326 lines
8.6 KiB
C++
326 lines
8.6 KiB
C++
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//+---------------------------------------------------------------------------
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//
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// Microsoft Windows
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// Copyright (C) Microsoft Corporation, 1996-2000
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//
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// File: CHash.hxx
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//
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// Contents: Hash table
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//
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// Classes: CWidHashTable
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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#include <pch.cxx>
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#pragma hdrstop
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#include "chash.hxx"
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//+---------------------------------------------------------------------------
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//
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// Member: CWidHashTable::CWidHashTable, public
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//
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// Synopsis: Null constructor
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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CWidHashTable::CWidHashTable( BOOL fAggressiveGrowth )
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: _size (0),
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_table(0),
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_count(0),
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_fAggressiveGrowth( fAggressiveGrowth )
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{
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Win4Assert( widInvalid == 0xFFFFFFFF );
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#ifdef DO_STATS
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_cMaxChainLen = 0;
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_cTotalSearches = 0;
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_cTotalLength = 0;
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#endif // DO_STATS
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}
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//+---------------------------------------------------------------------------
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//
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// Member: CWidHashTable::Init, public
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//
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// Synopsis: Initialize hash table
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//
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// Arguments: [count] -- Count of used elements
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// [size] -- Size of [table]
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// [table] -- Hash table
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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void CWidHashTable::Init( ULONG count, ULONG size, WORKID * table )
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{
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_count = count;
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_size = size;
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_table = table;
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} //Init
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//+---------------------------------------------------------------------------
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//
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// Member: CWidHashTable::ReInit, public
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//
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// Synopsis: "ReInitialize" to empty state.
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//
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// Arguments: [count] -- Count of used elements
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// [size] -- Size of [table]
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// [table] -- Hash table
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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void CWidHashTable::ReInit(ULONG count, ULONG size, WORKID* table )
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{
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Init( count, size, table );
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Win4Assert( widInvalid == 0xFFFFFFFF );
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RtlFillMemory( _table, _size * sizeof(_table[0]), 0xFF );
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} //ReInit
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//+---------------------------------------------------------------------------
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//
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// Member: CWidHashTable::GrowSize, public
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//
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// Synopsis: Compute new size for table
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//
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// Arguments: [count] -- Count of to-be-used elements
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//
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// Returns: Suggested new size
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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unsigned CWidHashTable::GrowSize ( unsigned count )
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{
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if ( count < 3 )
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return INIT_HASH_SIZE;
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if ( !_fAggressiveGrowth )
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return count * 2 - 1;
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// Make the hash table as large as possible without eathing too much
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// memory. 4 seems to work ok.
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// The hash table is deemed "full" in IsFull if half of the entries
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// are in use.
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// This is so aggressive in picking a new size because:
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// - rehashing is expensive
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// - walking on hash collisions is expensive
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// - it's resized mostly on the initial scan, and there are probably
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// a lot more files to be added soon.
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unsigned size = count * 4;
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// make it power of two + 1
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// a good approximation of a prime
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for ( unsigned sizeInit = 1; sizeInit < size; sizeInit *= 2 )
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continue;
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return sizeInit - 1;
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} //GrowSize
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//+---------------------------------------------------------------------------
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//
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// Member: CWidHashTable::Add, public
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//
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// Synopsis: Add a new entry
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//
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// Arguments: [hash] -- Best position for entry
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// [wid] -- Workid (entry)
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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void CWidHashTable::Add ( unsigned hash, WORKID wid )
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{
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Win4Assert ( !IsFull() );
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unsigned cur = hash % _size;
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unsigned start = cur;
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unsigned delta = Delta();
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// this loop has to terminate
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// since the table is NOT full!
