// 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 sparse hashtable is a particular implementation of // a hashtable: one that is meant to minimize memory use. // It does this by using a *sparse table* (cf sparsetable.h), // which uses between 1 and 2 bits to store empty buckets // (we may need another bit for hashtables that support deletion). // // When empty buckets are so cheap, an appealing hashtable // implementation is 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. // // Deleted buckets are a bit of a pain. We have to somehow mark // deleted buckets (the probing must distinguish them from empty // buckets). The most principled way is to have another bitmap, // but that's annoying and takes up space. Instead we let the // user specify an "impossible" key. We set deleted buckets // to have the impossible key. // // 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. // // You probably shouldn't use this code directly. Use // or instead. // // You can modify the following, below: // HT_OCCUPANCY_FLT -- how full before we double size // HT_EMPTY_FLT -- how empty before we halve size // HT_MIN_BUCKETS -- smallest bucket size // HT_DEFAULT_STARTING_BUCKETS -- default bucket size at construct-time // // 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 // // The value type is required to be copy constructible and default // constructible, but it need not be (and commonly isn't) assignable. #ifndef _SPARSEHASHTABLE_H_ #define _SPARSEHASHTABLE_H_ #ifndef SPARSEHASH_STAT_UPDATE #define SPARSEHASH_STAT_UPDATE(x) ((void) 0) #endif // The probing method // Linear probing // #define JUMP_(key, num_probes) ( 1 ) // Quadratic-ish probing #define JUMP_(key, num_probes) ( num_probes ) // Hashtable class, used to implement the hashed associative containers // hash_set and hash_map. #include #include #include // For swap(), eg #include // for facts about iterator tags #include // for pair<> #include // Since that's basically what we are _START_GOOGLE_NAMESPACE_ using STL_NAMESPACE::pair; // Alloc is completely ignored. It is present as a template parameter only // for the sake of being compatible with the old SGI hashtable interface. // TODO(csilvers): is that the right thing to do? template class sparse_hashtable; template struct sparse_hashtable_iterator; template struct sparse_hashtable_const_iterator; // As far as iterating, we're basically just a sparsetable // that skips over deleted elements. template struct sparse_hashtable_iterator { public: typedef sparse_hashtable_iterator iterator; typedef sparse_hashtable_const_iterator const_iterator; typedef typename sparsetable::nonempty_iterator st_iterator; typedef STL_NAMESPACE::forward_iterator_tag iterator_category; typedef V value_type; typedef ptrdiff_t difference_type; typedef size_t size_type; typedef V& reference; // Value typedef V* pointer; // "Real" constructor and default constructor sparse_hashtable_iterator(const sparse_hashtable *h, st_iterator it, st_iterator it_end) : ht(h), pos(it), end(it_end) { advance_past_deleted(); } sparse_hashtable_iterator() { } // not ever used internally // 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 a marked-deleted array element void advance_past_deleted() { while ( pos != end && ht->test_deleted(*this) ) ++pos; } iterator& operator++() { assert(pos != end); ++pos; advance_past_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 sparse_hashtable *ht; st_iterator pos, end; }; // Now do it all again, but with const-ness! template struct sparse_hashtable_const_iterator { public: typedef sparse_hashtable_iterator iterator; typedef sparse_hashtable_const_iterator const_iterator; typedef typename sparsetable::const_nonempty_iterator st_iterator; typedef STL_NAMESPACE::forward_iterator_tag iterator_category; typedef V value_type; typedef ptrdiff_t difference_type; typedef size_t size_type; typedef const V& reference; // Value typedef const V* pointer; // "Real" constructor and default constructor sparse_hashtable_const_iterator(const sparse_hashtable *h, st_iterator it, st_iterator it_end) : ht(h), pos(it), end(it_end) { advance_past_deleted(); } // This lets us convert regular iterators to const iterators sparse_hashtable_const_iterator() { } // never used internally sparse_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 a marked-deleted array element void advance_past_deleted() { while ( pos != end && ht->test_deleted(*this) ) ++pos; } const_iterator& operator++() { assert(pos != end); ++pos; advance_past_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 sparse_hashtable *ht; st_iterator pos, end; }; // And once again, but this time freeing up memory as we iterate template