// Copyright (c) 1995-2009 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:

//

//  Collection of common constants, utility functions, etc. for the file server and file systems.

//  Definitions here must be filesystem-agnostic, i.e. generic enougs to be used by every file system

//

//  This is the internal file and must not be exported.

/**

    @file

    @internalTechnology

*/

#include "bit_vector.h"

//#######################################################################################################################################

//#   RBitVector class implementation

//#######################################################################################################################################

const TUint32 K_FFFF = 0xFFFFFFFF; //-- all one bits, beware rigth shifts of signed integers!

RBitVector::RBitVector()

          :iNumBits(0), ipData(NULL), iNumWords(0)

    {

    }

RBitVector::~RBitVector()

    {

    Close();

    }

/**

    Panics.

    @param aPanicCode   a panic code

*/

void RBitVector::Panic(TPanicCode aPanicCode) const

    {

    _LIT(KPanicCat,"RBitVector");

    User::Panic(KPanicCat, aPanicCode);

    }

/** explicitly closes the object and deallocates memory */

void RBitVector::Close()

    {

    iNumBits = 0;

    iNumWords =0;

    User::Free(ipData);

    ipData = NULL;

    }

//-----------------------------------------------------------------------------

/**

    Comparison perator.

    @param  aRhs a vector to compate with.

    @panic ESizeMismatch in the case of different vector sizes

*/

TBool RBitVector::operator==(const RBitVector& aRhs) const

    {

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    __ASSERT_ALWAYS(iNumBits == aRhs.iNumBits, Panic(ESizeMismatch));

    if(!iNumBits)

        return ETrue; //-- comparing 0-lenght arrays

    if(this == &aRhs)

        {//-- comparing with itself, potential source of errors

        ASSERT(0);

        return ETrue; 

        }

    if(iNumWords >= 1)

        {

        const TUint32 cntBytes = (iNumBits >> 5) << 2; //-- bytes to compare

        if(memcompare((const TUint8*)ipData, cntBytes, (const TUint8*)aRhs.ipData, cntBytes))

            return EFalse;

        }

    const TUint32 bitsRest  = iNumBits & 0x1F;

    if(bitsRest)

        {

        const TUint32 mask = K_FFFF >> (32-bitsRest);

        return ( (ipData[iNumWords-1] & mask) == (aRhs.ipData[iNumWords-1] & mask) );

        }

    return ETrue;

    }

TBool RBitVector::operator!=(const RBitVector& aRhs) const  

    {

    return ! ((*this) == aRhs);

    } 

//-----------------------------------------------------------------------------

/** The same as Create(), but leaves on error */

void RBitVector::CreateL(TUint32 aNumBits)

    {

    User::LeaveIfError(Create(aNumBits));

    }

/**

    Create the vector with the size of aNumBits bits.

    @return system-wide error codes:

        KErrNoMemory    unable to allocate sufficient amount of memory for the array

        KErrInUse       an attempt to call Create() for non-empty vector. Close it first.

        KErrArgument    invalid aNumBits value == 0

*/

TInt RBitVector::Create(TUint32 aNumBits)

    {

    if(ipData)

        return KErrInUse; //-- array is already in use. Close it first.

    if(!aNumBits)

        return KErrArgument;

    //-- memory is allocated by word (32 bit) quiantities

    const TUint32 numWords = (aNumBits >> 5) + ((aNumBits & 0x1F) > 0 ? 1:0);

    ipData = (TUint32*)User::AllocZ(numWords << 2);

    if(!ipData)

        return KErrNoMemory;

    iNumBits  = aNumBits;

    iNumWords = numWords;

    return KErrNone;

    }

/**

    Fill a bit vector with a given bit value

    @param aVal a bit value

*/

void RBitVector::Fill(TBool aVal)

    {

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    memset(ipData, (aVal ? 0xFF : 0x00), iNumWords << 2);

    }

/** Invert all bits in a bit vector */

void RBitVector::Invert()

{

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    for(TUint32 i=0; i<iNumWords; ++i)

        ipData[i] ^= K_FFFF;

}

/**

    Perform "And" operation between 2 vectors. They shall be the same size.

