kernel/util/OpenHashTable.h

/*
 * Copyright 2007, Hugo Santos. All Rights Reserved.
 * Distributed under the terms of the MIT License.
 */
#ifndef _KERNEL_UTIL_OPEN_HASH_TABLE_H
#define _KERNEL_UTIL_OPEN_HASH_TABLE_H


#include <OS.h>
#include <stdlib.h>
#include <string.h>

#ifdef _KERNEL_MODE
#	include <KernelExport.h>
#	include <util/kernel_cpp.h>
#endif


/*!
	The Definition template must have four methods: `HashKey', `Hash',
	`Compare' and `GetLink;. It must also define several types as shown in the
	following example:

	struct Foo : HashTableLink<Foo> {
		int bar;

		HashTableLink<Foo> otherLink;
	};

	struct HashTableDefinition {
		typedef int		KeyType;
		typedef	Foo		ValueType;

		HashTableDefinition(const HashTableDefinition&) {}

		size_t HashKey(int key) const { return key >> 1; }
		size_t Hash(Foo *value) const { return HashKey(value->bar); }
		bool Compare(int key, Foo *value) const { return value->bar == key; }
		HashTableLink<Foo> *GetLink(Foo *value) const { return value; }
	};
*/

template<typename Type>
struct HashTableLink {
	Type *fNext;
};

template<typename Definition, bool AutoExpand = true,
	bool CheckDuplicates = false>
class OpenHashTable {
public:
	typedef OpenHashTable<Definition, AutoExpand, CheckDuplicates> HashTable;
	typedef typename Definition::KeyType	KeyType;
	typedef typename Definition::ValueType	ValueType;

	static const size_t kMinimumSize = 8;

	// we use malloc() / free() for allocation. If in the future this
	// is revealed to be insufficient we can switch to a template based
	// allocator. All allocations are of power of 2 lengths.

	// regrowth factor: 200 / 256 = 78.125%
	//                   50 / 256 = 19.53125%

	OpenHashTable()
		:
		fTableSize(0),
		fItemCount(0),
		fTable(NULL)
	{
	}

	OpenHashTable(const Definition& definition)
		:
		fDefinition(definition),
		fTableSize(0),
		fItemCount(0),
		fTable(NULL)
	{
	}

	~OpenHashTable()
	{
		free(fTable);
	}

	status_t Init(size_t initialSize = kMinimumSize)
	{
		if (initialSize > 0 && !_Resize(initialSize))
			return B_NO_MEMORY;
		return B_OK;
	}

	size_t TableSize() const
	{
		return fTableSize;
	}

	size_t CountElements() const
	{
		return fItemCount;
	}

	ValueType *Lookup(const KeyType &key) const
	{
		if (fTableSize == 0)
			return NULL;

		size_t index = fDefinition.HashKey(key) & (fTableSize - 1);
		ValueType *slot = fTable[index];

		while (slot) {
			if (fDefinition.Compare(key, slot))
				break;
			slot = _Link(slot)->fNext;
		}

		return slot;
	}

	status_t Insert(ValueType *value)
	{
		if (fTableSize == 0) {
			if (!_Resize(kMinimumSize))
				return B_NO_MEMORY;
		} else if (AutoExpand && fItemCount >= (fTableSize * 200 / 256))
			_Resize(fTableSize * 2);

		InsertUnchecked(value);
		return B_OK;
	}

	void InsertUnchecked(ValueType *value)
	{
		if (CheckDuplicates && _ExhaustiveSearch(value)) {
#ifdef _KERNEL_MODE
			panic("Hash Table: value already in table.");
#else
			debugger("Hash Table: value already in table.");
#endif
		}

		_Insert(fTable, fTableSize, value);
		fItemCount++;
	}

	// TODO: a ValueType* Remove(const KeyType& key) method is missing

	bool Remove(ValueType *value)
	{
		if (!RemoveUnchecked(value))
			return false;

		if (AutoExpand && fTableSize > kMinimumSize
			&& fItemCount < (fTableSize * 50 / 256))
			_Resize(fTableSize / 2);

		return true;
	}

	bool RemoveUnchecked(ValueType *value)
	{
		size_t index = fDefinition.Hash(value) & (fTableSize - 1);
		ValueType *previous = NULL, *slot = fTable[index];

		while (slot) {
			ValueType *next = _Link(slot)->fNext;

			if (value == slot) {
				if (previous)
					_Link(previous)->fNext = next;
				else
					fTable[index] = next;
				break;
			}

			previous = slot;
			slot = next;
		}

		if (slot == NULL)
			return false;

		if (CheckDuplicates && _ExhaustiveSearch(value)) {
#ifdef _KERNEL_MODE
			panic("Hash Table: duplicate detected.");
#else
			debugger("Hash Table: duplicate detected.");
#endif
		}

		fItemCount--;
		return true;
	}

	/*!	Removes all elements from the hash table. No resizing happens. The
		elements are not deleted. If \a returnElements is \c true, the method
		returns all elements chained via their hash table link.
	*/
	ValueType* Clear(bool returnElements = false)
	{
		if (this->fItemCount == 0)
			return NULL;

