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/********************************************************************* |
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* * |
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* Copyright (c) 1997,1998, 1999 * |
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* Multimedia DB Group and DEIS - CSITE-CNR, * |
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* University of Bologna, Bologna, ITALY. * |
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* * |
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* All Rights Reserved. * |
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* * |
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* Permission to use, copy, and distribute this software and its * |
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* documentation for NON-COMMERCIAL purposes and without fee is * |
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* hereby granted provided that this copyright notice appears in * |
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* all copies. * |
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* * |
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* THE AUTHORS MAKE NO REPRESENTATIONS OR WARRANTIES ABOUT THE * |
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* SUITABILITY OF THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING * |
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* BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, * |
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* FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. THE AUTHOR * |
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* SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A * |
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* RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS * |
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* DERIVATIVES. * |
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* * |
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*********************************************************************/ |
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|
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#include "MTcursor.h" |
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#include "MT.h" |
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#include "MTpredicate.h" |
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|
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class MTnode; |
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|
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int |
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sign(double x) |
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{ |
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if(x>0) return 1; |
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if(x<0) return -1; |
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return 0; |
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} |
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|
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int comparedst(dst *a, dst *b) { return sign(a->Bound()-b->Bound()); } |
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int comparedst(dst& a, dst& b) { return sign(a.Bound()-b.Bound()); } |
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int compareentry(MTentry *a, MTentry *b) { return sign(a->maxradius()-b->maxradius()); } |
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|
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MTcursor::MTcursor(const MT& tree, const MTpred& query): queue(comparedst), results(compareentry), tree(tree) |
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{ |
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GiSTpath path; |
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dst *d; |
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|
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path.MakeRoot(); |
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d=new dst(path, 0, MAXDOUBLE); |
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this->query=(MTpred *)query.Copy(); |
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queue.Insert(d); |
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} |
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|
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BOOL |
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MTcursor::IsReady() const |
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{ |
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if(queue.IsEmpty()) return (!results.IsEmpty()); |
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else if(results.IsEmpty()) return FALSE; |
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else return (queue.First()->Bound()>=results.First()->maxradius()); |
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} |
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|
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double |
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MTcursor::Bound() const |
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{ |
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if(queue.IsEmpty()) |
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if(results.IsEmpty()) return maxDist(); |
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else return(results.First()->maxradius()); |
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else if(results.IsEmpty()) return(queue.First()->Bound()); |
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else return MIN(queue.First()->Bound(), results.First()->maxradius()); |
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} |
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|
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void |
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MTcursor::FetchNode() |
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{ |
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if(queue.IsEmpty()) return; |
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|
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int i, iprev, inext; // these are the previous and the next entries to be examined |
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dst *d=queue.RemoveFirst(); |
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MTnode *node=(MTnode *)tree.ReadNode(d->Path()); // retrieve next node to be examined |
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|
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// cout << "Read node " << node->Path() << ": " << d->Bound() << endl; |
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// search the first children to be examined |
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for(unsigned int i=0; i<node->NumEntries(); i++) { // for each entry in the current node |
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MTentry *e=(MTentry *)((*node)[i].Ptr()); |
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double dist=query->distance(e->object()); |
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|
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if(!e->IsLeaf()) { // insert the child node in the priority queue |
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dst *dnew; |
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GiSTpath path=node->Path(); |
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double dmin=dist-e->maxradius(), dmax=dist+e->maxradius(); // these are lower- and upper-bounds on the distances of the descendants of the entry from the query object |
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|
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if(dmin<0) dmin=0; |
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path.MakeChild(e->Ptr()); |
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dnew=new dst(path, dmin, dist); |
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queue.Insert(dnew); |
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} |
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else { // insert the entry in the result list |
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MTentry *key=(MTentry *)e->Copy(); |
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|
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key->setminradius(0); |
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key->setmaxradius(dist); // we insert the actual distance from the query object as the key radius |
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results.Insert(key); |
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// cout << "Inserted (" << dist << ") into list in " << j <<"-th place\n"; |
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} |
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} |
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delete node; // delete examined node |
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delete d; |
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} |
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|
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MTentry * |
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MTcursor::Next() |
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{ |
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while(!IsReady()) FetchNode(); |
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if(!results.IsEmpty()) return results.RemoveFirst(); |
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else return NULL; |
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} |
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|
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MTcursor::~MTcursor() |
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{ |
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delete query; |
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while(!results.IsEmpty()) delete results.RemoveFirst(); |
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while(!queue.IsEmpty()) delete queue.RemoveFirst(); |
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} |