    @param  aRhs a vector from the right hand side

    @panic ESizeMismatch in the case of different vector sizes

*/

void RBitVector::And(const RBitVector& aRhs)

    {

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    __ASSERT_ALWAYS(iNumBits == aRhs.iNumBits, Panic(ESizeMismatch));

    for(TUint32 i=0; i<iNumWords; ++i)

        {

        ipData[i] &= aRhs.ipData[i];

        }

    }

/**

    Perform "Or" operation between 2 vectors. They shall be the same size.    

    @param  aRhs a vector from the right hand side

    @panic ESizeMismatch in the case of different vector sizes

*/

void RBitVector::Or(const RBitVector& aRhs)

    {

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    __ASSERT_ALWAYS(iNumBits == aRhs.iNumBits, Panic(ESizeMismatch));

    for(TUint32 i=0; i<iNumWords; ++i)

        {

        ipData[i] |= aRhs.ipData[i];

        }

    }

/**

    Perform "Xor" operation between 2 vectors. They shall be the same size.    

    @param  aRhs a vector from the right hand side

    @panic ESizeMismatch in the case of different vector sizes

*/

void RBitVector::Xor(const RBitVector& aRhs)

    {

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    __ASSERT_ALWAYS(iNumBits == aRhs.iNumBits, Panic(ESizeMismatch));

    for(TUint32 i=0; i<iNumWords; ++i)

        {

        ipData[i] ^= aRhs.ipData[i];

        }

    }

//-----------------------------------------------------------------------------

/**

    Fill a range from bit number "aIndexFrom" to "aIndexTo" inclusively with the value of aVal

    @param  aIndexFrom  start bit number (inclusive)

    @param  aIndexTo    end bit number (inclusive)

    @param  aVal        the value to be used to fill the range (0s or 1s)

*/

void RBitVector::Fill(TUint32 aIndexFrom, TUint32 aIndexTo, TBool aVal)

    {

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    //-- swap indexes if they are not in order

    if(aIndexFrom > aIndexTo)

        {

        const TUint32 tmp = aIndexFrom;

        aIndexFrom = aIndexTo;

        aIndexTo = tmp;

        }

    __ASSERT_ALWAYS((aIndexFrom < iNumBits) && (aIndexTo < iNumBits), Panic(EIndexOutOfRange));

    const TUint32 wordStart = WordNum(aIndexFrom);

    const TUint32 wordTo    = WordNum(aIndexTo);

    if(aVal)

        {//-- filling a range with '1'

        TUint32 shift = BitInWord(aIndexFrom);

        const TUint32 mask1 = (K_FFFF >> shift) << shift;

        TUint32 mask2 = K_FFFF;

        shift = 1+BitInWord(aIndexTo);

        if(shift < 32)

            {

            mask2 = ~((mask2 >> shift) << shift);

            }

        if(wordTo == wordStart)

            {//-- a special case, filling is in the same word

            ipData[wordStart] |= (mask1 & mask2);

            }

        else

            {

            ipData[wordStart] |= mask1; 

            ipData[wordTo]    |= mask2;

            const TUint32 wholeWordsBetween = wordTo - wordStart - 1; //-- whole words that can be bulk filled

            if(wholeWordsBetween)

                memset(ipData+wordStart+1, 0xFF, wholeWordsBetween << 2);

            }

        }

    else

        {//-- filling a range with '0'

        TUint32 shift = BitInWord(aIndexFrom);

        const TUint32 mask1 = ~((K_FFFF >> shift) << shift);

        TUint32 mask2 = 0;

        shift = 1+BitInWord(aIndexTo);

        if(shift < 32)

            {

            mask2 = ((K_FFFF >> shift) << shift);

            }

        if(wordTo == wordStart)

            {//-- a special case, filling is in the same word

            ipData[wordStart] &= (mask1 | mask2);

            }

        else

            {

            ipData[wordStart] &= mask1; 

            ipData[wordTo]    &= mask2;

            const TUint32 wholeWordsBetween = wordTo - wordStart - 1; //-- whole words that can be bulk filled

            if(wholeWordsBetween)

                memset(ipData+wordStart+1, 0x00, wholeWordsBetween << 2);

            }

        }

    }

//-----------------------------------------------------------------------------

/**

    Search for a specified bit value ('0' or '1') in the vector from the given position.

    @param  aStartPos   zero-based index; from this position the search will start. This position isn't included to the search.

                        On return may contain a new position if the specified bit is found in specified direction.

    @param  aBitVal     zero or non-zero bit to search.

    @param  aDir        Specifies the search direction

    @return ETrue if the specified bit value is found; aStartPos gets updated.

