haiku/headers/private/shared/OpenHashTable.h

/*
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*/

// bonefish:
// * removed need for exceptions
// * fixed warnings
// * implemented rehashing
// * added RemoveAll()
// TODO:
// * shrinking of element vectors

// Hash table with open addresssing

#ifndef __OPEN_HASH_TABLE__
#define __OPEN_HASH_TABLE__

#include <malloc.h>
#include <new>

// don't include <Debug.h>
#define ASSERT(E)               (void)0
#define TRESPASS()              (void)0
 
namespace BPrivate {

template <class Element>
class ElementVector {
	// element vector for OpenHashTable needs to implement this
	// interface
public:
	Element &At(int32 index);
	Element *Add();
	int32 IndexOf(const Element &) const;
	void Remove(int32 index);
};

class OpenHashElement {
public:
	uint32 Hash() const;
	bool operator==(const OpenHashElement &) const;
	void Adopt(OpenHashElement &);
		// low overhead copy, original element is in undefined state
		// after call (calls Adopt on BString members, etc.)
	int32 fNext;
};

const uint32 kPrimes [] = {
	509, 1021, 2039, 4093, 8191, 16381, 32749, 65521, 131071, 262139,
	524287, 1048573, 2097143, 4194301, 8388593, 16777213, 33554393, 67108859,
	134217689, 268435399, 536870909, 1073741789, 2147483647, 0
};

template <class Element, class ElementVec = ElementVector<Element> >
class OpenHashTable {
public:
	OpenHashTable(int32 minSize, ElementVec *elementVector = 0,
				  float maxLoadFactor = 0.8);
		// it is up to the subclass of OpenHashTable to supply
		// elementVector
	~OpenHashTable();
	
	bool InitCheck() const;

	void SetElementVector(ElementVec *elementVector);
	
	Element *FindFirst(uint32 elementHash) const;
	Element *Add(uint32 elementHash);
	
	void Remove(Element *element, bool dontRehash = false);
	void RemoveAll();
	
	// when calling Add, any outstanding element pointer may become
	// invalid; to deal with this, get the element index and restore
	// it after the add
	int32 ElementIndex(const Element *) const;
	Element *ElementAt(int32 index) const;

	int32 ArraySize() const;
	int32 VectorSize() const;
	int32 CountElements() const;

protected:
	static int32 OptimalSize(int32 minSize);

private:
	bool _RehashIfNeeded();
	bool _Rehash();
	
	int32 fArraySize;
	int32 fInitialSize;
	int32 fElementCount;
	int32 *fHashArray;
	ElementVec *fElementVector;
	float fMaxLoadFactor;
};

template <class Element>
class OpenHashElementArray : public ElementVector<Element> {
	// this is a straightforward implementation of an element vector
	// deleting is handled by linking deleted elements into a free list
	// the vector never shrinks
public:
	OpenHashElementArray(int32 initialSize);
	~OpenHashElementArray();

	bool InitCheck() const;

	Element &At(int32 index);
	const Element &At(int32 index) const;
	Element *Add(const Element &);
	Element *Add();
	void Remove(int32 index);
	int32 IndexOf(const Element &) const;
	int32 Size() const;

private:
	Element *fData;
	int32 fSize;
	int32 fNextFree;
	int32 fNextDeleted;
};


//-----------------------------------

template<class Element, class ElementVec>
OpenHashTable<Element, ElementVec>::OpenHashTable(int32 minSize,
	ElementVec *elementVector, float maxLoadFactor)
	:	fArraySize(OptimalSize(minSize)),
		fInitialSize(fArraySize),
		fElementCount(0),
		fElementVector(elementVector),
		fMaxLoadFactor(maxLoadFactor)
{
	// sanity check the maximal load factor
	if (fMaxLoadFactor < 0.5)
		fMaxLoadFactor = 0.5;
	// allocate and init the array
	fHashArray = (int32*)calloc(fArraySize, sizeof(int32));
	if (fHashArray) {
		for (int32 index = 0; index < fArraySize; index++)
			fHashArray[index] = -1;
	}
}

template<class Element, class ElementVec>
OpenHashTable<Element, ElementVec>::~OpenHashTable()
{
	RemoveAll();
	free(fHashArray);
}

