433 lines
8.3 KiB
C++
433 lines
8.3 KiB
C++
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/*++
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Copyright (c) 1995 Microsoft Corporation
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Module Name:
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Table.cxx
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Abstract:
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Implementation of the CHashTable and CTableElement.
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Author:
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Mario Goertzel [MarioGo]
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Revision History:
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MarioGo 02-15-95 Bits 'n pieces
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MarioGo 12-18-95 Changed from UUID to generic object keys
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--*/
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#include<or.hxx>
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CTableElement *
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CTableElement::RemoveMatching(
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IN CTableKey &tk,
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OUT CTableElement **ppRemoved)
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/*++
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Routine Description:
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Helper function used to remove an element from a
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bucket in the hash table.
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Arguments:
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tk - Key to find the element being removed.
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ppRemoved - Contains the element removed or NULL upon return.
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Return Value:
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Pointer to the remaining elements in the list if any. Use
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to replace the current pointer in the bucket.
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--*/
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{
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CTableElement *pcurrent = this;
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CTableElement *psaved = 0;
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CTableElement *pfirst = this;
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while(pcurrent)
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{
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if (pcurrent->Compare(tk))
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{
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*ppRemoved = pcurrent;
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if (0 != psaved)
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{
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psaved->_pnext = pcurrent->_pnext;
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pcurrent->_pnext = 0;
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return(pfirst);
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}
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else
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{
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// removing the first element in the list
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ASSERT(pcurrent == pfirst);
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psaved = pcurrent->_pnext;
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pcurrent->_pnext = 0;
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return(psaved);
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}
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}
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psaved = pcurrent;
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pcurrent = pcurrent->_pnext;
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}
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*ppRemoved = 0;
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return(pfirst);
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}
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CTableElement *
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CTableElement::RemoveMatching(
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IN CTableElement *pte,
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OUT CTableElement **ppRemoved)
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/*++
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Routine Description:
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Helper function used to remove an element from a bucket in the hash table.
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Arguments:
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pte - Element to be removed, compared by pointer value.
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ppRemoved - Contains the element removed or NULL upon return.
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Return Value:
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Pointer to the remaining elements in the list if any. Use
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to replace the current pointer in the bucket.
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--*/
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{
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CTableElement *pcurrent = this;
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CTableElement *psaved = 0;
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CTableElement *pfirst = this;
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while(pcurrent)
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{
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if (pcurrent == pte)
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{
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*ppRemoved = pcurrent;
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if (0 != psaved)
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{
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psaved->_pnext = pcurrent->_pnext;
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pcurrent->_pnext = 0;
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return(pfirst);
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}
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else
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{
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// removing the first element in the list
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ASSERT(pcurrent == pfirst);
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psaved = pcurrent->_pnext;
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pcurrent->_pnext = 0;
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return(psaved);
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}
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}
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psaved = pcurrent;
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pcurrent = pcurrent->_pnext;
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}
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*ppRemoved = 0;
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return(pfirst);
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}
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CHashTable::CHashTable(ORSTATUS &status, UINT start_size)
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{
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_cBuckets = start_size;
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_cElements = 0;
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_last = 0;
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_buckets = new CTableElement *[start_size];
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if (0 == _buckets)
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{
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status = OR_NOMEM;
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return;
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}
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for(UINT i = 0; i < _cBuckets; i++)
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{
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_buckets[i] = NULL;
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}
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status = OR_OK;
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}
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CHashTable::~CHashTable()
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{
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#if 0
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#if DBG
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for(UINT i = 0; i < _cBuckets; i++)
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ASSERT(_buckets[i] == 0);
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#endif
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delete _buckets;
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#endif
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ASSERT(0); // D'tor unused 12/95
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}
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CTableElement *
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CHashTable::Lookup(
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IN CTableKey &id
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)
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{
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DWORD hash = id.Hash();
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CTableElement *it;
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it = _buckets[hash % _cBuckets];
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while(it)
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{
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if (it->Compare(id))
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{
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return(it);
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}
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it = it->Next();
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}
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return(0);
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}
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void
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CHashTable::Add(
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IN CTableElement *pElement
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)
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{
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DWORD hash = pElement->Hash();
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hash %= _cBuckets;
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_buckets[hash] = _buckets[hash]->Insert(pElement);
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_cElements++;
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if (_cElements > _cBuckets)
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{
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// Try to grow the table. If the allocation fails no need to worry,
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// everything still works but might be a bit slower.
