path: root/common/hashmap.h

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// The hash map (associative array) implementation in this file is
// based on code by Andrew Y. Ng, 1996:

/*
 * Copyright (c) 1998-2003 Massachusetts Institute of Technology.
 * This code was developed as part of the Haystack research project
 * (http://haystack.lcs.mit.edu/). Permission is hereby granted,
 * free of charge, to any person obtaining a copy of this software
 * and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute,
 * sublicense, and/or sell copies of the Software, and to permit
 * persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef COMMON_HASHMAP_H
#define COMMON_HASHMAP_H

#include "common/func.h"
#include "common/str.h"
#include "common/util.h"

namespace Common {

// The table sizes ideally are primes. We use a helper function to find
// suitable table sizes.
uint nextTableSize(uint x);


// Enable the following #define if you want to check how many collisions the
// code produces (many collisions indicate either a bad hash function, or a
// hash table that is too small).
//#define DEBUG_HASH_COLLISIONS

/**
 * HashMap<Key,Val> maps objects of type Key to objects of type Val.
 * For each used Key type, we need an "uint hashit(Key,uint)" function
 * that computes a hash for the given Key object and returns it as an
 * an integer from 0 to hashsize-1, and also an "equality functor".
 * that returns true if if its two arguments are to be considered
 * equal. Also, we assume that "=" works on Val objects for assignment.
 *
 * If aa is an HashMap<Key,Val>, then space is allocated each time aa[key] is
 * referenced, for a new key. If the object is const, then an assertion is
 * triggered instead. Hence if you are not sure whether a key is contained in
 * the map, use contains() first to check for its presence.
 */
template <class Key, class Val, class HashFunc = Hash<Key>, class EqualFunc = EqualTo<Key> >
class HashMap {
private:
#if defined (PALMOS_MODE)
public:
#endif

	typedef HashMap<Key, Val, HashFunc, EqualFunc> HM_t;

	struct Node {
		const Key _key;
		Val _value;
		Node(const Key &key) : _key(key), _value() {}
	};

	Node **_arr;	// hashtable of size arrsize.
	uint _arrsize, _nele;

	HashFunc _hash;
	EqualFunc _equal;

	// Default value, returned by the const getVal.
	const Val _defaultVal;

#ifdef DEBUG_HASH_COLLISIONS
	mutable int _collisions, _lookups;
#endif

	void assign(const HM_t& map);
	int lookup(const Key &key) const;
	int lookupAndCreateIfMissing(const Key &key);
	void expand_array(uint newsize);

	/**
	 * Simple HashMap iterator implementation.
	 */
	class Iterator {
	protected:
		typedef const HashMap hashmap_t;
		friend class HashMap;

		// Allow ConstIterator to read member vars, so that Iterators can be converted to ConstIterator
		friend class HashMap::ConstIterator;

		uint _idx;
		hashmap_t *_hashmap;

	protected:
		Iterator(uint idx, hashmap_t *hashmap) : _idx(idx), _hashmap(hashmap) {}

		Node *deref() const {
			assert(_hashmap != 0);
			Node *node = _hashmap->_arr[_idx];
			assert(node != 0);
			return node;
		}

	public:
		Iterator() : _idx(0), _hashmap(0) {}

		Node &operator *() const { return *deref(); }
		Node *operator->() const { return deref(); }

		bool operator ==(const Iterator &iter) const { return _idx == iter._idx && _hashmap == iter._hashmap; }
		bool operator !=(const Iterator &iter) const { return !(*this == iter); }

		Iterator &operator ++() {
			assert(_hashmap);
			do {
				_idx++;
			} while (_idx < _hashmap->_arrsize && _hashmap->_arr[_idx] == 0);
			if (_idx >= _hashmap->_arrsize)
				_idx = (uint)-1;

			return *this;
		}

		Iterator operator ++(int) {
			Iterator old = *this;
			operator ++();
			return old;
		}
	};