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while ( _table[cur] != widInvalid && _table[cur] != widUnused )
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{
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cur = (cur + delta) % _size;
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if ( cur == start ) // wrapped around
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{
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Win4Assert( delta != 1 ); // table is full
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delta = 1;
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cur = (cur + 1) % _size;
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}
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}
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_count++;
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_table[cur] = wid;
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} //Add
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//+---------------------------------------------------------------------------
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//
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// Member: CWidHashTable::Remove, public
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//
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// Synopsis: Removes entry from table
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//
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// Arguments: [hash] -- Best position for entry
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// [wid] -- Workid (entry)
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// [fDisableDeletionCheck] -- Should we assert that the deleted
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// entry must be found ?
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//
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// History: 10-Jan-96 KyleP Added header
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//
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// Notes: An entry is 'removed' by marking its slot as unused. An
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// unused slot is like an empty slot, except it does not
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// terminate a CShortWidList.
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//
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//----------------------------------------------------------------------------
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void CWidHashTable::Remove( unsigned hash,
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WORKID wid,
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BOOL fDisableDeletionCheck )
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{
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//
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// This assert not true -- IsFull is checked before adding a new item,
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// so after the add it could be full. If we happen to do a delete at
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// this point, the table could be full and that's ok.
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//
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// Win4Assert ( !IsFull() );
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unsigned cur = hash % _size;
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unsigned start = cur;
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unsigned delta = Delta();
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// this loop has to terminate
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// since the table is NOT full!
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while ( _table[cur] != wid && _table[cur] != widInvalid )
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{
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cur = (cur + delta) % _size;
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if ( cur == start ) // wrapped around
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{
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Win4Assert( delta != 1 ); // table is full
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delta = 1;
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cur = (cur + 1) % _size;
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}
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}
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if ( !fDisableDeletionCheck )
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{
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Win4Assert( wid == _table[cur] );
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}
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if ( _table[cur] == wid )
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{
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_count--;
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_table[cur] = widUnused;
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}
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} //Remove
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//+---------------------------------------------------------------------------
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//
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// Member: CShortWidList::CShortWidList, public
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//
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// Synopsis: Iterator for closed hash 'bucket'.
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//
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// Arguments: [hash] -- Starting position
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// [hashTable] -- Table
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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CShortWidList::CShortWidList ( unsigned hash, CWidHashTable& hashTable )
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: _hashTable(hashTable),
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_counter(0),
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_size( hashTable.Size() )
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{
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if (_size == 0)
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_wid = widInvalid;
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else
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{
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_iCur = hash % _size;
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_iStart = _iCur;
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_delta = hashTable.Delta();
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_wid = _hashTable[_iCur];
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if ( widUnused == _wid )
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_wid = NextWorkId();
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}
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} //CShortWidList
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//+---------------------------------------------------------------------------
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//
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// Member: CShortWidList::NextWorkId, public
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//
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// Returns: Next workid in 'bucket', or widInvalid if at end.
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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WORKID CShortWidList::NextWorkId()
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{
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_wid = widUnused;
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do
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{
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_counter++;
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_iCur = ( _iCur + _delta ) % _size;
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if ( _iCur == _iStart ) // wrapped around
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{
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if (_counter >= _size) // looked at all
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{
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_wid = widInvalid;
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break;
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}
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else
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{
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_delta = 1; // try the fallback delta
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_iCur = (_iCur + 1) % _size;
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_wid = _hashTable[_iCur];
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}
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}
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else
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{
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_wid = _hashTable[_iCur];
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}
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} while ( _wid == widUnused );
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return _wid;
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} //NextWorkId
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//+---------------------------------------------------------------------------
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//
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// Member: CWidHashTable::IsFull, private
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//
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// Returns: TRUE if hash table is full (is running out of slack).
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//
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// History: 10-Jan-96 KyleP Added header
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//
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//----------------------------------------------------------------------------
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BOOL CWidHashTable::IsFull()
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{
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// If the hash table is greater than or equal to half full,
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// it's time to rehash.
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if ( _fAggressiveGrowth )
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return ( _count * 2 ) >= _size;
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return ( _count * 3 / 2 ) >= _size;
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} //IsFull
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