// 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_FLT -- how full before we double size // HT_EMPTY_FLT -- how empty before we halve size // HT_MIN_BUCKETS -- default smallest bucket size // // You can also change enlarge_resize_percent (which defaults to // HT_OCCUPANCY_FLT), and shrink_resize_percent (which defaults to // HT_EMPTY_FLT) with set_resizing_parameters(). // // How to decide what values to use? // shrink_resize_percent's default of .4 * OCCUPANCY_FLT, is probably good. // HT_MIN_BUCKETS is probably unnecessary since you can specify // (indirectly) the starting number of buckets at construct-time. // For enlarge_resize_percent, 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_resize_percent -- 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-ish probing #define JUMP_(key, num_probes) ( num_probes ) #include "google/sparsehash/sparseconfig.h" #include #include #include // for abort() #include // For swap(), eg #include // For cerr #include // For uninitialized_fill, uninitialized_copy #include // for pair<> #include // for facts about iterator tags #include "google/type_traits.h" // 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. // 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. Currently ignored. 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 { 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 STL_NAMESPACE::ptrdiff_t difference_type; typedef size_t size_type; typedef V& reference; // Value typedef V* 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 { 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 STL_NAMESPACE::ptrdiff_t difference_type; typedef size_t size_type; typedef const V& reference; // Value typedef const V* 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() { } // 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 { public: typedef Key key_type; typedef Value value_type; typedef HashFcn hasher; typedef EqualKey key_equal; typedef size_t size_type; typedef STL_NAMESPACE::ptrdiff_t difference_type; typedef value_type* pointer; typedef const value_type* const_pointer; typedef value_type& reference; typedef const value_type& const_reference; 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 float HT_OCCUPANCY_FLT; // = 0.5; // 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_FLT / 2 or we thrash resizing static const float HT_EMPTY_FLT; // = 0.4 * HT_OCCUPANCY_FLT // 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_t 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_t 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. // For sparsehashtable, we could consider each 'group' to be a bucket, // I guess, but I don't really see the point. We'll just consider // bucket n to be the n-th element of the sparsetable, if it's occupied, // or some empty element, otherwise. 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 hash; } key_equal key_eq() const { return equals; } 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(value_type* dst, const value_type& src) { dst->~value_type(); 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); } public: void set_deleted_key(const key_type &key) { // the empty indicator (if specified) and the deleted indicator // must be different assert(!use_empty || !equals(key, get_key(emptyval))); // It's only safe to change what "deleted" means if we purge deleted guys squash_deleted(); use_deleted = true; delkey = key; } void clear_deleted_key() { squash_deleted(); use_deleted = false; } // 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 { // 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. return (use_deleted && num_deleted > 0 && equals(delkey, get_key(table[bucknum]))); } bool test_deleted(const iterator &it) const { return (use_deleted && num_deleted > 0 && equals(delkey, get_key(*it))); } bool test_deleted(const const_iterator &it) const { return (use_deleted && num_deleted > 0 && equals(delkey, get_key(*it))); } // Set it so test_deleted is true. true if object didn't used to be deleted // See below (at erase()) to explain why we allow const_iterators bool set_deleted(const_iterator &it) { assert(use_deleted); // bad if set_deleted_key() wasn't called bool retval = !test_deleted(it); // &* converts from iterator to value-type set_key(const_cast(&(*it)), delkey); return retval; } // Set it so test_deleted is false. true if object used to