path: root/common/assocarray.h

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// Code is based on:

/* 
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/*************************************************

  assocarray.h - Associative arrays

  Andrew Y. Ng, 1996

**************************************************/

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

#ifndef COMMON_ASSOCARRAY_H
#define COMMON_ASSOCARRAY_H

namespace Common {

typedef Common::String String;

// If aa is an AssocArray<Key,Val>, then space is allocated each
// time aa[key] is referenced, for a new key. To "see" the value
// of aa[key] but without allocating new memory, use aa.queryVal(key)
// instead.
// 
// An AssocArray<Key,Val> Maps type Key to type Val. For each 
// Key, we need a int hashit(Key,int) that hashes Key and returns 
// an integer from 0 to hashsize-1, and a int data_eq(Key,Key) 
// that returns true if the 2 arguments it is passed are to
// be considered equal. Also, we assume that "=" works
// on Val's for assignment.

uint hashit(int x, uint hashsize);
bool data_eq(int x, int y);
uint hashit(double x, uint hashsize);
bool data_eq(double x, double y);
uint hashit(const char *str, uint hashsize);
bool data_eq(const char *str1, const char *str2);
uint hashit(const String &str, uint hashsize);
bool data_eq(const String &str1, const String &str2);


// 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

template <class Key, class Val>
class AssocArray {
private:
	// data structure used by AssocArray internally to keep
	// track of what's mapped to what.
	struct aa_ref_t {
		Key key;
		Val dat;
		aa_ref_t(const Key& k) : key(k) {}
	};
	
	aa_ref_t **_arr;	// hashtable of size arrsize.
	uint _arrsize, _nele;
	
#ifdef DEBUG_HASH_COLLISIONS
	mutable int _collisions, _lookups;
#endif

	int lookup(const Key &key) const;
	void expand_array(void);

public:

	AssocArray();
	~AssocArray();

	bool contains(const Key &key) const;

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

	void clear(bool shrinkArray = 0);

	// The following two methods are used to return a list of
	// all the keys / all the values (or rather, duplicates of them).
	// Currently they aren't used, and I think a better appraoch
	// is to add iterators, which allow the same in a more C++-style
	// fashion, do not require making duplicates, and finally
	// even allow in-place modifications of
	Key *new_all_keys(void) const;
	Val *new_all_values(void) const;
	//const_iterator	begin() const
	//const_iterator	end() const
	
	// TODO: There is no "remove" method yet.
	//void remove(const Key &key);


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

//-------------------------------------------------------
// AssocArray functions

template <class Key, class Val>
int AssocArray<Key, Val>::lookup(const Key &key) const {
	uint ctr = hashit(key, _arrsize);

	while (_arr[ctr] != NULL && !data_eq(_arr[ctr]->key, key)) {
		ctr++;
#ifdef DEBUG_HASH_COLLISIONS
		_collisions++;
#endif

		if (ctr == _arrsize)
			ctr = 0;
	}
	
#ifdef DEBUG_HASH_COLLISIONS
	_lookups++;
	fprintf(stderr, "collisions %d, lookups %d, ratio %f in AssocArray %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>
bool AssocArray<Key, Val>::contains(const Key &key) const {
	uint ctr = lookup(key);
	return (_arr[ctr] != NULL);
}

template <class Key, class Val>
Key *AssocArray<Key, Val>::new_all_keys(void) const {
	Key *all_keys;
	uint ctr, dex;

	if (_nele == 0)
		return NULL;

	all_keys = new Key[_nele];

	assert(all_keys != NULL);

	dex = 0;
	for (ctr = 0; ctr < _arrsize; ctr++) {
		if (_arr[ctr] == NULL)
			continue;
		all_keys[dex++] = _arr[ctr]->key;

		assert(dex <= _nele);
	}

	assert(dex == _nele);

	return all_keys;
}

template <class Key, class Val>
Val *AssocArray<Key, Val>::new_all_values(void) const {
	Val *all_values;
	uint ctr, dex;

	if (_nele == 0)
		return NULL;

	all_values = new Val[_nele];

	assert(all_values != NULL);

	dex = 0;
	for (ctr = 0; ctr < _arrsize; ctr++) {
		if (_arr[ctr] == NULL)
			continue;

		all_values[dex++] = _arr[ctr]->dat;

		assert(dex <= _nele);
	}

	assert(dex == _nele);

	return all_values;
}

template <class Key, class Val>
AssocArray<Key, Val>::AssocArray() {
	uint ctr;

	_arrsize = nextTableSize(0);
	_arr = new aa_ref_t *[_arrsize];
	assert(_arr != NULL);
	for (ctr = 0; ctr < _arrsize; ctr++)
		_arr[ctr] = NULL;

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

template <class Key, class Val>
AssocArray<Key, Val>::~AssocArray() {
	uint ctr;

	for (ctr = 0; ctr < _arrsize; ctr++)
		if (_arr[ctr] != NULL)
			delete _arr[ctr];

	delete[] _arr;
}

template <class Key, class Val>
void AssocArray<Key, Val>::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 aa_ref_t *[_arrsize];
		assert(_arr != NULL);
		for (uint ctr = 0; ctr < _arrsize; ctr++)
			_arr[ctr] = NULL;
	}

	_nele = 0;
}

template <class Key, class Val>
void AssocArray<Key, Val>::expand_array(void) {
	aa_ref_t **old_arr;
	uint old_arrsize, old_nele, ctr, dex;

	old_nele = _nele;
	old_arr = _arr;
	old_arrsize = _arrsize;

	// allocate a new array 
	_arrsize = nextTableSize(old_arrsize);
	_arr = new aa_ref_t *[_arrsize];

	assert(_arr != NULL);

	for (ctr = 0; ctr < _arrsize; ctr++)
		_arr[ctr] = NULL;

	_nele = 0;

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

//      (*this)[old_arr[ctr]->key] = old_arr[ctr]->dat;
		dex = hashit(old_arr[ctr]->key, _arrsize);

		while (_arr[dex] != NULL) {
			if (++dex == _arrsize)
				dex = 0;
		}

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

	assert(_nele == old_nele);

	delete[] old_arr;

	return;
}

template <class Key, class Val>
Val &AssocArray<Key, Val>::operator [](const Key &key) {
	uint ctr = lookup(key);

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

		// Only fill array to fifty percent
		if (_nele > _arrsize / 2) {
			expand_array();
			ctr = lookup(key);
		}
	}

	return _arr[ctr]->dat;
}

template <class Key, class Val>
const Val &AssocArray<Key, Val>::operator [](const Key &key) const {
	return queryVal(key);
}

template <class Key, class Val>
const Val &AssocArray<Key, Val>::queryVal(const Key &key) const {
	uint ctr = lookup(key);
	assert(_arr[ctr] != NULL);
	return _arr[ctr]->dat;
}

}	// End of namespace Common

#endif