	/**
	 * Simple HashMap const iterator implementation.
	 * This is almost completely identical to the normal iterator class, only
	 * with some const keywords added here and there, plus a conversion
	 * operator which makes it possible to transparently convert iterators to
	 * const iterators. 
	 * It is sadly not really possible to reduce this code duplication using
	 * template, unless one is willing to accept various warnings on certain
	 * compilers. Note that many (most? all?) implementations of the standard
	 * C++ library use a similar approach for their implementations.
	 */
	class ConstIterator {
	protected:
		typedef const HashMap hashmap_t;
		friend class HashMap;

		uint _idx;
		hashmap_t *_hashmap;

	protected:
		ConstIterator(uint idx, hashmap_t *hashmap) : _idx(idx), _hashmap(hashmap) {}

		const Node *deref() const {
			assert(_hashmap != 0);
			const Node *node = _hashmap->_arr[_idx];
			assert(node != 0);
			return node;
		}

	public:
		ConstIterator() : _idx(0), _hashmap(0) {}

		// Converting a non-const iterator to a const one is allowed
		ConstIterator(const Iterator &iter) : _idx(iter._idx), _hashmap(iter._hashmap) {}

		const Node &operator *() const { return *deref(); }
		const Node *operator->() const { return deref(); }

		bool operator ==(const ConstIterator &iter) const { return _idx == iter._idx && _hashmap == iter._hashmap; }
		bool operator !=(const ConstIterator &iter) const { return !(*this == iter); }

		ConstIterator &operator ++() {
			assert(_hashmap);
			do {
				_idx++;
			} while (_idx < _hashmap->_arrsize && _hashmap->_arr[_idx] == 0);
			if (_idx >= _hashmap->_arrsize)
				_idx = (uint)-1;

			return *this;
		}

		ConstIterator operator ++(int) {
			ConstIterator old = *this;
			operator ++();
			return old;
		}
	};

public:
	typedef Iterator iterator;
	typedef ConstIterator const_iterator;

	HashMap();
	HashMap(const HM_t& map);
	~HashMap();

	HM_t &operator =(const HM_t &map) {
		if (this == &map)
			return *this;

		// Remove the previous content and ...
		clear();
		delete[] _arr;
		// ... copy the new stuff.
		assign(map);
		return *this;
	}

	bool contains(const Key &key) const;

	Val &operator [](const Key &key);
	const Val &operator [](const Key &key) const;

	Val &getVal(const Key &key);
	const Val &getVal(const Key &key) const;
	void setVal(const Key &key, const Val &val);

	void clear(bool shrinkArray = 0);

	void erase(const Key &key);

	uint size() const { return _nele; }

	iterator	begin() {
		// Find and return the _key non-empty entry
		for (uint ctr = 0; ctr < _arrsize; ++ctr) {
			if (_arr[ctr])
				return iterator(ctr, this);
		}
		return end();
	}
	iterator	end() {
		return iterator((uint)-1, this);
	}

	const_iterator	begin() const {
		// Find and return the first non-empty entry
		for (uint ctr = 0; ctr < _arrsize; ++ctr) {
			if (_arr[ctr])
				return const_iterator(ctr, this);
		}
		return end();
	}
	const_iterator	end() const {
		return const_iterator((uint)-1, this);
	}

	iterator	find(const Key &key) {
		uint ctr = lookup(key);
		if (_arr[ctr])
			return iterator(ctr, this);
		return end();
	}

	const_iterator	find(const Key &key) const {
		uint ctr = lookup(key);
		if (_arr[ctr])
			return const_iterator(ctr, this);
		return end();
	}

	// TODO: insert() method?

	bool empty() const {
		return (_nele == 0);
	}
};

//-------------------------------------------------------
// HashMap functions

/**
 * Base constructor, creates an empty hashmap.
 */
template <class Key, class Val, class HashFunc, class EqualFunc>
HashMap<Key, Val, HashFunc, EqualFunc>::HashMap()
	: _defaultVal() {
	_arrsize = nextTableSize(0);
	_arr = new Node *[_arrsize];
	assert(_arr != NULL);
	memset(_arr, 0, _arrsize * sizeof(Node *));