be deleted bool clear_deleted(const_iterator &it) { assert(use_deleted); // bad if set_deleted_key() wasn't called // happens automatically when we assign something else in its place 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(use_empty); // we always need to know what's empty! return equals(get_key(emptyval), get_key(table[bucknum])); } bool test_empty(const iterator &it) const { assert(use_empty); // we always need to know what's empty! return equals(get_key(emptyval), get_key(*it)); } bool test_empty(const const_iterator &it) const { assert(use_empty); // we always need to know what's empty! return equals(get_key(emptyval), get_key(*it)); } private: // You can either set a range empty or an individual element void set_empty(size_type bucknum) { assert(use_empty); set_value(&table[bucknum], emptyval); } void fill_range_with_empty(value_type* table_start, value_type* table_end) { // Like set_empty(range), but doesn't destroy previous contents STL_NAMESPACE::uninitialized_fill(table_start, table_end, emptyval); } void set_empty(size_type buckstart, size_type buckend) { assert(use_empty); destroy_buckets(buckstart, buckend); fill_range_with_empty(table + buckstart, table + buckend); } 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 value_type &val) { // Once you set the empty key, you can't change it assert(!use_empty); // The deleted indicator (if specified) and the empty indicator // must be different. assert(!use_deleted || !equals(get_key(val), delkey)); use_empty = true; set_value(&emptyval, val); assert(!table); // must set before first use // num_buckets was set in constructor even though table was NULL table = (value_type *) malloc(num_buckets * sizeof(*table)); assert(table); fill_range_with_empty(table, table + num_buckets); } // FUNCTIONS CONCERNING SIZE public: size_type size() const { return num_elements - num_deleted; } // Buckets are always a power of 2 size_type max_size() const { return (size_type(-1) >> 1U) + 1; } 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); private: // This is the smallest size a hashtable can be without being too crowded // If you like, you can give a min #buckets as well as a min #elts size_type min_size(size_type num_elts, size_type min_buckets_wanted) { size_type sz = HT_MIN_BUCKETS; // min buckets allowed while ( sz < min_buckets_wanted || num_elts >= sz * enlarge_resize_percent ) sz *= 2; return sz; } // Used after a string of deletes void 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); // 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. if (shrink_threshold > 0 && (num_elements-num_deleted) < shrink_threshold && bucket_count() > HT_DEFAULT_STARTING_BUCKETS ) { size_type sz = bucket_count() / 2; // find how much we should shrink while ( sz > HT_DEFAULT_STARTING_BUCKETS && (num_elements - num_deleted) < sz * shrink_resize_percent ) sz /= 2; // stay a power of 2 dense_hashtable tmp(*this, sz); // Do the actual resizing swap(tmp); // now we are tmp } consider_shrink = false; // because we just considered it } // 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" void resize_delta(size_type delta) { if ( consider_shrink ) // see if lots of deletes happened maybe_shrink(); if ( bucket_count() > HT_MIN_BUCKETS && (num_elements + delta) <= enlarge_threshold ) return; // 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 = min_size(num_elements + delta, 0); if ( needed_size > bucket_count() ) { // we don't have enough buckets const size_type resize_to = min_size(num_elements - num_deleted + delta, 0); dense_hashtable tmp(*this, resize_to); swap(tmp); // now we are tmp } } // Increase number of buckets, assuming value_type has trivial copy // constructor and destructor. (Really, we want it to have "trivial // move", because that's what realloc does. But there's no way to // capture that using type_traits, so we pretend that move(x, y) is // equivalent to "x.