qt-everywhere-src-5.15.1/qtbase/src/corelib/tools/qalgorithms.qdoc

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/*!
    \headerfile <QtAlgorithms>
    \title Generic Algorithms
    \ingroup funclists
    \keyword generic algorithms

    \brief The <QtAlgorithms> header includes the generic, template-based algorithms.

    Qt provides a number of global template functions in \c
    <QtAlgorithms> that work on containers and perform small tasks to
    make life easier, such as qDeleteAll(), which invokes \c{operator delete}
    on all items in a given container or in a given range.
    You can use these algorithms with any \l {container
    class} that provides STL-style iterators, including Qt's QList,
    QLinkedList, QVector, QMap, and QHash classes.

    Most algorithms take \l {STL-style iterators} as parameters. The
    algorithms are generic in the sense that they aren't bound to a
    specific iterator class; you can use them with any iterators that
    meet a certain set of requirements.

    Different algorithms can have different requirements for the
    iterators they accept. For example, qFill() accepts two
    \l {forward iterators}. The iterator types required are specified
    for each algorithm. If an iterator of the wrong type is passed (for
    example, if QList::ConstIterator is passed as an
    \l {Output Iterators}{output iterator}), you will always get a
    compiler error, although not necessarily a very informative one.

    Some algorithms have special requirements on the value type
    stored in the containers. For example,
    qDeleteAll() requires that the value type is a
    non-const pointer type (for example, QWidget *). The value type
    requirements are specified for each algorithm, and the compiler
    will produce an error if a requirement isn't met.

    The generic algorithms can be used on other container classes
    than those provided by Qt and STL. The syntax of STL-style
    iterators is modeled after C++ pointers, so it's possible to use
    plain arrays as containers and plain pointers as iterators. A
    common idiom is to use qBinaryFind() together with two static
    arrays: one that contains a list of keys, and another that
    contains a list of associated values. For example, the following
    code will look up an HTML entity (e.g., \c &amp;) in the \c
    name_table array and return the corresponding Unicode value from
    the \c value_table if the entity is recognized:

    \snippet code/doc_src_qalgorithms.cpp 2

    This kind of code is for advanced users only; for most
    applications, a QMap- or QHash-based approach would work just as
    well:

    \snippet code/doc_src_qalgorithms.cpp 3

    \section1 Types of Iterators

    The algorithms have certain requirements on the iterator types
    they accept, and these are specified individually for each
    function. The compiler will produce an error if a requirement
    isn't met.

    \section2 Input Iterators

    An \e{input iterator} is an iterator that can be used for reading
    data sequentially from a container. It must provide the following
    operators: \c{==} and \c{!=} for comparing two iterators, unary
    \c{*} for retrieving the value stored in the item, and prefix
    \c{++} for advancing to the next item.

    The Qt containers' iterator types (const and non-const) are all
    input iterators.

    \section2 Output Iterators

    An output iterator is an iterator that can be used for
    writing data sequentially to a container or to some output
    stream. It must provide the following operators: unary \c{*} for
    writing a value (i.e., \c{*it = val}) and prefix \c{++} for
    advancing to the next item.

    The Qt containers' non-const iterator types are all output
    iterators.

    \section2 Forward Iterators

    A \e{forward iterator} is an iterator that meets the requirements
    of both input iterators and output iterators.

    The Qt containers' non-const iterator types are all forward
    iterators.

    \section2 Bidirectional Iterators

    A \e{bidirectional iterator} is an iterator that meets the
    requirements of forward iterators but that in addition supports
    prefix \c{--} for iterating backward.

    The Qt containers' non-const iterator types are all bidirectional
    iterators.

    \section2 Random Access Iterators

    The last category, \e{random access iterators}, is the most
    powerful type of iterator. It supports all the requirements of a
    bidirectional iterator, and supports the following operations:

    \table
    \row \li \c{i += n} \li advances iterator \c i by \c n positions
    \row \li \c{i -= n} \li moves iterator \c i back by \c n positions
    \row \li \c{i + n} or \c{n + i} \li returns the iterator for the item \c
       n positions ahead of iterator \c i
    \row \li \c{i - n} \li returns the iterator for the item \c n positions behind of iterator \c i
    \row \li \c{i - j} \li returns the number of items between iterators \c i and \c j
    \row \li \c{i[n]} \li same as \c{*(i + n)}
    \row \li \c{i < j} \li returns \c true if iterator \c j comes after iterator \c i
    \endtable

    QList and QVector's non-const iterator types are random access iterators.