            EFalse otherwise.

*/

TBool RBitVector::Find(TUint32& aStartPos, TBool aBitVal, TFindDirection aDir) const

    {

    __ASSERT_ALWAYS(aStartPos < iNumBits, Panic(EIndexOutOfRange));

    ASSERT(iNumWords && ipData);

    switch(aDir)

        {

        case ERight:    //-- Search from the given position to the right

            return FindToRight(aStartPos, aBitVal);

        case ELeft:     //-- Search from the given position to the left (towards lower index)

            return FindToLeft(aStartPos, aBitVal);

        case ENearestL: //-- Search for the nearest value in both directions starting from left

            return FindNearest(aStartPos, aBitVal, ETrue);

        case ENearestR: //-- Search for the nearest value in both directions starting from right

            return FindNearest(aStartPos, aBitVal, EFalse);

        default:

            Panic(EWrondFindDirection);

            return EFalse;

        };

    }

//-----------------------------------------------------------------------------

/**

    Internal method to look for a given bit value in the right direction.

    see TBool RBitVector::Find(...)

*/

TBool RBitVector::FindToRight(TUint32& aStartPos, TBool aBitVal) const

    {

    if(aStartPos >= iNumBits-1)

        return EFalse; //-- no way to the right

    const TUint32 startPos = aStartPos+1;

    const TUint32 fInvert = aBitVal ? 0 : K_FFFF; //-- invert everything if we are looking for '0' bit

    TUint32 wordNum = WordNum(startPos);

    TUint32 val = ipData[wordNum] ^ fInvert;

    if(wordNum == iNumWords-1)

        {//-- process the last word in the array, some higher bits might not belong to the bit vector

        val = MaskLastWord(val);

        }

    const TUint32 shift = BitInWord(startPos);

    val = (val >> shift) << shift; //-- mask unused low bits

    if(val)

        {//-- there are '1' bits in the current word

        goto found;

        }

    else

        {//-- search in higher words

        wordNum++;

        while(iNumWords-wordNum > 1)

            {

            val = ipData[wordNum] ^ fInvert;

            if(val)

                goto found;

            wordNum++;

            }

        if(wordNum == iNumWords-1)

            {//-- process the last word in the array, some higher bith might not belong to the bit vector

            val = ipData[wordNum] ^ fInvert;

            val = MaskLastWord(val);

            if(val)

                goto found;

            }

        }

    return EFalse; //-- haven't found anything

  found:

    val &= (~val+1); //-- select rightmost bit

    aStartPos = (wordNum << 5)+Log2(val);

    return ETrue;

    }

//-----------------------------------------------------------------------------

/**

    Internal method to look for a given bit value in the left direction.

    see TBool RBitVector::Find(...)

*/

TBool RBitVector::FindToLeft(TUint32& aStartPos, TBool aBitVal) const

{

    if(!aStartPos)

        return EFalse; //-- no way to the left

    const TUint32 startPos=aStartPos-1;

    const TUint32 fInvert = aBitVal ? 0 : K_FFFF; //-- invert everything if we are looking for '0' bit

    TUint32 wordNum = WordNum(startPos);

    TUint32 val = ipData[wordNum] ^ fInvert;

    const TUint32 shift = 31-(BitInWord(startPos));

    val = (val << shift) >> shift; //-- mask unused high bits

    if(val)

    {//-- there are '1' bits in the current word

        goto found;

    }

    else

    {//-- search in the lower words

        while(wordNum)

        {

            wordNum--;

            val=ipData[wordNum] ^ fInvert;

            if(val)

                goto found;

        }

    }

    return EFalse; //-- nothing found

 found:

    aStartPos = (wordNum << 5)+Log2(val);

    return ETrue;

}

//-----------------------------------------------------------------------------

/**

    Internal method to look for a given bit value in the both directions.

    see TBool RBitVector::Find(...)

