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1 /* |
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2 * Copyright (c) 2003-2009 Nokia Corporation and/or its subsidiary(-ies). |
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3 * All rights reserved. |
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4 * This component and the accompanying materials are made available |
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5 * under the terms of the License "Eclipse Public License v1.0" |
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6 * which accompanies this distribution, and is available |
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7 * at the URL "http://www.eclipse.org/legal/epl-v10.html". |
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8 * |
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9 * Initial Contributors: |
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10 * Nokia Corporation - initial contribution. |
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11 * |
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12 * Contributors: |
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13 * |
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14 * Description: |
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15 * |
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16 */ |
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17 |
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18 |
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19 #include <bigint.h> |
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20 #include "windowslider.h" |
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21 #include "../common/inlines.h" |
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22 |
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23 TWindowSlider::TWindowSlider(const TInteger& aExp, TUint aWindowSize) |
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24 : iExp(aExp), iSize(aWindowSize) |
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25 { |
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26 if(iSize == 0) |
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27 { |
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28 TUint expLen = iExp.BitCount(); |
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29 //These numbers are more or less arbitrary and can be tuned for empirical |
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30 //performance results if desired. It's a trade off between amount of |
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31 //precomputation (more if larger iSize) and number of iterations |
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32 //(more if smaller iSize). The current defaults were obtained |
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33 //from crypto++ |
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34 if( expLen <= 17 ) |
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35 iSize = 1; |
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36 else if( expLen <= 24 ) |
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37 iSize = 2; |
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38 else if( expLen <= 70 ) |
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39 iSize = 3; |
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40 else if( expLen <= 197 ) |
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41 iSize = 4; |
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42 else if( expLen <= 539 ) |
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43 iSize = 5; |
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44 else if( expLen <= 1434 ) |
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45 iSize = 6; |
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46 else |
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47 iSize = 7; |
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48 } |
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49 assert(iSize>=1 && iSize<=7); |
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50 } |
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51 |
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52 void TWindowSlider::FindNextWindow(TUint aBegin) |
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53 { |
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54 assert(iExp.Bit(aBegin)); //initial bit must be 1 |
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55 TInt end = aBegin; |
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56 TUint temp = 0; |
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57 iValue = 0; |
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58 TUint j = 0; |
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59 for(TInt i=aBegin; i>=0 && j<iSize; i--, j++) |
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60 { |
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61 TUint saveMask = WORD_BITS - j - 1; |
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62 temp |= iExp.Bit(i) << saveMask; |
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63 if( temp & (1 << saveMask) ) |
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64 { |
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65 end = i; |
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66 iValue |= temp; //last valid substring |
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67 } |
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68 } |
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69 |
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70 iLength = aBegin - end + 1; |
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71 iValue >>= (WORD_BITS - iLength); |
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72 } |
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73 |