struct sparse_hashtable_destructive_iterator { public: typedef sparse_hashtable_destructive_iterator iterator; typedef typename sparsetable::destructive_iterator st_iterator; typedef STL_NAMESPACE::forward_iterator_tag iterator_category; typedef V value_type; typedef ptrdiff_t difference_type; typedef size_t size_type; typedef V& reference; // Value typedef V* pointer; // "Real" constructor and default constructor sparse_hashtable_destructive_iterator(const sparse_hashtable *h, st_iterator it, st_iterator it_end) : ht(h), pos(it), end(it_end) { advance_past_deleted(); } sparse_hashtable_destructive_iterator() { } // never used internally // 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 a marked-deleted array element void advance_past_deleted() { while ( pos != end && ht->test_deleted(*this) ) ++pos; } iterator& operator++() { assert(pos != end); ++pos; advance_past_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 sparse_hashtable *ht; st_iterator pos, end; }; template class sparse_hashtable { public: typedef Key key_type; typedef Value value_type; typedef HashFcn hasher; typedef EqualKey key_equal; typedef size_t size_type; typedef 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 sparse_hashtable_iterator iterator; typedef sparse_hashtable_const_iterator const_iterator; typedef sparse_hashtable_destructive_iterator destructive_iterator; // 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 static const float HT_OCCUPANCY_FLT; // = 0.8f; // How empty we let the table get before we 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 minimum size is // determined by 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.nonempty_begin(), table.nonempty_end()); } iterator end() { return iterator(this, table.nonempty_end(), table.nonempty_end()); } const_iterator begin() const { return const_iterator(this, table.nonempty_begin(), table.nonempty_end()); } const_iterator end() const { return const_iterator(this, table.nonempty_end(), table.nonempty_end()); } // This is used when resizing destructive_iterator destructive_begin() { return destructive_iterator(this, table.destructive_begin(), table.destructive_end()); } destructive_iterator destructive_end() { return destructive_iterator(this, table.destructive_end(), table.destructive_end()); } // ACCESSOR FUNCTIONS for the things we templatize on, basically hasher hash_funct() const { return hash; } key_equal key_eq() const { return equals; } // We need to copy values when we set the special marker for deleted // elements, but, annoyingly, we can't just use the copy assignment // operator because value_type might not be assignable (it's often // pair). We use explicit destructor invocation and // placement new to get around this. Arg. private: void set_value(value_type* dst, const value_type src) { dst->~value_type(); // delete the old value, if any new(dst) value_type(src); } // This is used as a tag for the copy constructor, saying to destroy its // arg We have two ways of destructively copying: with potentially growing // the hashtable as we copy, and without. To make sure the outside world // can't do a destructive copy, we make the typename private. enum MoveDontCopyT {MoveDontCopy, MoveDontGrow}; // 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 sparse_hashtable tmp(MoveDontGrow, *this); swap(tmp); // now we are tmp } assert(num_deleted == 0); } public: void set_deleted_key(const value_type &val) { // It's only safe to change what "deleted" means if we purge deleted guys squash_deleted(); use_deleted = true; set_value(&delval, val); // save the key (and rest of val too) } 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 && table.test(bucknum) && equals(get_key(delval), get_key(table.get(bucknum)))); } bool test_deleted(const iterator &it) const { return (use_deleted && num_deleted > 0 && equals(get_key(delval), get_key(*it))); } bool test_deleted(const const_iterator &it) const { return (use_deleted && num_deleted > 0 && equals(get_key(delval), get_key(*it))); } bool test_deleted(const destructive_iterator &it) const { return (use_deleted && num_deleted > 0 && equals(get_key(delval), 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_value(const_cast(&(*it)), delval); 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); } // FUNCTIONS CONCERNING SIZE size_type size() const { return table.num_nonempty() - 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 table.size(); } size_type max_bucket_count() const { return max_size(); } 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; 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(table.num_nonempty() >= 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 && (table.num_nonempty()-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 && (table.num_nonempty() - num_deleted) <= sz * shrink_resize_percent ) sz /= 2; // stay a power of 2 sparse_hashtable tmp(MoveDontCopy, *this, sz); 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 && (table.num_nonempty() + 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(table.num_nonempty() + delta, 0); if ( needed_size > bucket_count() ) { // we don't have enough buckets const size_type resize_to = min_size(table.num_nonempty() - num_deleted + delta, 0); sparse_hashtable tmp(MoveDontCopy, *this, resize_to); swap(tmp); // now we are tmp } } // Used to actually do the rehashing when we grow/shrink a hashtable void copy_from(const sparse_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 table.resize(resize_to); // sets the number of buckets 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; table.test(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 } table.set(bucknum, *it); // copies the value to here } } // Implementation is like copy_from, but it destroys the table of the // "from" guy by freeing sparsetable memory as we iterate. This is // useful in resizing, since we're throwing away the "from" guy anyway. void move_from(MoveDontCopyT mover, sparse_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 size_t resize_to; if ( mover == MoveDontGrow ) resize_to = ht.bucket_count(); // keep same size as old ht else // MoveDontCopy resize_to = min_size(ht.size(), min_buckets_wanted); if ( resize_to > bucket_count() ) { // we don't have enough buckets table.resize(resize_to); // sets the number of buckets 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 // THIS IS THE MAJOR LINE THAT DIFFERS FROM COPY_FROM(): for ( destructive_iterator it = ht.destructive_begin(); it != ht.destructive_end(); ++it ) { size_type num_probes = 0; // how many times we've probed size_type bucknum; for ( bucknum = hash(get_key(*it)) & (bucket_count()-1); // h % buck_cnt table.test(bucknum); // not empty bucknum = (bucknum + JUMP_(key, num_probes)) & (bucket_count()-1) ) { ++num_probes; assert(num_probes < bucket_count()); // or else the hashtable is full } table.set(bucknum, *it); // copies the value to here } } // 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 ( consider_shrink || req_elements == 0 ) maybe_shrink(); if ( req_elements > table.num_nonempty() ) // we only grow resize_delta(req_elements - table.num_nonempty()); } // 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 set_resizing_parameters(float shrink, float grow) { assert(shrink >= 0.0); assert(grow <= 1.0); assert(shrink <= grow/2.0); 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 -- the default is fine, surprisingly. explicit sparse_hashtable(size_type expected_max_items_in_table = 0, const HashFcn& hf = HashFcn(), const EqualKey& eql = EqualKey(), const ExtractKey& ext = ExtractKey()) : hash(hf), equals(eql), get_key(ext), num_deleted(0), use_deleted(false), delval(), enlarge_resize_percent(HT_OCCUPANCY_FLT), shrink_resize_percent(HT_EMPTY_FLT), table(expected_max_items_in_table == 0 ? HT_DEFAULT_STARTING_BUCKETS : min_size(expected_max_items_in_table, 0)) { 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. // We also provide a mechanism of saying you want to "move" the ht argument // into us instead of copying. sparse_hashtable(const sparse_hashtable& ht, size_type min_buckets_wanted = HT_DEFAULT_STARTING_BUCKETS) : hash(ht.hash), equals(ht.equals), get_key(ht.get_key), num_deleted(0), use_deleted(ht.use_deleted), delval(ht.delval), enlarge_resize_percent(ht.enlarge_resize_percent), shrink_resize_percent(ht.shrink_resize_percent), table() { reset_thresholds(); copy_from(ht, min_buckets_wanted); // copy_from() ignores deleted entries } sparse_hashtable(MoveDontCopyT mover, sparse_hashtable& ht, size_type min_buckets_wanted = HT_DEFAULT_STARTING_BUCKETS) : hash(ht.hash), equals(ht.equals), get_key(ht.get_key), num_deleted(0), use_deleted(ht.use_deleted), delval(ht.delval), enlarge_resize_percent(ht.enlarge_resize_percent), shrink_resize_percent(ht.shrink_resize_percent), table() { reset_thresholds(); move_from(mover, ht, min_buckets_wanted); // ignores deleted entries } sparse_hashtable& operator= (const sparse_hashtable& ht) { if (&ht == this) return *this; // don't copy onto ourselves clear(); hash = ht.hash; equals = ht.equals; get_key = ht.get_key; use_deleted = ht.use_deleted; set_value(&delval, ht.delval); copy_from(ht, HT_MIN_BUCKETS); // sets num_deleted to 0 too return *this; } // Many STL algorithms use swap instead of copy constructors void