    \section1 Qt and the STL Algorithms

    Historically, Qt used to provide functions which were direct equivalents of
    many STL algorithmic functions. Starting with Qt 5.0, you are instead
    encouraged to use directly the implementations available in the STL; most
    of the Qt ones have been deprecated (although they are still available to
    keep the old code compiling).

    \section2 Porting guidelines

    Most of the time, an application using the deprecated Qt algorithmic functions
    can be easily ported to use the equivalent STL functions. You need to:

    \list 1
        \li add the \c{#include <algorithm>} preprocessor directive;
        \li replace the Qt functions with the STL counterparts, according to the table below.
    \endlist

    \table
    \header
        \li Qt function
        \li STL function
    \row
        \li qBinaryFind
        \li \c std::binary_search or \c std::lower_bound
    \row
        \li qCopy
        \li \c std::copy
    \row
        \li qCopyBackward
        \li \c std::copy_backward
    \row
        \li qEqual
        \li \c std::equal
    \row
        \li qFill
        \li \c std::fill
    \row
        \li qFind
        \li \c std::find
    \row
        \li qCount
        \li \c std::count
    \row
        \li qSort
        \li \c std::sort
    \row
        \li qStableSort
        \li \c std::stable_sort
    \row
        \li qLowerBound
        \li \c std::lower_bound
    \row
        \li qUpperBound
        \li \c std::upper_bound
    \row
        \li qLess
        \li \c std::less
    \row
        \li qGreater
        \li \c std::greater

    \endtable

    The only cases in which the port may not be straightforward is if the old
    code relied on template specializations of the qLess() and/or the qSwap()
    functions, which were used internally by the implementations of the Qt
    algorithmic functions, but are instead ignored by the STL ones.

    In case the old code relied on the specialization of the qLess() functor,
    then a workaround is explicitly passing an instance of the qLess() class
    to the STL function, for instance like this:

    \code
        std::sort(container.begin(), container.end(), qLess<T>());
    \endcode

    Instead, since it's not possible to pass a custom swapper functor to STL
    functions, the only workaround for a template specialization for qSwap() is
    providing the same specialization for \c std::swap().

    \sa {container classes}, <QtGlobal>
*/

/*! \fn template <typename InputIterator, typename OutputIterator> OutputIterator qCopy(InputIterator begin1, InputIterator end1, OutputIterator begin2)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::copy instead.

    Copies the items from range [\a begin1, \a end1) to range [\a
    begin2, ...), in the order in which they appear.

    The item at position \a begin1 is assigned to that at position \a
    begin2; the item at position \a begin1 + 1 is assigned to that at
    position \a begin2 + 1; and so on.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 4

    \sa qCopyBackward(), {input iterators}, {output iterators}
*/

/*! \fn template <typename BiIterator1, typename BiIterator2> BiIterator2 qCopyBackward(BiIterator1 begin1, BiIterator1 end1, BiIterator2 end2)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::copy_backward instead.

    Copies the items from range [\a begin1, \a end1) to range [...,
    \a end2).

    The item at position \a end1 - 1 is assigned to that at position
    \a end2 - 1; the item at position \a end1 - 2 is assigned to that
    at position \a end2 - 2; and so on.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 5

    \sa qCopy(), {bidirectional iterators}
*/

/*! \fn template <typename InputIterator1, typename InputIterator2> bool qEqual(InputIterator1 begin1, InputIterator1 end1, InputIterator2 begin2)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::equal instead.

    Compares the items in the range [\a begin1, \a end1) with the
    items in the range [\a begin2, ...). Returns \c true if all the
    items compare equal; otherwise returns \c false.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 6

    This function requires the item type (in the example above,
    QString) to implement \c operator==().

    \sa {input iterators}
*/

/*! \fn template <typename ForwardIterator, typename T> void qFill(ForwardIterator begin, ForwardIterator end, const T &value)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::fill instead.

    Fills the range [\a begin, \a end) with \a value.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 7

    \sa qCopy(), {forward iterators}
*/

/*! \fn template <typename Container, typename T> void qFill(Container &container, const T &value)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::fill instead.

    This is the same as qFill(\a{container}.begin(), \a{container}.end(), \a value);
*/

/*! \fn template <typename InputIterator, typename T> InputIterator qFind(InputIterator begin, InputIterator end, const T &value)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::find instead.

    Returns an iterator to the first occurrence of \a value in a
    container in the range [\a begin, \a end). Returns \a end if \a
    value isn't found.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 8

    This function requires the item type (in the example above,
    QString) to implement \c operator==().