*/

TBool RBitVector::FindNearest(TUint32& aStartPos, TBool aBitVal, TBool aToLeft) const

{

    if(iNumBits < 2)

        return EFalse;

    if(aStartPos == 0)

        return FindToRight(aStartPos, aBitVal);

    if(aStartPos == iNumBits-1)

        return FindToLeft(aStartPos, aBitVal);

    const TUint32 fInvert = aBitVal ? 0 : K_FFFF; //-- invert everything if we are looking for '0' bit

    TUint32 wordNum = WordNum(aStartPos);

    TUint32 l_Idx; //-- index of the word to the left

    TUint32 r_Idx; //-- index of the word to the right

    l_Idx = r_Idx = wordNum;

    TBool   noWayLeft  = (wordNum == 0);            //-- if we are in the first word

    TBool   noWayRight = (wordNum == iNumWords-1);  //-- if we are in the last word

    //-- look in the current word first

    TUint32 val = ipData[wordNum] ^ fInvert;

    if(noWayRight)

    {   //-- this is the last word in the array, mask unused high bits in the last word

        val = MaskLastWord(val);

    }

    const TUint32 bitPos = aStartPos & 0x1F;

    val &= ~(1<<bitPos); //-- mask the bit at current position

    if(val == 0)

    {//-- no '1' bits in the current word

        noWayLeft  = ItrLeft(l_Idx);

        noWayRight = ItrRight(r_Idx);

    }

    else if(bitPos == 0)

    {

        noWayLeft = ItrLeft(l_Idx); //-- move to the previous word

    }

    else if(bitPos == 31)

    {

        noWayRight = ItrRight(r_Idx); //-- move to the next word

    }

    else

    {//-- look in the current word, in both halves to the left and right from the start position

        const TUint32 shift1 = 32-bitPos;

        const TUint32 partLo = (val << shift1) >> shift1; //-- towards lower bits

        const TUint32 shift2 = bitPos+1;

        const TUint32 partHi = (val >> shift2) << shift2; //-- towards higher bits 

        if(partLo && !partHi) //-- only lower part has '1' bits   

        {

            aStartPos = (wordNum << 5)+Log2(partLo);

            return ETrue;

        }

        else if(!partLo && partHi) //-- only higher part has '1' bits

        {

            aStartPos = (wordNum << 5)+Log2( (partHi & (~partHi+1)) );

            return ETrue;

        }

        else if(partLo && partHi) //-- both parts contain '1' bits, select the nearest one

        {

            const TUint32 posL = (wordNum << 5)+Log2(partLo);

            const TUint32 posR = (wordNum << 5)+Log2( (partHi & (~partHi+1)) );

            ASSERT(aStartPos > posL);

            ASSERT(posR > aStartPos);

            const TUint32 distL = aStartPos-posL;

            const TUint32 distR = posR-aStartPos;

            if(distL < distR)

            {

                aStartPos = posL;

                return ETrue;

            }

            else if(distL > distR)

            {

                aStartPos = posR;

                return ETrue;

            }

            else

            {//-- distL == distR, take into account search priority

                aStartPos = aToLeft ? posL : posR;

                return ETrue;

            }

        }

        else //-- (!partLo && !partHi), nothing in the current word

        {

            ASSERT(0);

        }

    }// if(bitPos > 0 && bitPos < 31)

    //-- now we are processing separate words from both sides of the search position

    for(;;)

    { 

        TUint32 wL = ipData[l_Idx] ^ fInvert;

        TUint32 wR = ipData[r_Idx] ^ fInvert;

        if(r_Idx == iNumWords-1)

        {   //-- this is the last word in the array, mask unused high bits in the last word

            wR = MaskLastWord(wR);

        }

        if(wL && !wR)

        {

            aStartPos = (l_Idx << 5)+Log2(wL);

            return ETrue;

        }

        else if(!wL && wR)

        {

            aStartPos = (r_Idx << 5)+Log2( (wR & (~wR+1)) );

            return ETrue;

        }

        else if(wL && wR)

        {

            const TUint32 posL = (l_Idx << 5)+Log2(wL);

            const TUint32 posR = (r_Idx << 5)+Log2( (wR & (~wR+1)) );

            ASSERT(aStartPos > posL);

            ASSERT(posR > aStartPos);

            const TUint32 distL = aStartPos-posL;

            const TUint32 distR = posR-aStartPos;

            if(distL < distR)

            {

                aStartPos = posL;

                return ETrue;

            }

            else if(distL > distR)

            {

                aStartPos = posR;

                return ETrue;

            }

            else

            {//-- distL == distR, take into account search priority

                aStartPos = aToLeft ? posL : posR;

                return ETrue;

            }

        }//else if(wL && wR)

        if(noWayLeft)

        {

            aStartPos = r_Idx << 5;

            return FindToRight(aStartPos, aBitVal);

        }

        else

        {

            noWayLeft  = ItrLeft(l_Idx);

        }

        if(noWayRight)

        {

            aStartPos = l_Idx << 5;

            return FindToLeft(aStartPos, aBitVal);

        }

        else

        {    

            noWayRight = ItrRight(r_Idx);

        }

   }//for(;;)

    //return EFalse;

}

//-----------------------------------------------------------------------------

/**

    Find out if two vectors are different.