~T(); new(x) T(y);" which is pretty much // correct, if a bit conservative.) void expand_array(size_t resize_to, true_type) { table = (value_type *) realloc(table, resize_to * sizeof(value_type)); assert(table); fill_range_with_empty(table + num_buckets, table + resize_to); } // Increase number of buckets, without special assumptions about value_type. // TODO(austern): make this exception safe. Handle exceptions from // value_type's copy constructor. void expand_array(size_t resize_to, false_type) { value_type* new_table = (value_type *) malloc(resize_to * sizeof(value_type)); assert(new_table); STL_NAMESPACE::uninitialized_copy(table, table + num_buckets, new_table); fill_range_with_empty(new_table + num_buckets, new_table + resize_to); destroy_buckets(0, num_buckets); free(table); table = new_table; } // 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(); // clear table, set num_deleted to 0 // If we need to change the size of our table, do it now const size_type resize_to = min_size(ht.size(), min_buckets_wanted); if ( resize_to > bucket_count() ) { // we don't have enough buckets typedef integral_constant::value && has_trivial_destructor::value)> realloc_ok; // we pretend mv(x,y) == "x.~T(); new(x) T(y)" expand_array(resize_to, realloc_ok()); num_buckets = resize_to; reset_thresholds(); } // 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()); // or else the hashtable is full } set_value(&table[bucknum], *it); // copies the value to here num_elements++; } } // 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 req_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 ( consider_shrink || req_elements == 0 ) maybe_shrink(); if ( req_elements > num_elements ) return resize_delta(req_elements - num_elements); } // Get and change the value of shrink_resize_percent and // enlarge_resize_percent. 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 = shrink_resize_percent; *grow = enlarge_resize_percent; } void set_resizing_parameters(float shrink, float grow) { assert(shrink >= 0.0); assert(grow <= 1.0); if (shrink > grow/2.0f) shrink = grow / 2.0f; // otherwise we thrash hashtable size shrink_resize_percent = shrink; enlarge_resize_percent = grow; reset_thresholds(); } // 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()) : hash(hf), equals(eql), get_key(ext), set_key(set), num_deleted(0), use_deleted(false), use_empty(false), delkey(), emptyval(), enlarge_resize_percent(HT_OCCUPANCY_FLT), shrink_resize_percent(HT_EMPTY_FLT), table(NULL), num_buckets(expected_max_items_in_table == 0 ? HT_DEFAULT_STARTING_BUCKETS : min_size(expected_max_items_in_table, 0)), num_elements(0) { // 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 reset_thresholds(); } // 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) : hash(ht.hash), equals(ht.equals), get_key(ht.get_key), set_key(ht.set_key), num_deleted(0), use_deleted(ht.use_deleted), use_empty(ht.use_empty), delkey(ht.delkey), emptyval(ht.emptyval), enlarge_resize_percent(ht.enlarge_resize_percent), shrink_resize_percent(ht.shrink_resize_percent), table(NULL), num_buckets(0), num_elements(0) { reset_thresholds(); 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 clear(); hash = ht.hash; equals = ht.equals; get_key = ht.get_key; set_key = ht.set_key; use_deleted = ht.use_deleted; use_empty = ht.use_empty; delkey = ht.delkey; set_value(&emptyval, ht.emptyval); enlarge_resize_percent = ht.enlarge_resize_percent; shrink_resize_percent = ht.shrink_resize_percent; copy_from(ht, HT_MIN_BUCKETS); // sets num_deleted to 0 too return *this; } ~dense_hashtable() { if (table) { destroy_buckets(0, num_buckets); free(table); } } // Many STL algorithms use swap instead of copy constructors void swap(dense_hashtable& ht) { STL_NAMESPACE::swap(hash, ht.hash); STL_NAMESPACE::swap(equals, ht.equals); STL_NAMESPACE::swap(get_key, ht.get_key); STL_NAMESPACE::swap(set_key, ht.set_key); STL_NAMESPACE::swap(num_deleted, ht.num_deleted); STL_NAMESPACE::swap(use_deleted, ht.use_deleted); STL_NAMESPACE::swap(use_empty, ht.use_empty); STL_NAMESPACE::swap(enlarge_resize_percent, ht.enlarge_resize_percent); STL_NAMESPACE::swap(shrink_resize_percent, ht.shrink_resize_percent); STL_NAMESPACE::swap(delkey, ht.delkey); { value_type tmp; // for annoying reasons, swap() doesn't work set_value(&tmp, emptyval); set_value(&emptyval, ht.emptyval); set_value(&ht.emptyval, tmp); } STL_NAMESPACE::swap(table, ht.table); STL_NAMESPACE::swap(num_buckets, ht.num_buckets); STL_NAMESPACE::swap(num_elements, ht.num_elements); reset_thresholds(); ht.reset_thresholds(); } // It's always nice to be able to clear a table without deallocating it void clear() { if (table) destroy_buckets(0, num_buckets); num_buckets = min_size(0,0); // our new size reset_thresholds(); table = (value_type *) realloc(table, num_buckets * sizeof(*table)); assert(table); fill_range_with_empty(table, table + num_buckets); num_elements = 0; num_deleted = 0; } // 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 (table) { set_empty(0, num_buckets); } // don't consider to shrink before another erase() reset_thresholds(); 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()); // don't probe too many times! } } 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: // If you know *this is big enough to hold obj, use this routine pair insert_noresize(const value_type& obj) { // First, double-check we're not inserting delkey or emptyval assert(!use_empty || !equals(get_key(obj), get_key(emptyval))); assert(!use_deleted || !equals(get_key(obj), delkey)); 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 if ( test_deleted(pos.second) ) { // just replace if it's been del. const_iterator delpos(this, table + pos.second, // shrug: table + num_buckets, false);// shouldn't need const 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.second], obj); return pair(iterator(this, table + pos.second, table + num_buckets, false), true); // true: we did insert } } public: // This is the normal insert routine, used by the outside world pair insert(const value_type& 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()); } // Iterator supports operator-, resize before inserting template void insert(ForwardIterator f, ForwardIterator l, STL_NAMESPACE::forward_iterator_tag) { size_type n = STL_NAMESPACE::distance(f, l); // TODO(csilvers): standard? resize_delta(n); for ( ; n > 0; --n, ++f) insert_noresize(*f); } // 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); } // DELETION ROUTINES size_type erase(const key_type& key) { // First, double-check we're not trying to erase delkey or emptyval assert(!use_empty || !equals(key, get_key(emptyval))); assert(!use_deleted || !equals(key, delkey)); 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; consider_shrink = true; // will think about shrink after next insert return 1; // because we deleted one thing } else { return 0; // because we deleted nothing } } // This is really evil: really it should be iterator, not const_iterator. // But...the only reason keys are const is to allow lookup. // Since that's a moot issue for deleted keys, we allow const_iterators void erase(const_iterator pos) { if ( pos == end() ) return; // sanity check if ( set_deleted(pos) ) { // true if object has been newly deleted ++num_deleted; 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; } 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(use_empty); // have to set this before calling us if (table) free(table); // we'll make our own // TODO: read magic number // TODO: read num_buckets reset_thresholds(); table = (value_type *) malloc(num_buckets * sizeof(*table)); 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: // The actual data hasher hash; // required by hashed_associative_container key_equal equals; ExtractKey get_key; SetKey set_key; size_type num_deleted; // how many occupied buckets are marked deleted bool use_deleted; // false until delkey has been set bool use_empty; // you must do this before you start // TODO(csilvers): make a pointer, and get rid of use_deleted (benchmark!) key_type delkey; // which key marks deleted entries value_type emptyval; // which key marks unused entries float enlarge_resize_percent; // how full before resize float shrink_resize_percent; // how empty before resize size_type shrink_threshold; // num_buckets * shrink_resize_percent size_type enlarge_threshold; // num_buckets * enlarge_resize_percent value_type *table; size_type num_buckets; size_type num_elements; bool consider_shrink; // true if we should try to shrink before next insert void reset_thresholds() { enlarge_threshold = static_cast(num_buckets * enlarge_resize_percent); shrink_threshold = static_cast(num_buckets * shrink_resize_percent); consider_shrink = false; // whatever caused us to reset already considered } }; // 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 float dense_hashtable::HT_OCCUPANCY_FLT = 0.5f; // How empty we let the table get before we resize lower. // It should be less than OCCUPANCY_FLT / 2 or we thrash resizing template const float dense_hashtable::HT_EMPTY_FLT = 0.4f * dense_hashtable::HT_OCCUPANCY_FLT; _END_GOOGLE_NAMESPACE_ #endif /* _DENSEHASHTABLE_H_ */