    If the items in the range are in ascending order, you can get
    faster results by using qLowerBound() or qBinaryFind() instead of
    qFind().

    \sa qBinaryFind(), {input iterators}
*/

/*! \fn template <typename Container, typename T> void qFind(const Container &container, const T &value)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::find instead.

    This is the same as qFind(\a{container}.constBegin(), \a{container}.constEnd(), \a value);
*/

/*! \fn template <typename InputIterator, typename T, typename Size> void qCount(InputIterator begin, InputIterator end, const T &value, Size &n)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::count instead.

    Returns the number of occurrences of \a value in the range [\a begin, \a end),
    which is returned in \a n. \a n is never initialized, the count is added to \a n.
    It is the caller's responsibility to initialize \a n.

    Example:

    \snippet code/doc_src_qalgorithms.cpp 9

    This function requires the item type (in the example above,
    \c int) to implement \c operator==().

    \sa {input iterators}
*/

/*! \fn template <typename Container, typename T, typename Size> void qCount(const Container &container, const T &value, Size &n)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::count instead.

    Instead of operating on iterators, as in the other overload, this function
    operates on the specified \a container to obtain the number of instances
    of \a value in the variable passed as a reference in argument \a n.
*/

/*! \fn template <typename T> void qSwap(T &var1, T &var2)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::swap instead.

    Exchanges the values of variables \a var1 and \a var2.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 10
*/

/*! \fn template <typename RandomAccessIterator> void qSort(RandomAccessIterator begin, RandomAccessIterator end)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::sort instead.

    Sorts the items in range [\a begin, \a end) in ascending order
    using the quicksort algorithm.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 11

    The sort algorithm is efficient on large data sets. It operates
    in \l {linear-logarithmic time}, O(\e{n} log \e{n}).

    This function requires the item type (in the example above,
    \c{int}) to implement \c operator<().

    If neither of the two items is "less than" the other, the items are
    taken to be equal. It is then undefined which one of the two
    items will appear before the other after the sort.

    \sa qStableSort(), {random access iterators}
*/

/*! \fn template <typename RandomAccessIterator, typename LessThan> void qSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::sort instead.

    Uses the \a lessThan function instead of \c operator<() to
    compare the items.

    For example, here's how to sort the strings in a QStringList
    in case-insensitive alphabetical order:

    \snippet code/doc_src_qalgorithms.cpp 12

    To sort values in reverse order, pass
    \l{qGreater()}{qGreater<T>()} as the \a lessThan parameter. For
    example:

    \snippet code/doc_src_qalgorithms.cpp 13

    If neither of the two items is "less than" the other, the items are
    taken to be equal. It is then undefined which one of the two
    items will appear before the other after the sort.

    An alternative to using qSort() is to put the items to sort in a
    QMap, using the sort key as the QMap key. This is often more
    convenient than defining a \a lessThan function. For example, the
    following code shows how to sort a list of strings case
    insensitively using QMap:

    \snippet code/doc_src_qalgorithms.cpp 14

    \sa QMap
*/

/*! \fn template<typename Container> void qSort(Container &container)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::sort instead.

    This is the same as qSort(\a{container}.begin(), \a{container}.end());
*/

/*!
    \fn template <typename RandomAccessIterator> void qStableSort(RandomAccessIterator begin, RandomAccessIterator end)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::stable_sort instead.

    Sorts the items in range [\a begin, \a end) in ascending order
    using a stable sorting algorithm.

    If neither of the two items is "less than" the other, the items are
    taken to be equal. The item that appeared before the other in the
    original container will still appear first after the sort. This
    property is often useful when sorting user-visible data.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 15

    The sort algorithm is efficient on large data sets. It operates
    in \l {linear-logarithmic time}, O(\e{n} log \e{n}).

    This function requires the item type (in the example above,
    \c{int}) to implement \c operator<().

    \sa qSort(), {random access iterators}
*/

/*!
    \fn template <typename RandomAccessIterator, typename LessThan> void qStableSort(RandomAccessIterator begin, RandomAccessIterator end, LessThan lessThan)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::stable_sort instead.

    Uses the \a lessThan function instead of \c operator<() to
    compare the items.

    For example, here's how to sort the strings in a QStringList
    in case-insensitive alphabetical order:

    \snippet code/doc_src_qalgorithms.cpp 16

    Note that earlier versions of Qt allowed using a lessThan function that took its
    arguments by non-const reference. From 4.3 and on this is no longer possible,
    the arguments has to be passed by const reference or value.