	_nele = 0;

#ifdef DEBUG_HASH_COLLISIONS
	_collisions = 0;
	_lookups = 0;
#endif
}

/**
 * Copy constructor, creates a full copy of the given hashmap.
 * We must provide a custom copy constructor as we use pointers
 * to heap buffers for the internal storage.
 */
template <class Key, class Val, class HashFunc, class EqualFunc>
HashMap<Key, Val, HashFunc, EqualFunc>::HashMap(const HM_t& map)
	: _defaultVal()  {
	assign(map);
}

/**
 * Destructor, frees all used memory.
 */
template <class Key, class Val, class HashFunc, class EqualFunc>
HashMap<Key, Val, HashFunc, EqualFunc>::~HashMap() {
	for (uint ctr = 0; ctr < _arrsize; ++ctr)
		if (_arr[ctr] != NULL)
			delete _arr[ctr];

	delete[] _arr;
}

/**
 * Internal method for assigning the content of another HashMap
 * to this one.
 *
 * @note We do *not* deallocate the previous storage here -- the caller is
 *       responsible for doing that!
 */
template <class Key, class Val, class HashFunc, class EqualFunc>
void HashMap<Key, Val, HashFunc, EqualFunc>::assign(const HM_t& map) {
	_arrsize = map._arrsize;
	_arr = new Node *[_arrsize];
	assert(_arr != NULL);
	memset(_arr, 0, _arrsize * sizeof(Node *));

	// Simply clone the map given to us, one by one.
	_nele = 0;
	for (uint ctr = 0; ctr < _arrsize; ++ctr) {
		if (map._arr[ctr] != NULL) {
			_arr[ctr] = new Node(*map._arr[ctr]);
			_nele++;
		}
	}
	// Perform a sanity check (to help track down hashmap corruption)
	assert(_nele == map._nele);
}


template <class Key, class Val, class HashFunc, class EqualFunc>
void HashMap<Key, Val, HashFunc, EqualFunc>::clear(bool shrinkArray) {
	for (uint ctr = 0; ctr < _arrsize; ++ctr) {
		if (_arr[ctr] != NULL) {
			delete _arr[ctr];
			_arr[ctr] = NULL;
		}
	}

	if (shrinkArray && _arrsize > nextTableSize(0)) {
		delete[] _arr;

		_arrsize = nextTableSize(0);
		_arr = new Node *[_arrsize];
		assert(_arr != NULL);
		memset(_arr, 0, _arrsize * sizeof(Node *));
	}

	_nele = 0;
}

template <class Key, class Val, class HashFunc, class EqualFunc>
void HashMap<Key, Val, HashFunc, EqualFunc>::expand_array(uint newsize) {
	assert(newsize > _arrsize);
	uint ctr, dex;

	const uint old_nele = _nele;
	const uint old_arrsize = _arrsize;
	Node **old_arr = _arr;

	// allocate a new array
	_nele = 0;
	_arrsize = newsize;
	_arr = new Node *[_arrsize];
	assert(_arr != NULL);
	memset(_arr, 0, _arrsize * sizeof(Node *));

	// rehash all the old elements
	for (ctr = 0; ctr < old_arrsize; ++ctr) {
		if (old_arr[ctr] == NULL)
			continue;

		// Insert the element from the old table into the new table.
		// Since we know that no key exists twice in the old table, we
		// can do this slightly better than by calling lookup, since we
		// don't have to call _equal().
		dex = _hash(old_arr[ctr]->_key) % _arrsize;
		while (_arr[dex] != NULL) {
			dex = (dex + 1) % _arrsize;
		}

		_arr[dex] = old_arr[ctr];
		_nele++;
	}

	// Perform a sanity check: Old number of elements should match the new one!
	// This check will fail if some previous operation corrupted this hashmap.
	assert(_nele == old_nele);

	delete[] old_arr;

	return;
}

template <class Key, class Val, class HashFunc, class EqualFunc>
int HashMap<Key, Val, HashFunc, EqualFunc>::lookup(const Key &key) const {
	uint ctr = _hash(key) % _arrsize;

	while (_arr[ctr] != NULL && !_equal(_arr[ctr]->_key, key)) {
		ctr = (ctr + 1) % _arrsize;

