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add sparsehash/densehashmap headers - a faster hashmap impl for our p…
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…urposes - refs #1629
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Dane Springmeyer committed Dec 7, 2012
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// 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.

// ----
//
// This is just a very thin wrapper over densehashtable.h, just
// like sgi stl's stl_hash_map is a very thin wrapper over
// stl_hashtable. The major thing we define is operator[], because
// we have a concept of a data_type which stl_hashtable doesn't
// (it only has a key and a value).
//
// NOTE: this is exactly like sparse_hash_map.h, with the word
// "sparse" replaced by "dense", except for the addition of
// set_empty_key().
//
// YOU MUST CALL SET_EMPTY_KEY() IMMEDIATELY AFTER CONSTRUCTION.
//
// Otherwise your program will die in mysterious ways. (Note if you
// use the constructor that takes an InputIterator range, you pass in
// the empty key in the constructor, rather than after. As a result,
// this constructor differs from the standard STL version.)
//
// In other respects, we adhere mostly to the STL semantics for
// hash-map. One important exception is that insert() may invalidate
// iterators entirely -- STL semantics are that insert() may reorder
// iterators, but they all still refer to something valid in the
// hashtable. Not so for us. Likewise, insert() may invalidate
// pointers into the hashtable. (Whether insert invalidates iterators
// and pointers depends on whether it results in a hashtable resize).
// On the plus side, delete() doesn't invalidate iterators or pointers
// at all, or even change the ordering of elements.
//
// Here are a few "power user" tips:
//
// 1) set_deleted_key():
// If you want to use erase() you *must* call set_deleted_key(),
// in addition to set_empty_key(), after construction.
// The deleted and empty keys must differ.
//
// 2) resize(0):
// When an item is deleted, its memory isn't freed right
// away. This allows you to iterate over a hashtable,
// and call erase(), without invalidating the iterator.
// To force the memory to be freed, call resize(0).
// For tr1 compatibility, this can also be called as rehash(0).
//
// 3) min_load_factor(0.0)
// Setting the minimum load factor to 0.0 guarantees that
// the hash table will never shrink.
//
// Roughly speaking:
// (1) dense_hash_map: fastest, uses the most memory unless entries are small
// (2) sparse_hash_map: slowest, uses the least memory
// (3) hash_map / unordered_map (STL): in the middle
//
// Typically I use sparse_hash_map when I care about space and/or when
// I need to save the hashtable on disk. I use hash_map otherwise. I
// don't personally use dense_hash_set ever; some people use it for
// small sets with lots of lookups.
//
// - dense_hash_map has, typically, about 78% memory overhead (if your
// data takes up X bytes, the hash_map uses .78X more bytes in overhead).
// - sparse_hash_map has about 4 bits overhead per entry.
// - sparse_hash_map can be 3-7 times slower than the others for lookup and,
// especially, inserts. See time_hash_map.cc for details.
//
// See /usr/(local/)?doc/sparsehash-*/dense_hash_map.html
// for information about how to use this class.

#ifndef _DENSE_HASH_MAP_H_
#define _DENSE_HASH_MAP_H_

#include <sparsehash/internal/sparseconfig.h>
#include <algorithm> // needed by stl_alloc
#include <functional> // for equal_to<>, select1st<>, etc
#include <memory> // for alloc
#include <utility> // for pair<>
#include <sparsehash/internal/densehashtable.h> // IWYU pragma: export
#include <sparsehash/internal/libc_allocator_with_realloc.h>
#include HASH_FUN_H // for hash<>
_START_GOOGLE_NAMESPACE_

template <class Key, class T,
class HashFcn = SPARSEHASH_HASH<Key>, // defined in sparseconfig.h
class EqualKey = std::equal_to<Key>,
class Alloc = libc_allocator_with_realloc<std::pair<const Key, T> > >
class dense_hash_map {
private:
// Apparently select1st is not stl-standard, so we define our own
struct SelectKey {
typedef const Key& result_type;
const Key& operator()(const std::pair<const Key, T>& p) const {
return p.first;
}
};
struct SetKey {
void operator()(std::pair<const Key, T>* value, const Key& new_key) const {
*const_cast<Key*>(&value->first) = new_key;
// It would be nice to clear the rest of value here as well, in
// case it's taking up a lot of memory. We do this by clearing
// the value. This assumes T has a zero-arg constructor!
value->second = T();
}
};
// For operator[].
struct DefaultValue {
std::pair<const Key, T> operator()(const Key& key) {
return std::make_pair(key, T());
}
};