		ValueType* result = NULL;

		if (returnElements) {
			ValueType** nextPointer = &result;

			// iterate through all buckets
			for (size_t i = 0; i < fTableSize; i++) {
				ValueType* element = fTable[i];
				if (element != NULL) {
					// add the bucket to the list
					*nextPointer = element;

					// update nextPointer to point to the fNext of the last
					// element in the bucket
					while (element != NULL) {
						nextPointer = &_Link(element)->fNext;
						element = *nextPointer;
					}
				}
			}
		}

		memset(this->fTable, 0, sizeof(ValueType*) * this->fTableSize);

		return result;
	}

	/*!	If the table needs resizing, the number of bytes for the required
		allocation is returned. If no resizing is needed, 0 is returned.
	*/
	size_t ResizeNeeded() const
	{
		size_t size = fTableSize;
		if (size == 0 || fItemCount >= (size * 200 / 256)) {
			// grow table
			if (size == 0)
				size = kMinimumSize;
			while (fItemCount >= size * 200 / 256)
				size <<= 1;
		} else if (size > kMinimumSize && fItemCount < size * 50 / 256) {
			// shrink table
			while (fItemCount < size * 50 / 256)
				size >>= 1;
			if (size < kMinimumSize)
				size = kMinimumSize;
		}

		if (size == fTableSize)
			return 0;

		return size * sizeof(ValueType*);
	}

	/*!	Resizes the table using the given allocation. The allocation must not
		be \c NULL. It must be of size \a size, which must a value returned
		earlier by ResizeNeeded(). If the size requirements have changed in the
		meantime, the method free()s the given allocation and returns \c false.
		Otherwise \c true is returned.
	*/
	bool Resize(void* allocation, size_t size)
	{
		if (size != ResizeNeeded()) {
			free(allocation);
			return false;
		}

		_Resize((ValueType**)allocation, size / sizeof(ValueType*));
		return true;
	}

	class Iterator {
	public:
		Iterator(const HashTable *table)
			: fTable(table)
		{
			Rewind();
		}

		Iterator(const HashTable *table, size_t index, ValueType *value)
			: fTable(table), fIndex(index), fNext(value) {}

		bool HasNext() const { return fNext != NULL; }

		ValueType *Next()
		{
			ValueType *current = fNext;
			_GetNext();
			return current;
		}

		void Rewind()
		{
			// get the first one
			fIndex = 0;
			fNext = NULL;
			_GetNext();
		}

	protected:
		Iterator() {}

		void _GetNext()
		{
			if (fNext)
				fNext = fTable->_Link(fNext)->fNext;

			while (fNext == NULL && fIndex < fTable->fTableSize)
				fNext = fTable->fTable[fIndex++];
		}

		const HashTable *fTable;
		size_t fIndex;
		ValueType *fNext;
	};

	Iterator GetIterator() const { return Iterator(this); }

protected:
	// for g++ 2.95
	friend class Iterator;

	void _Insert(ValueType **table, size_t tableSize, ValueType *value)
	{
		size_t index = fDefinition.Hash(value) & (tableSize - 1);

		_Link(value)->fNext = table[index];
		table[index] = value;
	}

	bool _Resize(size_t newSize)
	{
		ValueType** newTable
			= (ValueType**)malloc(sizeof(ValueType*) * newSize);
		if (newTable == NULL)
			return false;

		_Resize(newTable, newSize);
		return true;
	}

	void _Resize(ValueType** newTable, size_t newSize)
	{
		for (size_t i = 0; i < newSize; i++)
			newTable[i] = NULL;

		if (fTable) {
			for (size_t i = 0; i < fTableSize; i++) {
				ValueType *bucket = fTable[i];
				while (bucket) {
					ValueType *next = _Link(bucket)->fNext;
					_Insert(newTable, newSize, bucket);
					bucket = next;
				}
			}

			free(fTable);
		}

		fTableSize = newSize;
		fTable = newTable;
	}

	HashTableLink<ValueType> *_Link(ValueType *bucket) const
	{
		return fDefinition.GetLink(bucket);
	}

	bool _ExhaustiveSearch(ValueType *value) const
	{
		for (size_t i = 0; i < fTableSize; i++) {
			ValueType *bucket = fTable[i];
			while (bucket) {
				if (bucket == value)
					return true;
				bucket = _Link(bucket)->fNext;
			}
		}

		return false;
	}

	Definition fDefinition;
	size_t fTableSize, fItemCount;
	ValueType **fTable;
};

#endif	// _KERNEL_UTIL_OPEN_HASH_TABLE_H