1 /*

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

     3 * All rights reserved.

     4 * This component and the accompanying materials are made available

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

     6 * which accompanies this distribution, and is available

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

     8 *

     9 * Initial Contributors:

    10 * Nokia Corporation - initial contribution.

    11 *

    12 * Contributors:

    13 *

    14 * Description: 

    15 *

    16 */

    17 

    18 

    19 #include <bigint.h>

    20 #include "windowslider.h"

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

    22 

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

    24 	: iExp(aExp), iSize(aWindowSize)

    25 	{

    26 	if(iSize == 0)

    27 		{

    28 		TUint expLen = iExp.BitCount();

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

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

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

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

    33 		//from crypto++

    34 		if( expLen <= 17 )

    35 			iSize = 1;

    36 		else if( expLen <= 24 )

    37 			iSize = 2;

    38 		else if( expLen <= 70 )

    39 			iSize = 3;

    40 		else if( expLen <= 197 )

    41 			iSize = 4;

    42 		else if( expLen <= 539 )

    43 			iSize = 5;

    44 		else if( expLen <= 1434 )

    45 			iSize = 6;

    46 		else 

    47 			iSize = 7;

    48 		}

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

    50 	}

    51 

    52 void TWindowSlider::FindNextWindow(TUint aBegin)

    53 	{

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

    55 	TInt end = aBegin;

    56 	TUint temp = 0;

    57 	iValue = 0;

    58 	TUint j = 0;

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

    60 		{

    61 		TUint saveMask = WORD_BITS - j - 1;

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

    63 		if( temp & (1 << saveMask) )

    64 			{

    65 			end = i;

    66 			iValue |= temp; //last valid substring

    67 			}

    68 		}

    69 

    70 	iLength = aBegin - end + 1;

    71 	iValue >>= (WORD_BITS - iLength);

    72 	}