    To sort values in reverse order, pass
    \l{qGreater()}{qGreater<T>()} as the \a lessThan parameter. For
    example:

    \snippet code/doc_src_qalgorithms.cpp 17

    If neither of the two items is "less than" the other, the items are
    taken to be equal. The item that appeared before the other in the
    original container will still appear first after the sort. This
    property is often useful when sorting user-visible data.
*/

/*!
    \fn template <typename Container> void qStableSort(Container &container)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::stable_sort instead.

    This is the same as qStableSort(\a{container}.begin(), \a{container}.end());
*/

/*! \fn template <typename RandomAccessIterator, typename T> RandomAccessIterator qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::lower_bound instead.

    Performs a binary search of the range [\a begin, \a end) and
    returns the position of the first occurrence of \a value. If no
    such item is found, returns the position where it should be
    inserted.

    The items in the range [\a begin, \e end) must be sorted in
    ascending order; see qSort().

    Example:
    \snippet code/doc_src_qalgorithms.cpp 18

    This function requires the item type (in the example above,
    \c{int}) to implement \c operator<().

    qLowerBound() can be used in conjunction with qUpperBound() to
    iterate over all occurrences of the same value:

    \snippet code/doc_src_qalgorithms.cpp 19

    \sa qUpperBound(), qBinaryFind()
*/

/*!
    \fn template <typename RandomAccessIterator, typename T, typename LessThan> RandomAccessIterator qLowerBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::lower_bound instead.

    Uses the \a lessThan function instead of \c operator<() to
    compare the items.

    Note that the items in the range must be sorted according to the order
    specified by the \a lessThan object.
*/

/*!
    \fn template <typename Container, typename T> void qLowerBound(const Container &container, const T &value)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::lower_bound instead.

    For read-only iteration over containers, this function is broadly equivalent to
    qLowerBound(\a{container}.begin(), \a{container}.end(), value). However, since it
    returns a const iterator, you cannot use it to modify the container; for example,
    to insert items.
*/

/*! \fn template <typename RandomAccessIterator, typename T> RandomAccessIterator qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::upper_bound instead.

    Performs a binary search of the range [\a begin, \a end) and
    returns the position of the one-past-the-last occurrence of \a
    value. If no such item is found, returns the position where the
    item should be inserted.

    The items in the range [\a begin, \e end) must be sorted in
    ascending order; see qSort().

    Example:
    \snippet code/doc_src_qalgorithms.cpp 20

    This function requires the item type (in the example above,
    \c{int}) to implement \c operator<().

    qUpperBound() can be used in conjunction with qLowerBound() to
    iterate over all occurrences of the same value:

    \snippet code/doc_src_qalgorithms.cpp 21

    \sa qLowerBound(), qBinaryFind()
*/

/*!
    \fn template <typename RandomAccessIterator, typename T, typename LessThan> RandomAccessIterator qUpperBound(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::upper_bound instead.

    Uses the \a lessThan function instead of \c operator<() to
    compare the items.

    Note that the items in the range must be sorted according to the order
    specified by the \a lessThan object.
*/

/*!
    \fn template <typename Container, typename T> void qUpperBound(const Container &container, const T &value)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::upper_bound instead.

    This is the same as qUpperBound(\a{container}.begin(), \a{container}.end(), \a value);
*/


/*! \fn template <typename RandomAccessIterator, typename T> RandomAccessIterator qBinaryFind(RandomAccessIterator begin, RandomAccessIterator end, const T &value)
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::binary_search or \c std::lower_bound instead.

    Performs a binary search of the range [\a begin, \a end) and
    returns the position of an occurrence of \a value. If there are
    no occurrences of \a value, returns \a end.

    The items in the range [\a begin, \a end) must be sorted in
    ascending order; see qSort().

    If there are many occurrences of the same value, any one of them
    could be returned. Use qLowerBound() or qUpperBound() if you need
    finer control.

    Example:
    \snippet code/doc_src_qalgorithms.cpp 22

    This function requires the item type (in the example above,
    QString) to implement \c operator<().

    \sa qLowerBound(), qUpperBound(), {random access iterators}
*/

/*! \fn template <typename RandomAccessIterator, typename T, typename LessThan> RandomAccessIterator qBinaryFind(RandomAccessIterator begin, RandomAccessIterator end, const T &value, LessThan lessThan)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::binary_search or \c std::lower_bound instead.

    Uses the \a lessThan function instead of \c operator<() to
    compare the items.

