DOMNodeIDMap.cpp

/*
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 * individuals on behalf of the Apache Software Foundation, and was
 * originally based on software copyright (c) 2001, International
 * Business Machines, Inc., http://www.ibm.com .  For more information
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 * <http://www.apache.org/>.
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/*
 * $Id$
 */

#include "DOMAttrImpl.hpp"
#include "DOMDocumentImpl.hpp"
#include "DOMNodeIDMap.hpp"

#include <xercesc/util/XMLString.hpp>
#include <xercesc/util/RuntimeException.hpp>
#include <stdio.h>

static const int gPrimes[] = {997, 9973, 99991, 999983, 0 };  // To do - add a few more.

static const float gMaxFill = 0.8f;   // The maximum fraction of the total
                                    // table entries to consume before exanding.

DOMNodeIDMap::DOMNodeIDMap(int initialSize, DOMDocument *doc)
{
    fDoc = doc;

    for (fSizeIndex = 0; gPrimes[fSizeIndex] < initialSize; fSizeIndex++)
    {
        if (gPrimes[fSizeIndex] == 0)
        {
            // We need a bigger size than the largest available one.
            //   Big trouble.
            fSizeIndex--;
            ThrowXML(RuntimeException, XMLExcepts::NodeIDMap_GrowErr);
        }
    }

    fSize = gPrimes[fSizeIndex];
    fNumEntries = 0;
    fMaxEntries = (XMLSize_t)(float(fSize) * gMaxFill);

    //fTable = new (fDoc) DOMAttr*[fSize];
    fTable = (DOMAttr**) ((DOMDocumentImpl *)fDoc)->allocate(sizeof(DOMAttr*) * fSize);
    XMLSize_t i;
    for (i=0; i<fSize; i++)
        fTable[i] = 0;
};


DOMNodeIDMap::~DOMNodeIDMap()
{
    // don't delete - the document owns the storage.
    fTable = 0;
};



void DOMNodeIDMap::add(DOMAttr *attr)
{
	//
	//  If the table is getting too full, grow it.  We arbitrarily limit
	//   the table to 80 full, which should limit the average number of
	//   rehashes to a reasonable value.
	//
	if (fNumEntries >= fMaxEntries)
		growTable();
    fNumEntries++;

	//
	// Hash the value string from the ID attribute being added to the table
	//      0 < Initial hash value < table size.
	//      An initial hash of zero would cause the rehash to fail.
	//
	const XMLCh *id=attr->getValue();
    XMLSize_t initalHash = XMLString::hash(id, fSize-1);
	initalHash++;
	XMLSize_t currentHash = initalHash;

	//
	// Loop looking for an empty slot for this ID.
	//   Don't even bother checking to see if the ID is already there -
	//   the table is only filled by the parser from valid documents, which
	//   can not have duplicates.  Behavior of invalid docs is not defined.
	//
    while (true)
	{
		DOMAttr *tableSlot = fTable[currentHash];
		if (tableSlot == 0 ||
			tableSlot == (DOMAttr *)-1)
			break;
		currentHash += initalHash;  // rehash
        if (currentHash >= fSize)
            currentHash = currentHash % fSize;
    }

    //
    // We've found our slot.  Stick the pointer to the attr into it.
    //
    fTable[currentHash] = attr;

};


void DOMNodeIDMap::remove(DOMAttr *attr)
{
    //
	// Hash the value string from the ID attribute being added to the table
	//      0 < Initial hash value < table size.
	//      An initial hash of zero would cause the rehash to fail.
	//
	const XMLCh *id=attr->getValue();
    XMLSize_t initalHash = XMLString::hash(id, fSize-1);
	initalHash++;
	XMLSize_t currentHash = initalHash;

	//
	// Loop looking for a slot pointing to an attr with this id.
    //
    while (true)
	{
		DOMAttr *tableSlot = fTable[currentHash];
		if (tableSlot == 0)
        {
            // There is no matching entry in the table
            return;
        }

        if (tableSlot == attr)
        {
            //  Found the attribute.  Set the slot to -1 to indicate
            //   that it was once used, meaning that lookups, while never
            //   matching here, can not stop either, but must rehash again
            //   and continue searching.
            fTable[currentHash] = (DOMAttr *)-1;
            return;
        }

        currentHash += initalHash;  // rehash.
        if (currentHash >= fSize)
            currentHash = currentHash % fSize;
    }

};


DOMAttr *DOMNodeIDMap::find(const XMLCh *id)
{
    //
    //  Get the hashcode for the supplied string.
    //
	XMLSize_t initalHash = XMLString::hash(id, fSize-1);
	initalHash++;
	XMLSize_t currentHash = initalHash;

	//
	// Loop looking for a slot pointing to an attr with this id.
    //
    while (true)
	{
		DOMAttr *tableSlot = fTable[currentHash];
		if (tableSlot == 0)
        {
            // There is no matching entry in the table
            return 0;
        }


        if ((tableSlot != (DOMAttr *)-1) && XMLString::compareString(tableSlot->getValue(), id) == 0)
            return tableSlot;

        currentHash += initalHash;  // rehash
        if (currentHash >= fSize)
            currentHash = currentHash % fSize;
    }
    return 0;  // Never gets here, but keeps some compilers happy.
};


//
//  Grow the table to the next larger size.
//      It has gotten too full for efficient operation.
//     (We never fill it all the way)
//
void DOMNodeIDMap::growTable()
{
    DOMAttr     **oldTable = fTable;
    XMLSize_t oldSize  = fSize;

    //
    //  Figure the new table size.
    //
#if defined(XERCES_DEBUG)
    fprintf(stderr, "growing...\n");
#endif
    fSizeIndex++;
    fSize = gPrimes[fSizeIndex];
    if (fSize == 0)
    {
        // We need to grow bigger than the largest available size.
        //   Big trouble.
        fSizeIndex--;
        ThrowXML(RuntimeException, XMLExcepts::NodeIDMap_GrowErr);
    }

    //
    //  Allocate the new table.
    //
    //fTable = new (fDoc) DOMAttr *[fSize];
    fTable = (DOMAttr**) ((DOMDocumentImpl *)fDoc)->allocate(sizeof(DOMAttr*) * fSize);
    XMLSize_t i;
    for (i=0; i<fSize; i++)
        fTable[i] = 0;

    fMaxEntries = (XMLSize_t)(float(fSize) * gMaxFill);

    //
    // Move entries over from the old table to the new one.
    //
    for (i=0; i<oldSize; i++)
    {
        if ((oldTable[i] != 0)  &&  (oldTable[i] != (DOMAttr *)-1))
            add(oldTable[i]);
    }

    // delete [] oldTable;   (The document owns the storage.  The old table will just
    //                        need to leak until until the document is discarded.)

};