    @param  aRhs        vector to compare with

    @param  aDiffIndex  if there is a differene, here will be the number of the first different bit

    @return ETrue if vectors differ, EFalse, if they are identical.

*/

TBool RBitVector::Diff(const RBitVector& aRhs, TUint32& aDiffIndex) const

{

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    __ASSERT_ALWAYS(iNumBits == aRhs.iNumBits, Panic(ESizeMismatch));

    ASSERT(iNumWords > 0);

    TUint32 diffWord=0;

    TUint32 wordNum=0;

    //-- compare all but the last word in the array

    for(wordNum=0; wordNum < iNumWords-1; ++wordNum)

    {

        diffWord = ipData[wordNum] ^ aRhs.ipData[wordNum];

        if(diffWord)

            break;  //-- found difference

    }

    //-- process the last word in the array

    if(!diffWord)

    {

        diffWord = MaskLastWord(ipData[wordNum]) ^ MaskLastWord(aRhs.ipData[wordNum]);

    }

    if(!diffWord)

        return EFalse; //-- vectors are the same

    //-- calculate the position of the bit that different.

    diffWord &= (~diffWord+1); //-- select rightmost bit

    aDiffIndex = (wordNum << 5)+Log2(diffWord);

    return ETrue;

}

//-----------------------------------------------------------------------------

/**

    Iterate to the left (towards lower index) in the array of words ipData

    @param  aIdx index within ipData array to be decremented; if it's possible to move left, it will be decreased

    @return ETrue if there is no way left i.e. aIdx is 0. EFalse otherwise and aIdx decreased.

*/

TBool RBitVector::ItrLeft(TUint32& aIdx) const

{

    if(aIdx == 0)

        return ETrue;

    else

    {

        aIdx--;

        return EFalse;

    }

}

//-----------------------------------------------------------------------------

/**

    Iterate to the right (towards higher index) in the array of words ipData

    @param  aIdx index within ipData array to be incremented; if it's possible to move right, it will be increased

    @return ETrue if there is no way right i.e. aIdx corresponds to the last word. EFalse otherwise and aIdx increased.

*/

TBool RBitVector::ItrRight(TUint32& aIdx) const

{

    if(aIdx < iNumWords-1)

    {

        aIdx++;

        return EFalse;

    }

    else

        return ETrue;

}

//-----------------------------------------------------------------------------

/**

    Import data to the internal bit vector representation.

    Just replaces number of bytes from apData to the ipData.

    @param aStartBit starting bit number. Must have 8-bit alignment.

    @param aNumBits  number of bits to import; granularity: 1 bit, i.e. it can be 177, for example.

    @param apData    pointer to the data (bitstream) to import.

*/

void RBitVector::DoImportData(TUint32 aStartBit, TUint32 aNumBits, const TAny* apData)

{

    ASSERT(aNumBits);

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    //-- check parameters granularity. aStartBit must have 8-bit alignment

    __ASSERT_ALWAYS(!(aStartBit & 0x07), Panic(EDataAlignment));

    __ASSERT_ALWAYS(iNumWords && (aStartBit+aNumBits <= iNumBits), Panic(EIndexOutOfRange));

    const TUint     bitsTail = aNumBits & 0x07;

    const TUint32   nBytes = aNumBits >> 3;

    if(nBytes)

    {//-- copy full array of bytes

        const TUint32   startByte = aStartBit >> 3;

        Mem::Copy(((TUint8*)ipData) + startByte, apData, nBytes);

    }

    if(bitsTail)

    {//-- we need to copy trailing bits from the input data to the corresponding byte of the internal array

        const TUint8 mask   = (TUint8)(0xFF >> (8-bitsTail));

        const TUint8 orMask = (TUint8)( *((const TUint8*)apData + nBytes) & mask);

        const TUint8 andMask= (TUint8)~mask;

        TUint8* pbData = (TUint8*)ipData + nBytes;

        *pbData &= andMask;

        *pbData |= orMask;

    }

}

//-----------------------------------------------------------------------------

/**

    Export data from the internal bit vector buffer to the external one.

