != end(); ++it ) { // TODO: skip empty/deleted values if ( !fread(reinterpret_cast(&(*it)), sizeof(*it), 1, fp) ) return false; } return false; } private: template class alloc_impl : public A { public: typedef typename A::pointer pointer; typedef typename A::size_type size_type; // Convert a normal allocator to one that has realloc_or_die() alloc_impl(const A& a) : A(a) { } // realloc_or_die should only be used when using the default // allocator (libc_allocator_with_realloc). pointer realloc_or_die(pointer /*ptr*/, size_type /*n*/) { fprintf(stderr, "realloc_or_die is only supported for " "libc_allocator_with_realloc"); exit(1); return NULL; } }; // A template specialization of alloc_impl for // libc_allocator_with_realloc that can handle realloc_or_die. template class alloc_impl > : public libc_allocator_with_realloc { public: typedef typename libc_allocator_with_realloc::pointer pointer; typedef typename libc_allocator_with_realloc::size_type size_type; alloc_impl(const libc_allocator_with_realloc& a) : libc_allocator_with_realloc(a) { } pointer realloc_or_die(pointer ptr, size_type n) { pointer retval = this->reallocate(ptr, n); if (retval == NULL) { // We really should use PRIuS here, but I don't want to have to add // a whole new configure option, with concomitant macro namespace // pollution, just to print this (unlikely) error message. So I cast. fprintf(stderr, "sparsehash: FATAL ERROR: failed to reallocate " "%lu elements for ptr %p", static_cast(n), ptr); exit(1); } return retval; } }; // Package allocator with emptyval to eliminate memory needed for // the zero-size allocator. // If new fields are added to this class, we should add them to // operator= and swap. class ValInfo : public alloc_impl { public: typedef typename alloc_impl::value_type value_type; ValInfo(const alloc_impl& a) : alloc_impl(a), emptyval() { } ValInfo(const ValInfo& v) : alloc_impl(v), emptyval(v.emptyval) { } value_type emptyval; // which key marks unused entries }; // Package functors with another class to eliminate memory needed for // zero-size functors. Since ExtractKey and hasher's operator() might // have the same function signature, they must be packaged in // different classes. struct Settings : sh_hashtable_settings { explicit Settings(const hasher& hf) : sh_hashtable_settings( hf, HT_OCCUPANCY_PCT / 100.0f, HT_EMPTY_PCT / 100.0f) {} }; // Packages ExtractKey and SetKey functors. class KeyInfo : public ExtractKey, public SetKey, public key_equal { public: KeyInfo(const ExtractKey& ek, const SetKey& sk, const key_equal& eq) : ExtractKey(ek), SetKey(sk), key_equal(eq) { } // We want to return the exact same type as ExtractKey: Key or const Key& typename ExtractKey::result_type get_key(const_reference v) const { return ExtractKey::operator()(v); } void set_key(pointer v, const key_type& k) const { SetKey::operator()(v, k); } bool equals(const key_type& a, const key_type& b) const { return key_equal::operator()(a, b); } // Which key marks deleted entries. // TODO(csilvers): make a pointer, and get rid of use_deleted (benchmark!) typename remove_const::type delkey; }; // Utility functions to access the templated operators size_type hash(const key_type& v) const { return settings.hash(v); } bool equals(const key_type& a, const key_type& b) const { return key_info.equals(a, b); } typename ExtractKey::result_type get_key(const_reference v) const { return key_info.get_key(v); } void set_key(pointer v, const key_type& k) const { key_info.set_key(v, k); } private: // Actual data Settings settings; KeyInfo key_info; size_type num_deleted; // how many occupied buckets are marked deleted size_type num_elements; size_type num_buckets; ValInfo val_info; // holds emptyval, and also the allocator pointer table; }; // We need a global swap as well template inline void swap(dense_hashtable &x, dense_hashtable &y) { x.swap(y); } #undef JUMP_ template const typename dense_hashtable::size_type dense_hashtable::ILLEGAL_BUCKET; // How full we let the table get before we resize. Knuth says .8 is // good -- higher causes us to probe too much, though saves memory. // However, we go with .5, getting better performance at the cost of // more space (a trade-off densehashtable explicitly chooses to make). // Feel free to play around with different values, though. template const int dense_hashtable::HT_OCCUPANCY_PCT = 50; // How empty we let the table get before we resize lower. // It should be less than OCCUPANCY_PCT / 2 or we thrash resizing template const int dense_hashtable::HT_EMPTY_PCT = static_cast(0.4 * dense_hashtable::HT_OCCUPANCY_PCT); _END_GOOGLE_NAMESPACE_ #endif /* _DENSEHASHTABLE_H_ */