/*

 * Copyright (c) 2003-2009 Nokia Corporation and/or its subsidiary(-ies).

 * All rights reserved.

 * This component and the accompanying materials are made available

 * under the terms of the License "Eclipse Public License v1.0"

 * which accompanies this distribution, and is available

 * at the URL "http://www.eclipse.org/legal/epl-v10.html".

 *

 * Initial Contributors:

 * Nokia Corporation - initial contribution.

 *

 * Contributors:

 *

 * Description: 

 *

 */

 #include <bigint.h>

 #include "windowslider.h"

 #include "../common/inlines.h"

 TWindowSlider::TWindowSlider(const TInteger& aExp, TUint aWindowSize)

 	: iExp(aExp), iSize(aWindowSize)

 	{

 	if(iSize == 0)

 		{

 		TUint expLen = iExp.BitCount();

 		//These numbers are more or less arbitrary and can be tuned for empirical

 		//performance results if desired.  It's a trade off between amount of

 		//precomputation (more if larger iSize) and number of iterations

 		//(more if smaller iSize).  The current defaults were obtained

 		//from crypto++

 		if( expLen <= 17 )

 			iSize = 1;

 		else if( expLen <= 24 )

 			iSize = 2;

 		else if( expLen <= 70 )

 			iSize = 3;

 		else if( expLen <= 197 )

 			iSize = 4;

 		else if( expLen <= 539 )

 			iSize = 5;

 		else if( expLen <= 1434 )

 			iSize = 6;

 		else 

 			iSize = 7;

 		}

 	assert(iSize>=1 && iSize<=7);

 	}

 void TWindowSlider::FindNextWindow(TUint aBegin)

 	{

 	assert(iExp.Bit(aBegin)); //initial bit must be 1

 	TInt end = aBegin;

 	TUint temp = 0;

 	iValue = 0;

 	TUint j = 0;

 	for(TInt i=aBegin; i>=0 && j<iSize; i--, j++)

 		{

 		TUint saveMask = WORD_BITS - j - 1;

 		temp |= iExp.Bit(i) << saveMask;

 		if( temp & (1 << saveMask) )

 			{

 			end = i;

 			iValue |= temp; //last valid substring

 			}

 		}

 	iLength = aBegin - end + 1;

 	iValue >>= (WORD_BITS - iLength);

 	}