--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/crypto/weakcrypto/source/bigint/windowslider.cpp Fri Jun 11 15:32:35 2010 +0300
@@ -0,0 +1,73 @@
+/*
+* 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);
+ }
+