template<class Element, class ElementVec>
bool
OpenHashTable<Element, ElementVec>::InitCheck() const
{
	return (fHashArray && fElementVector);
}

template<class Element, class ElementVec>
int32 
OpenHashTable<Element, ElementVec>::OptimalSize(int32 minSize)
{
	for (int32 index = 0; ; index++)
		if (!kPrimes[index] || kPrimes[index] >= (uint32)minSize)
			return (int32)kPrimes[index];

	return 0;
}

template<class Element, class ElementVec>
Element *
OpenHashTable<Element, ElementVec>::FindFirst(uint32 hash) const
{
	ASSERT(fElementVector);
	hash %= fArraySize;
	if (fHashArray[hash] < 0)
		return 0;
	
	return &fElementVector->At(fHashArray[hash]);
}

template<class Element, class ElementVec>
int32 
OpenHashTable<Element, ElementVec>::ElementIndex(const Element *element) const
{
	return fElementVector->IndexOf(*element);
}

template<class Element, class ElementVec>
Element *
OpenHashTable<Element, ElementVec>::ElementAt(int32 index) const
{
	return &fElementVector->At(index);
}

template<class Element, class ElementVec>
int32 
OpenHashTable<Element, ElementVec>::ArraySize() const
{
	 return fArraySize;
}

template<class Element, class ElementVec>
int32 
OpenHashTable<Element, ElementVec>::VectorSize() const
{
	 return fElementVector->Size();
}

template<class Element, class ElementVec>
int32 
OpenHashTable<Element, ElementVec>::CountElements() const
{
	 return fElementCount;
}


template<class Element, class ElementVec>
Element *
OpenHashTable<Element, ElementVec>::Add(uint32 hash)
{
	ASSERT(fElementVector);
	_RehashIfNeeded();
	hash %= fArraySize;
	Element *result = fElementVector->Add();
	if (result) {
		result->fNext = fHashArray[hash];
		fHashArray[hash] = fElementVector->IndexOf(*result);
		fElementCount++;
	}
	return result;
}

template<class Element, class ElementVec>
void 
OpenHashTable<Element, ElementVec>::Remove(Element *element, bool dontRehash)
{
	if (!dontRehash)
		_RehashIfNeeded();
	uint32 hash = element->Hash() % fArraySize;
	int32 next = fHashArray[hash];
	ASSERT(next >= 0);

	if (&fElementVector->At(next) == element) {
		fHashArray[hash] = element->fNext;
		fElementVector->Remove(next);
		fElementCount--;
		return;
	}

	for (int32 index = next; index >= 0; ) {
		// look for an existing match in table
		next = fElementVector->At(index).fNext;
		if (next < 0) {
			TRESPASS();
			return;
		}
		
		if (&fElementVector->At(next) == element) {
			fElementVector->At(index).fNext = element->fNext;
			fElementVector->Remove(next);
			fElementCount--;
			return;
		}
		index = next;
	}
}

template<class Element, class ElementVec>
void 
OpenHashTable<Element, ElementVec>::RemoveAll()
{
	for (int32 i = 0; fElementCount > 0 && i < fArraySize; i++) {
		int32 index = fHashArray[i];
		while (index >= 0) {
			Element* element = &fElementVector->At(index);
			int32 next = element->fNext;
			fElementVector->Remove(index);
			fElementCount--;
			index = next;
		}
		fHashArray[i] = -1;
	}
	_RehashIfNeeded();
}

template<class Element, class ElementVec>
void 
OpenHashTable<Element, ElementVec>::SetElementVector(ElementVec *elementVector)
{
	fElementVector = elementVector;
}

// _RehashIfNeeded
template<class Element, class ElementVec>
bool
OpenHashTable<Element, ElementVec>::_RehashIfNeeded()
{
	// The load factor range [fMaxLoadFactor / 3, fMaxLoadFactor] is fine,
	// I think. After rehashing the load factor will be about
	// fMaxLoadFactor * 2 / 3, respectively fMaxLoadFactor / 2.
	float loadFactor = (float)fElementCount / (float)fArraySize;
	if (loadFactor > fMaxLoadFactor
		|| (fArraySize > fInitialSize && loadFactor < fMaxLoadFactor / 3)) {
		return _Rehash();
	}
	return true;
}