// The actual data
typedef dense_hashtable<std::pair<const Key, T>, Key, HashFcn, SelectKey,
SetKey, EqualKey, Alloc> ht;
ht rep;

public:
typedef typename ht::key_type key_type;
typedef T data_type;
typedef T mapped_type;
typedef typename ht::value_type value_type;
typedef typename ht::hasher hasher;
typedef typename ht::key_equal key_equal;
typedef Alloc allocator_type;

typedef typename ht::size_type size_type;
typedef typename ht::difference_type difference_type;
typedef typename ht::pointer pointer;
typedef typename ht::const_pointer const_pointer;
typedef typename ht::reference reference;
typedef typename ht::const_reference const_reference;

typedef typename ht::iterator iterator;
typedef typename ht::const_iterator const_iterator;
typedef typename ht::local_iterator local_iterator;
typedef typename ht::const_local_iterator const_local_iterator;

// Iterator functions
iterator begin() { return rep.begin(); }
iterator end() { return rep.end(); }
const_iterator begin() const { return rep.begin(); }
const_iterator end() const { return rep.end(); }


// These come from tr1's unordered_map. For us, a bucket has 0 or 1 elements.
local_iterator begin(size_type i) { return rep.begin(i); }
local_iterator end(size_type i) { return rep.end(i); }
const_local_iterator begin(size_type i) const { return rep.begin(i); }
const_local_iterator end(size_type i) const { return rep.end(i); }

// Accessor functions
allocator_type get_allocator() const { return rep.get_allocator(); }
hasher hash_funct() const { return rep.hash_funct(); }
hasher hash_function() const { return hash_funct(); }
key_equal key_eq() const { return rep.key_eq(); }


// Constructors
explicit dense_hash_map(size_type expected_max_items_in_table = 0,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& alloc = allocator_type())
: rep(expected_max_items_in_table, hf, eql, SelectKey(), SetKey(), alloc) {
}

template <class InputIterator>
dense_hash_map(InputIterator f, InputIterator l,
const key_type& empty_key_val,
size_type expected_max_items_in_table = 0,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& alloc = allocator_type())
: rep(expected_max_items_in_table, hf, eql, SelectKey(), SetKey(), alloc) {
set_empty_key(empty_key_val);
rep.insert(f, l);
}
// We use the default copy constructor
// We use the default operator=()
// We use the default destructor

void clear() { rep.clear(); }
// This clears the hash map without resizing it down to the minimum
// bucket count, but rather keeps the number of buckets constant
void clear_no_resize() { rep.clear_no_resize(); }
void swap(dense_hash_map& hs) { rep.swap(hs.rep); }


// Functions concerning size
size_type size() const { return rep.size(); }
size_type max_size() const { return rep.max_size(); }
bool empty() const { return rep.empty(); }
size_type bucket_count() const { return rep.bucket_count(); }
size_type max_bucket_count() const { return rep.max_bucket_count(); }

// These are tr1 methods. bucket() is the bucket the key is or would be in.
size_type bucket_size(size_type i) const { return rep.bucket_size(i); }
size_type bucket(const key_type& key) const { return rep.bucket(key); }
float load_factor() const {
return size() * 1.0f / bucket_count();
}
float max_load_factor() const {
float shrink, grow;
rep.get_resizing_parameters(&shrink, &grow);
return grow;
}
void max_load_factor(float new_grow) {
float shrink, grow;
rep.get_resizing_parameters(&shrink, &grow);
rep.set_resizing_parameters(shrink, new_grow);
}
// These aren't tr1 methods but perhaps ought to be.
float min_load_factor() const {
float shrink, grow;
rep.get_resizing_parameters(&shrink, &grow);
return shrink;
}
void min_load_factor(float new_shrink) {
float shrink, grow;
rep.get_resizing_parameters(&shrink, &grow);
rep.set_resizing_parameters(new_shrink, grow);
}
// Deprecated; use min_load_factor() or max_load_factor() instead.
void set_resizing_parameters(float shrink, float grow) {
rep.set_resizing_parameters(shrink, grow);
}

void resize(size_type hint) { rep.resize(hint); }
void rehash(size_type hint) { resize(hint); } // the tr1 name

