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 * TWindowSlider class implementation

    16 *

    17 */

    18 

    19 

    20 /**

    21  @file 

    22  @internalComponent

    23 */

    24  

    25 #ifndef __WINDOWSLIDER_H__

    26 #define __WINDOWSLIDER_H__

    27 

    28 #include <e32std.h>

    29 

    30 class TInteger; 

    31 /** Utility class used by our fast exponentiation routines.\n\n

    32  * See HAC 14.85 for an explanation of how window sliding helps speed things up.

    33  * @internalComponent

    34  */

    35 class TWindowSlider

    36 {

    37 public:

    38 	/** 

    39 	 * @param aExp The exponent you are using.

    40 	 * @param aWindowSize The window size.  Leave as default value for the

    41 	 * constructor to pick a window size appropriate for the given aExp

    42 	 * @internalComponent

    43 	 */

    44 	TWindowSlider(const TInteger& aExp, TUint aWindowSize=0);

    45 	/**

    46 	 * Finds the next "window" as defined by HAC 14.85.  The actual bitstring

    47 	 * value is in iValue and it's length in iLength.  These remain valid until

    48 	 * the next call to FindNextWindow()

    49 	 */

    50 	void FindNextWindow(TUint aBegin);

    51 	inline TUint WindowSize(void) {return iSize;}

    52 	inline TUint Value(void) {return iValue;}

    53 	inline TUint Length(void) {return iLength;}

    54 

    55 private:

    56 	const TInteger& iExp; ///the exponent all this is being calculated on

    57 	TUint iSize;  ///The size of the sliding window

    58 	TUint iValue; ///the value found by the most recent FindNextWindow() call

    59 	TUint iLength;///the bit length of the iValue

    60 };

    61 

    62 #endif