// _Rehash
template<class Element, class ElementVec>
bool
OpenHashTable<Element, ElementVec>::_Rehash()
{
	bool result = true;
	int32 newSize = int32(fElementCount * 1.73 * fMaxLoadFactor);
	newSize = (fInitialSize > newSize ? fInitialSize : newSize);
	if (newSize != fArraySize) {
		// allocate a new array
		int32 *newHashArray = (int32*)calloc(newSize, sizeof(int32));
		if (newHashArray) {
			// init the new hash array
			for (int32 index = 0; index < newSize; index++)
				newHashArray[index] = -1;
			// iterate through all elements and put them into the new
			// hash array
			for (int i = 0; i < fArraySize; i++) {
				int32 index = fHashArray[i];
				while (index >= 0) {
					// insert the element in the new array
					Element &element = fElementVector->At(index);
					int32 next = element.fNext;
					uint32 hash = (element.Hash() % newSize);
					element.fNext = newHashArray[hash];
					newHashArray[hash] = index;
					// next element in old list
					index = next;
				}
			}
			// delete the old array and set the new one
			free(fHashArray);
			fHashArray = newHashArray;
			fArraySize = newSize;
		} else
			result = false;
	}
	return result;
}


template<class Element>
OpenHashElementArray<Element>::OpenHashElementArray(int32 initialSize)
	:	fSize(initialSize),
		fNextFree(0),
		fNextDeleted(-1)
{
	fData = (Element*)calloc((size_t)initialSize, sizeof(Element));
}

template<class Element>
OpenHashElementArray<Element>::~OpenHashElementArray()
{
	free(fData);
}

template<class Element>
bool
OpenHashElementArray<Element>::InitCheck() const
{
	return fData;
}

template<class Element>
Element &
OpenHashElementArray<Element>::At(int32 index)
{
	ASSERT(index < fSize);
	return fData[index];
}

template<class Element>
const Element &
OpenHashElementArray<Element>::At(int32 index) const
{
	ASSERT(index < fSize);
	return fData[index];
}

template<class Element>
int32 
OpenHashElementArray<Element>::IndexOf(const Element &element) const
{
	int32 result = &element - fData;
	if (result < 0 || result > fSize)
		return -1;
	
	return result;
}

template<class Element>
int32 
OpenHashElementArray<Element>::Size() const
{
	return fSize;
}


template<class Element>
Element *
OpenHashElementArray<Element>::Add(const Element &newElement)
{
	Element *element = Add();
	if (element)
		element.Adopt(newElement);
	return element;
}

#if DEBUG
const int32 kGrowChunk = 10;
#else
const int32 kGrowChunk = 1024;
#endif

template<class Element>
Element *
OpenHashElementArray<Element>::Add()
{
	int32 index = fNextFree;
	if (fNextDeleted >= 0) {
		index = fNextDeleted;
		fNextDeleted = At(index).fNext;		
	} else if (fNextFree >= fSize - 1) {
		int32 newSize = fSize + kGrowChunk;
/*
		Element *newData = (Element *)calloc((size_t)newSize , sizeof(Element));
		if (!newData)
			return NULL;
		memcpy(newData, fData, fSize * sizeof(Element));
		free(fData);
*/
		Element *newData = (Element*)realloc(fData,
			(size_t)newSize * sizeof(Element));
		if (!newData)
			return NULL;

		fData = newData;
		fSize = newSize;
		index = fNextFree;
		fNextFree++;
	} else
		fNextFree++;

	new (&At(index)) Element;
		// call placement new to initialize the element properly
	ASSERT(At(index).fNext == -1);

	return &At(index);		
}

template<class Element>
void 
OpenHashElementArray<Element>::Remove(int32 index)
{
	// delete by chaining empty elements in a single linked
	// list, reusing the next field
	ASSERT(index < fSize);
	At(index).~Element();
		// call the destructor explicitly to destroy the element
		// properly
	At(index).fNext = fNextDeleted;
	fNextDeleted = index;
}

} // namespace BPrivate

using BPrivate::OpenHashTable;

#endif // __OPEN_HASH_TABLE__