#ifdef DEBUG_HASH_COLLISIONS
		_collisions++;
#endif
	}

#ifdef DEBUG_HASH_COLLISIONS
	_lookups++;
	fprintf(stderr, "collisions %d, lookups %d, ratio %f in HashMap %p; size %d num elements %d\n",
		_collisions, _lookups, ((double) _collisions / (double)_lookups),
		(const void *)this, _arrsize, _nele);
#endif

	return ctr;
}

template <class Key, class Val, class HashFunc, class EqualFunc>
int HashMap<Key, Val, HashFunc, EqualFunc>::lookupAndCreateIfMissing(const Key &key) {
	uint ctr = lookup(key);

	if (_arr[ctr] == NULL) {
		_arr[ctr] = new Node(key);
		_nele++;

		// Keep the load factor below 75%.
		if (_nele > _arrsize * 75 / 100) {
			expand_array(nextTableSize(_arrsize));
			ctr = lookup(key);
		}
	}

	return ctr;
}


template <class Key, class Val, class HashFunc, class EqualFunc>
bool HashMap<Key, Val, HashFunc, EqualFunc>::contains(const Key &key) const {
	uint ctr = lookup(key);
	return (_arr[ctr] != NULL);
}

template <class Key, class Val, class HashFunc, class EqualFunc>
Val &HashMap<Key, Val, HashFunc, EqualFunc>::operator [](const Key &key) {
	return getVal(key);
}

template <class Key, class Val, class HashFunc, class EqualFunc>
const Val &HashMap<Key, Val, HashFunc, EqualFunc>::operator [](const Key &key) const {
	return getVal(key);
}

template <class Key, class Val, class HashFunc, class EqualFunc>
Val &HashMap<Key, Val, HashFunc, EqualFunc>::getVal(const Key &key) {
	uint ctr = lookupAndCreateIfMissing(key);
	assert(_arr[ctr] != NULL);
	return _arr[ctr]->_value;
}

template <class Key, class Val, class HashFunc, class EqualFunc>
const Val &HashMap<Key, Val, HashFunc, EqualFunc>::getVal(const Key &key) const {
	uint ctr = lookup(key);
	if (_arr[ctr] != NULL)
		return _arr[ctr]->_value;
	else
		return _defaultVal;
}

template <class Key, class Val, class HashFunc, class EqualFunc>
void HashMap<Key, Val, HashFunc, EqualFunc>::setVal(const Key &key, const Val &val) {
	uint ctr = lookupAndCreateIfMissing(key);
	assert(_arr[ctr] != NULL);
	_arr[ctr]->_value = val;
}

template <class Key, class Val, class HashFunc, class EqualFunc>
void HashMap<Key, Val, HashFunc, EqualFunc>::erase(const Key &key) {
	// This is based on code in the Wikipedia article on Hash tables.
	uint i = lookup(key);
	if (_arr[i] == NULL)
		return; // key wasn't present, so no work has to be done
	// If we remove a key, we must check all subsequent keys and possibly
	// reinsert them.
	uint j = i;
	delete _arr[i];
	_arr[i] = NULL;
	while (true) {
		// Look at the next table slot
		j = (j + 1) % _arrsize;
		// If the next slot is empty, we are done
		if (_arr[j] == NULL)
			break;
		// Compute the slot where the content of the next slot should normally be,
		// assuming an empty table, and check whether we have to move it.
		uint k = _hash(_arr[j]->_key) % _arrsize;
		if ((j > i && (k <= i || k > j)) ||
		    (j < i && (k <= i && k > j)) ) {
			_arr[i] = _arr[j];
			i = j;
		}
	}
	_arr[i] = NULL;
	return;
}

}	// End of namespace Common

#endif