// Lookup routines
iterator find(const key_type& key) { return rep.find(key); }
const_iterator find(const key_type& key) const { return rep.find(key); }

data_type& operator[](const key_type& key) { // This is our value-add!
// If key is in the hashtable, returns find(key)->second,
// otherwise returns insert(value_type(key, T()).first->second.
// Note it does not create an empty T unless the find fails.
return rep.template find_or_insert<DefaultValue>(key).second;
}

size_type count(const key_type& key) const { return rep.count(key); }

std::pair<iterator, iterator> equal_range(const key_type& key) {
return rep.equal_range(key);
}
std::pair<const_iterator, const_iterator> equal_range(const key_type& key)
const {
return rep.equal_range(key);
}


// Insertion routines
std::pair<iterator, bool> insert(const value_type& obj) {
return rep.insert(obj);
}
template <class InputIterator> void insert(InputIterator f, InputIterator l) {
rep.insert(f, l);
}
void insert(const_iterator f, const_iterator l) {
rep.insert(f, l);
}
// Required for std::insert_iterator; the passed-in iterator is ignored.
iterator insert(iterator, const value_type& obj) {
return insert(obj).first;
}

// Deletion and empty routines
// THESE ARE NON-STANDARD! I make you specify an "impossible" key
// value to identify deleted and empty buckets. You can change the
// deleted key as time goes on, or get rid of it entirely to be insert-only.
void set_empty_key(const key_type& key) { // YOU MUST CALL THIS!
rep.set_empty_key(value_type(key, data_type())); // rep wants a value
}
key_type empty_key() const {
return rep.empty_key().first; // rep returns a value
}

void set_deleted_key(const key_type& key) { rep.set_deleted_key(key); }
void clear_deleted_key() { rep.clear_deleted_key(); }
key_type deleted_key() const { return rep.deleted_key(); }

// These are standard
size_type erase(const key_type& key) { return rep.erase(key); }
void erase(iterator it) { rep.erase(it); }
void erase(iterator f, iterator l) { rep.erase(f, l); }


// Comparison
bool operator==(const dense_hash_map& hs) const { return rep == hs.rep; }
bool operator!=(const dense_hash_map& hs) const { return rep != hs.rep; }


// I/O -- this is an add-on for writing hash map to disk
//
// For maximum flexibility, this does not assume a particular
// file type (though it will probably be a FILE *). We just pass
// the fp through to rep.

// If your keys and values are simple enough, you can pass this
// serializer to serialize()/unserialize(). "Simple enough" means
// value_type is a POD type that contains no pointers. Note,
// however, we don't try to normalize endianness.
typedef typename ht::NopointerSerializer NopointerSerializer;

// serializer: a class providing operator()(OUTPUT*, const value_type&)
// (writing value_type to OUTPUT). You can specify a
// NopointerSerializer object if appropriate (see above).
// fp: either a FILE*, OR an ostream*/subclass_of_ostream*, OR a
// pointer to a class providing size_t Write(const void*, size_t),
// which writes a buffer into a stream (which fp presumably
// owns) and returns the number of bytes successfully written.
// Note basic_ostream<not_char> is not currently supported.
template <typename ValueSerializer, typename OUTPUT>
bool serialize(ValueSerializer serializer, OUTPUT* fp) {
return rep.serialize(serializer, fp);
}

// serializer: a functor providing operator()(INPUT*, value_type*)
// (reading from INPUT and into value_type). You can specify a
// NopointerSerializer object if appropriate (see above).
// fp: either a FILE*, OR an istream*/subclass_of_istream*, OR a
// pointer to a class providing size_t Read(void*, size_t),
// which reads into a buffer from a stream (which fp presumably
// owns) and returns the number of bytes successfully read.
// Note basic_istream<not_char> is not currently supported.
// NOTE: Since value_type is std::pair<const Key, T>, ValueSerializer
// may need to do a const cast in order to fill in the key.
template <typename ValueSerializer, typename INPUT>
bool unserialize(ValueSerializer serializer, INPUT* fp) {
return rep.unserialize(serializer, fp);
}
};

// We need a global swap as well
template <class Key, class T, class HashFcn, class EqualKey, class Alloc>
inline void swap(dense_hash_map<Key, T, HashFcn, EqualKey, Alloc>& hm1,
dense_hash_map<Key, T, HashFcn, EqualKey, Alloc>& hm2) {
hm1.swap(hm2);
}

_END_GOOGLE_NAMESPACE_

#endif /* _DENSE_HASH_MAP_H_ */

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