    Note that the items in the range must be sorted according to the order
    specified by the \a lessThan object.
*/

/*!
    \fn template <typename Container, typename T> void qBinaryFind(const Container &container, const T &value)
    \relates <QtAlgorithms>
    \deprecated
    \overload

    Use \c std::binary_search or \c std::lower_bound instead.

    This is the same as qBinaryFind(\a{container}.begin(), \a{container}.end(), \a value);
*/


/*!
    \fn template <typename ForwardIterator> void qDeleteAll(ForwardIterator begin, ForwardIterator end)
    \relates <QtAlgorithms>

    Deletes all the items in the range [\a begin, \a end) using the
    C++ \c delete operator. The item type must be a pointer type (for
    example, \c{QWidget *}).

    Example:
    \snippet code/doc_src_qalgorithms.cpp 23

    Notice that qDeleteAll() doesn't remove the items from the
    container; it merely calls \c delete on them. In the example
    above, we call clear() on the container to remove the items.

    This function can also be used to delete items stored in
    associative containers, such as QMap and QHash. Only the objects
    stored in each container will be deleted by this function; objects
    used as keys will not be deleted.

    \sa {forward iterators}
*/

/*!
    \fn template <typename Container> void qDeleteAll(const Container &c)
    \relates <QtAlgorithms>

    \overload

    This is the same as qDeleteAll(\a{c}.begin(), \a{c}.end()).
*/

/*! \fn template <typename LessThan> LessThan qLess()
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::less instead.

    Returns a functional object, or functor, that can be passed to qSort()
    or qStableSort().

    Example:

    \snippet code/doc_src_qalgorithms.cpp 24

    \sa {qGreater()}{qGreater<T>()}
*/

/*! \fn template <typename LessThan> LessThan qGreater()
    \relates <QtAlgorithms>
    \deprecated

    Use \c std::greater instead.

    Returns a functional object, or functor, that can be passed to qSort()
    or qStableSort().

    Example:

    \snippet code/doc_src_qalgorithms.cpp 25

    \sa {qLess()}{qLess<T>()}
*/


/*!
    \fn uint qPopulationCount(quint8 v)
    \relates <QtAlgorithms>
    \since 5.2

    Returns the number of bits set in \a v. This number is also called
    the Hamming Weight of \a v.
 */

/*!
    \fn uint qPopulationCount(quint16 v)
    \relates <QtAlgorithms>
    \since 5.2
    \overload
 */

/*!
    \fn uint qPopulationCount(quint32 v)
    \relates <QtAlgorithms>
    \since 5.2
    \overload
 */

/*!
    \fn uint qPopulationCount(quint64 v)
    \relates <QtAlgorithms>
    \since 5.2
    \overload
 */

/*!
    \fn uint qCountTrailingZeroBits(quint8 v)
    \relates <QtAlgorithms>
    \since 5.6

    Returns the number of consecutive zero bits in \a v, when searching from the LSB.
    For example, qCountTrailingZeroBits(1) returns 0 and qCountTrailingZeroBits(8) returns 3.
 */

/*!
    \fn uint qCountTrailingZeroBits(quint16 v)
    \relates <QtAlgorithms>
    \since 5.6
    \overload
 */

/*!
    \fn uint qCountTrailingZeroBits(quint32 v)
    \relates <QtAlgorithms>
    \since 5.6
    \overload
 */

/*!
    \fn uint qCountTrailingZeroBits(quint64 v)
    \relates <QtAlgorithms>
    \since 5.6
    \overload
 */

/*!
    \fn uint qCountLeadingZeroBits(quint8 v)
    \relates <QtAlgorithms>
    \since 5.6

    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint8(1)) returns 7 and
    qCountLeadingZeroBits(quint8(8)) returns 4.
 */

/*!
    \fn uint qCountLeadingZeroBits(quint16 v)
    \relates <QtAlgorithms>
    \since 5.6

    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint16(1)) returns 15 and
    qCountLeadingZeroBits(quint16(8)) returns 12.
 */

/*!
    \fn uint qCountLeadingZeroBits(quint32 v)
    \relates <QtAlgorithms>
    \since 5.6

    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint32(1)) returns 31 and
    qCountLeadingZeroBits(quint32(8)) returns 28.
 */

/*!
    \fn uint qCountLeadingZeroBits(quint64 v)
    \relates <QtAlgorithms>
    \since 5.6

    Returns the number of consecutive zero bits in \a v, when searching from the MSB.
    For example, qCountLeadingZeroBits(quint64(1)) returns 63 and
    qCountLeadingZeroBits(quint64(8)) returns 60.
 */