    @param aStartBit starting bit number. Must have 8-bit alignment.

    @param aNumBits  number of bits to export, must comprise the whole byte, i.e. be multiple of 8.

                     The client is responsible for masking extra bits it doesn't need. 

                     Another implication: e.g. if the bitvector consists of 3 bits, this value must be 8.

                     The value of bits 3-7 in the aData[0] will be undefined.

    @param aData     destination data descriptor   

*/

void  RBitVector::DoExportData(TUint32 aStartBit, TUint32 aNumBits, TDes8& aData) const

{

    ASSERT(aNumBits);

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    //-- check parameters granularity.

    __ASSERT_ALWAYS(!(aStartBit & 0x07), Panic(EDataAlignment)); //-- aStartBit must have 8-bit alignment

    __ASSERT_ALWAYS(!(aNumBits & 0x07), Panic(EDataAlignment));  //-- number of bits shall comprise a byte

    __ASSERT_ALWAYS(iNumWords && (aStartBit+aNumBits <= (iNumWords << (KBitsInByteLog2+sizeof(TUint32))) ), Panic(EIndexOutOfRange));

    const TUint32 nBytes = aNumBits >> 3;

    const TUint32 startByte = aStartBit >> 3;

    aData.SetLength(nBytes);

    aData.Copy(((const TUint8*)ipData) + startByte, nBytes);

}

//-----------------------------------------------------------------------------

/**

    @return number of bits set to '1' in the vector

*/

TUint32 RBitVector::Num1Bits() const

{

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    if(!iNumBits)

        return 0;

    TUint32 cntBits = 0;

    TUint32 wordNum;

    for(wordNum=0; wordNum < iNumWords-1; ++wordNum)

    {

        cntBits += Count1Bits(ipData[wordNum]);

    }

    //-- process the last word, it shall be masked

    cntBits += Count1Bits(MaskLastWord(ipData[wordNum]));

    return cntBits;

}

//-----------------------------------------------------------------------------

/**

    @return number of bits set to '0' in the vector

*/

TUint32 RBitVector::Num0Bits() const

{

    return iNumBits - Num1Bits();

}

//-----------------------------------------------------------------------------

/**

    Calculate number of '1' bits in the range from aIndexFrom to aIndexTo inclusively

    @param  aIndexFrom  starting index; bit[aIndexFrom] is included to the search

    @param  aIndexTo    ending index;   bit[aIndexTo] is included to the search

    @return number of bits set to '1' in the slice

*/

TUint32 RBitVector::Num1Bits(TUint32 aIndexFrom, TUint32 aIndexTo) const

{

    __ASSERT_ALWAYS(ipData, Panic(ENotInitialised));

    __ASSERT_ALWAYS(aIndexTo < iNumBits && aIndexFrom <= aIndexTo, Panic(EIndexOutOfRange));

    const TUint32 wordFrom = WordNum(aIndexFrom); //?const

    const TUint32 wordTo   = WordNum(aIndexTo);

    if(wordFrom == wordTo)

    {//-- the same word

        TUint32 word = ipData[wordFrom];

        const TUint32 shMaskR = BitInWord(aIndexFrom);

        word >>= shMaskR; word <<= shMaskR; //-- zero low bits

        const TUint32 shMaskL = 31-BitInWord(aIndexTo);

        word <<= shMaskL;  //-- zero high bits

        return Count1Bits(word);

    } 

    TUint32 bitsCnt = 0;

    TUint32 wordsBetween = wordTo - wordFrom - 1;

    //-- count '1' bits in the termial words

    TUint32 word = ipData[wordFrom];

    const TUint32 shMaskR = BitInWord(aIndexFrom);

    word >>= shMaskR; //-- zero low bits

    bitsCnt += Count1Bits(word);

    word = ipData[wordTo];

    const TUint32 shMaskL = 31-BitInWord(aIndexTo);

    word <<= shMaskL;  //-- zero high bits

    bitsCnt += Count1Bits(word);

    //-- count '1' bits in the words between terminal ones

    TUint32 wordIdx = wordFrom+1;

    while(wordsBetween--)

    {

        bitsCnt += Count1Bits(ipData[wordIdx]);

    }

    return bitsCnt;

}