Concatenate Boost::Dynamic_Bitset - Performance

#include <iostream>
#include <boost/dynamic_bitset.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
using namespace boost::posix_time;


const int CYCLES = 10000;


boost::dynamic_bitset<> concatenateBitsets(const boost::dynamic_bitset<>& first, const boost::dynamic_bitset<>& second)
{
    boost::dynamic_bitset<> firstCopy(first);
    boost::dynamic_bitset<> secondCopy(second);

    //Increase the size of the bit buffer to fit the data being placed in it
    firstCopy.resize(first.size() + second.size());
    secondCopy.resize(first.size() + second.size());

    //shift the bits in the firstCopy to the left
    firstCopy <<= second.size();

    //"copy" the bits from the secondCopy into the firstCopy
    firstCopy |= secondCopy;
    return firstCopy;
}


int main()
{
    //init the time-counting objects
    ptime firstValue = ptime(microsec_clock::local_time());
    ptime secondValue = ptime(microsec_clock::local_time());
    time_duration diff = secondValue - firstValue;

    //init the bitsets
    boost::dynamic_bitset<> intBitset(32, 0xffffaaaa);
    boost::dynamic_bitset<> boolBitset(1, true);
    boost::dynamic_bitset<> charBitset(8, 'x');



    //Test the String-Append method
    firstValue = ptime(microsec_clock::local_time());

    std::ostringstream bitsetConcat;
    bitsetConcat << intBitset; //initial fill
    for(int index = 0; index < CYCLES; index++)
    {
        bitsetConcat << intBitset;
        bitsetConcat << boolBitset;
        bitsetConcat << charBitset;
    }
    boost::dynamic_bitset<> bitsetConcatenated( bitsetConcat.str() );

    secondValue = ptime(microsec_clock::local_time());
    diff = secondValue - firstValue;
    std::cout << "Stringmethod lasts " << diff.fractional_seconds() << " msec" << std::endl;



    //Test the Bitshift method
    firstValue = ptime(microsec_clock::local_time());

    boost::dynamic_bitset<> bitsetConcat2(intBitset); //initial fill
    for(int index = 0; index < CYCLES; index++)
    {
        bitsetConcat2 = concatenateBitsets(bitsetConcat2, intBitset);
        bitsetConcat2 = concatenateBitsets(bitsetConcat2, boolBitset);
        bitsetConcat2 = concatenateBitsets(bitsetConcat2, charBitset);
    }
    secondValue = ptime(microsec_clock::local_time());
    diff = secondValue - firstValue;
    std::cout << "Shiftmethod lasts " << diff.fractional_seconds() << " msec" << std::endl;

    return 0;
}