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CTableElement **ppte = new CTableElement *[_cBuckets * 2];
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if (ppte)
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{
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UINT i, uiBucketsOld = _cBuckets;
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CTableElement *pteT1, *pteT2;
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CTableElement **ppteOld = _buckets;
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KdPrintEx((DPFLTR_DCOMSS_ID,
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DPFLTR_INFO_LEVEL,
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"OR: Growing table: %p\n",
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this));
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// Change to the larger array of buckets.
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_cBuckets *= 2;
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for(i = 0; i < _cBuckets; i++)
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{
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ppte[i] = NULL;
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}
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_buckets = ppte;
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// Move every element from the old table into the large table.
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for(i = 0; i < uiBucketsOld; i++)
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{
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pteT1 = ppteOld[i];
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while(pteT1)
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{
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pteT2 = pteT1->Next();
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pteT1->Unlink();
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// Same as calling Add() but don't update _cElements.
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hash = pteT1->Hash();
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hash %= _cBuckets;
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_buckets[hash] = _buckets[hash]->Insert(pteT1);
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pteT1 = pteT2;
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}
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}
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}
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}
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return;
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}
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CTableElement *
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CHashTable::Remove(
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IN CTableKey &id
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)
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/*++
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Routine Description:
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Looks up and removes an element from the table.
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Arguments:
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id - The key to match the element to be removed
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Return Value:
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NULL - The element was not in the table
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non-NULL - A pointer to the element which was removed.
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--*/
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{
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DWORD hash = id.Hash();
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CTableElement *pte;
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hash %= _cBuckets;
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_buckets[hash] = (_buckets[hash])->RemoveMatching(id, &pte);
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if (pte)
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{
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_cElements--;
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if (_last == pte)
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{
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_last = _buckets[hash];
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}
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}
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return pte;
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}
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void
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CHashTable::Remove(
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IN CTableElement *pElement
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)
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/*++
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Routine Description:
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Used to remove an element from the table given a pointer to it.
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Arguments:
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pElement - the element to be removed. This pointer value,
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keys are not compared.
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Return Value:
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None
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--*/
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{
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DWORD hash = pElement->Hash();
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CTableElement *pte;
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hash %= _cBuckets;
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_buckets[hash] = (_buckets[hash])->RemoveMatching(pElement, &pte);
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if (pte)
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{
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ASSERT(pte == pElement);
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_cElements--;
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if (_last == pElement)
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{
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_last = _buckets[hash];
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}
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}
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return;
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}
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CTableElement *
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CHashTable::Another(
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)
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/*++
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Routine Description:
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Returns an element from the table. Usually this will be
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element found after the element last returned from this
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function. It may, due to races not solved here, repeat
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an element or skip an element.
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Races occur when accessing the "_last" memeber; this
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function is called while holding a shared lock. (More
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then one thread may call it at a time.)
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This isn't as bad as it sounds. _last can only
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be set to null in Remove() which requires exclusive
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access.
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Arguments:
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None
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Return Value:
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NULL or a pointer to an element in the table.
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--*/
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{
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CTableElement *panother;
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int i, end;
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if (_cElements == 0)
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{
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return(0);
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}
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if (_last)
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{
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if (panother = _last->Next())
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{
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if (panother)
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{
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_last = panother;
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return(panother);
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}
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}
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ASSERT(panother == 0);
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// no next, start looking from just after last's hash.
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i = _last->Hash();
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// Exersise for the reader (x + y) mod n == ( x mod n + y mod n ) mod n
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end = i = (i + 1) % _cBuckets;
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}
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else
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{
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// no last, start from the start.
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i = 0;
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end = _cBuckets - 1;
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}
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do
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{
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if (_buckets[i])
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{
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panother = _buckets[i];
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ASSERT(panother);
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_last = panother;
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return(panother);
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}
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i = (i + 1) % _cBuckets;
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}
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while (i != end);
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// Doesn't mean the table is empty, just that we didn't find
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// another element. These are not the same thing.
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return(0);
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}
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