swap(sparse_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(num_deleted, ht.num_deleted); STL_NAMESPACE::swap(use_deleted, ht.use_deleted); STL_NAMESPACE::swap(enlarge_resize_percent, ht.enlarge_resize_percent); STL_NAMESPACE::swap(shrink_resize_percent, ht.shrink_resize_percent); { value_type tmp; // for annoying reasons, swap() doesn't work set_value(&tmp, delval); set_value(&delval, ht.delval); set_value(&ht.delval, tmp); } table.swap(ht.table); reset_thresholds(); ht.reset_thresholds(); } // It's always nice to be able to clear a table without deallocating it void clear() { table.clear(); reset_thresholds(); 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 SPARSEHASH_STAT_UPDATE(total_lookups += 1); while ( 1 ) { // probe until something happens if ( !table.test(bucknum) ) { // bucket is empty SPARSEHASH_STAT_UPDATE(total_probes += num_probes); 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.get(bucknum))) ) { SPARSEHASH_STAT_UPDATE(total_probes += num_probes); 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.get_iter(pos.first), table.nonempty_end()); } 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.get_iter(pos.first), table.nonempty_end()); } // 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) { const iterator pos = find(key); // either an iterator or end return pair(pos, pos); } pair equal_range(const key_type& key) const { const const_iterator pos = find(key); // either an iterator or end return pair(pos, 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 delval assert(!use_deleted || !equals(get_key(obj), get_key(delval))); const pair pos = find_position(get_key(obj)); if ( pos.first != ILLEGAL_BUCKET) { // object was already there return pair(iterator(this, table.get_iter(pos.first), table.nonempty_end()), 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. // The set() below will undelete this object. We just worry about stats assert(num_deleted > 0); --num_deleted; // used to be, now it isn't } table.set(pos.second, obj); return pair(iterator(this, table.get_iter(pos.second), table.nonempty_end()), 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 erasing delval assert(!use_deleted || !equals(key, get_key(delval))); 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 sparse_hashtable& ht) const { // We really want to check that the hash functions are the same // but alas there's no way to do this. We just hope. return ( num_deleted == ht.num_deleted && table == ht.table ); } bool operator!=(const sparse_hashtable& ht) const { return !(*this == ht); } // I/O // We support reading and writing hashtables to disk. NOTE that // this only stores the hashtable metadata, not the stuff you've // actually put in the hashtable! 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. bool write_metadata(FILE *fp) { squash_deleted(); // so we don't have to worry about delkey return table.write_metadata(fp); } bool read_metadata(FILE *fp) { num_deleted = 0; // since we got rid before writing bool result = table.read_metadata(fp); reset_thresholds(); return result; } // Only meaningful if value_type is a POD. bool write_nopointer_data(FILE *fp) { return table.write_nopointer_data(fp); } // Only meaningful if value_type is a POD. bool read_nopointer_data(FILE *fp) { return table.read_nopointer_data(fp); } private: // The actual data hasher hash; // required by hashed_associative_container key_equal equals; ExtractKey get_key; size_type num_deleted; // how many occupied buckets are marked deleted bool use_deleted; // false until delval has been set value_type delval; // which key marks deleted entries float enlarge_resize_percent; // how full before resize float shrink_resize_percent; // how empty before resize size_type shrink_threshold; // table.size() * shrink_resize_percent size_type enlarge_threshold; // table.size() * enlarge_resize_percent sparsetable table; // holds num_buckets and num_elements too bool consider_shrink; // true if we should try to shrink before next insert void reset_thresholds() { enlarge_threshold = static_cast(table.size() * enlarge_resize_percent); shrink_threshold = static_cast(table.size() * shrink_resize_percent); consider_shrink = false; // whatever caused us to reset already considered } }; // We need a global swap as well template inline void swap(sparse_hashtable &x, sparse_hashtable &y) { x.swap(y); } #undef JUMP_ template const typename sparse_hashtable::size_type sparse_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 template const float sparse_hashtable::HT_OCCUPANCY_FLT = 0.8f; // 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 sparse_hashtable::HT_EMPTY_FLT = 0.4f * sparse_hashtable::HT_OCCUPANCY_FLT; _END_GOOGLE_NAMESPACE_ #endif /* _SPARSEHASHTABLE_H_ */