sl@0: /*
sl@0: * Copyright (c) 2003-2009 Nokia Corporation and/or its subsidiary(-ies).
sl@0: * All rights reserved.
sl@0: * This component and the accompanying materials are made available
sl@0: * under the terms of the License "Eclipse Public License v1.0"
sl@0: * which accompanies this distribution, and is available
sl@0: * at the URL "http://www.eclipse.org/legal/epl-v10.html".
sl@0: *
sl@0: * Initial Contributors:
sl@0: * Nokia Corporation - initial contribution.
sl@0: *
sl@0: * Contributors:
sl@0: *
sl@0: * Description: 
sl@0: *
sl@0: */
sl@0: 
sl@0: 
sl@0: #include <bigint.h>
sl@0: #include "windowslider.h"
sl@0: #include "../common/inlines.h"
sl@0: 
sl@0: TWindowSlider::TWindowSlider(const TInteger& aExp, TUint aWindowSize)
sl@0: 	: iExp(aExp), iSize(aWindowSize)
sl@0: 	{
sl@0: 	if(iSize == 0)
sl@0: 		{
sl@0: 		TUint expLen = iExp.BitCount();
sl@0: 		//These numbers are more or less arbitrary and can be tuned for empirical
sl@0: 		//performance results if desired.  It's a trade off between amount of
sl@0: 		//precomputation (more if larger iSize) and number of iterations
sl@0: 		//(more if smaller iSize).  The current defaults were obtained
sl@0: 		//from crypto++
sl@0: 		if( expLen <= 17 )
sl@0: 			iSize = 1;
sl@0: 		else if( expLen <= 24 )
sl@0: 			iSize = 2;
sl@0: 		else if( expLen <= 70 )
sl@0: 			iSize = 3;
sl@0: 		else if( expLen <= 197 )
sl@0: 			iSize = 4;
sl@0: 		else if( expLen <= 539 )
sl@0: 			iSize = 5;
sl@0: 		else if( expLen <= 1434 )
sl@0: 			iSize = 6;
sl@0: 		else 
sl@0: 			iSize = 7;
sl@0: 		}
sl@0: 	assert(iSize>=1 && iSize<=7);
sl@0: 	}
sl@0: 
sl@0: void TWindowSlider::FindNextWindow(TUint aBegin)
sl@0: 	{
sl@0: 	assert(iExp.Bit(aBegin)); //initial bit must be 1
sl@0: 	TInt end = aBegin;
sl@0: 	TUint temp = 0;
sl@0: 	iValue = 0;
sl@0: 	TUint j = 0;
sl@0: 	for(TInt i=aBegin; i>=0 && j<iSize; i--, j++)
sl@0: 		{
sl@0: 		TUint saveMask = WORD_BITS - j - 1;
sl@0: 		temp |= iExp.Bit(i) << saveMask;
sl@0: 		if( temp & (1 << saveMask) )
sl@0: 			{
sl@0: 			end = i;
sl@0: 			iValue |= temp; //last valid substring
sl@0: 			}
sl@0: 		}
sl@0: 
sl@0: 	iLength = aBegin - end + 1;
sl@0: 	iValue >>= (WORD_BITS - iLength);
sl@0: 	}
sl@0: