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minmax_element: reduce complexity

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This commit is contained in:
Mitsuru Kariya 2015-02-15 15:14:26 +09:00
parent 586c9972dc
commit 09f8215195
1 changed files with 73 additions and 15 deletions
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86
sprout/algorithm/minmax_element.hpp
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@ -35,28 +35,37 @@ namespace sprout {
comp(*b, *sprout::second(a)) ? sprout::second(a) : b
);
}
template<typename ForwardIterator, typename Compare>
inline SPROUT_CONSTEXPR sprout::pair<ForwardIterator, ForwardIterator>
iter_minmax(ForwardIterator a, ForwardIterator b, Compare comp) {
typedef sprout::pair<ForwardIterator, ForwardIterator> type;
return comp(*b, *a)
? type(b, a)
: type(a, b)
;
}
template<typename RandomAccessIterator, typename Compare>
inline SPROUT_CONSTEXPR sprout::pair<RandomAccessIterator, RandomAccessIterator>
minmax_element_impl_ra(
RandomAccessIterator first, RandomAccessIterator last, Compare comp,
typename std::iterator_traits<RandomAccessIterator>::difference_type pivot
RandomAccessIterator first, Compare comp,
typename std::iterator_traits<RandomAccessIterator>::difference_type half
)
{
return pivot == 0 ? sprout::pair<RandomAccessIterator, RandomAccessIterator>(first, first)
return half == 1
? iter_minmax(first, sprout::next(first), comp)
: sprout::detail::iter_minmax_pair(
sprout::detail::minmax_element_impl_ra(
first, sprout::next(first, pivot), comp,
pivot / 2
first, comp, half / 2
),
sprout::detail::minmax_element_impl_ra(
sprout::next(first, pivot), last, comp,
(sprout::distance(first, last) - pivot) / 2
sprout::next(first, half - (half & 1)), comp, (half + 1) / 2
),
comp
)
;
}
template<typename RandomAccessIterator, typename Compare>
inline SPROUT_CONSTEXPR typename std::enable_if<
sprout::is_constant_distance_iterator<RandomAccessIterator>::value,
@ -67,11 +76,44 @@ namespace sprout {
std::random_access_iterator_tag*
)
{
return first == last ? sprout::pair<RandomAccessIterator, RandomAccessIterator>(last, last)
: sprout::detail::minmax_element_impl_ra(
first, last, comp,
return first == last || sprout::next(first) == last
? sprout::pair<RandomAccessIterator, RandomAccessIterator>(first, first)
: sprout::distance(first, last) % 2 == 0
? sprout::detail::minmax_element_impl_ra(
first, comp,
sprout::distance(first, last) / 2
)
: sprout::detail::iter_minmax(
sprout::detail::minmax_element_impl_ra(
first, comp,
sprout::distance(first, last) / 2
),
sprout::prev(last),
comp
)
;
}
template<typename ForwardIterator, typename Compare>
inline SPROUT_CONSTEXPR sprout::pair<ForwardIterator, sprout::pair<ForwardIterator, ForwardIterator> >
minmax_element_impl_3(
sprout::pair<ForwardIterator, ForwardIterator> minmax,
ForwardIterator first, ForwardIterator next,
ForwardIterator last, Compare comp) {
typedef sprout::pair<ForwardIterator, sprout::pair<ForwardIterator, ForwardIterator> > type;
return next == last
? type(
next,
sprout::detail::iter_minmax(minmax, first, comp)
)
: type(
sprout::next(next),
sprout::detail::iter_minmax_pair(
minmax,
sprout::detail::iter_minmax(first, next, comp),
comp
)
)
;
}
@ -82,9 +124,10 @@ namespace sprout {
ForwardIterator last, Compare comp, typename std::iterator_traits<ForwardIterator>::difference_type n
)
{
typedef sprout::pair<ForwardIterator, sprout::pair<ForwardIterator, ForwardIterator> > type;
return current.first == last ? current
: n == 1 ? type(sprout::next(current.first), sprout::detail::iter_minmax(current.second, current.first, comp))
: n == 1 ? sprout::detail::minmax_element_impl_3(
current.second, current.first, sprout::next(current.first),
last, comp)
: sprout::detail::minmax_element_impl_1(
sprout::detail::minmax_element_impl_1(
current,
@ -94,6 +137,7 @@ namespace sprout {
)
;
}
template<typename ForwardIterator, typename Compare>
inline SPROUT_CONSTEXPR sprout::pair<ForwardIterator, sprout::pair<ForwardIterator, ForwardIterator> >
minmax_element_impl(
@ -111,6 +155,19 @@ namespace sprout {
)
;
}
template<typename ForwardIterator, typename Compare>
inline SPROUT_CONSTEXPR sprout::pair<ForwardIterator, sprout::pair<ForwardIterator, ForwardIterator> >
minmax_element_impl_2(
ForwardIterator first, ForwardIterator next, ForwardIterator last, Compare comp
)
{
typedef sprout::pair<ForwardIterator, ForwardIterator> type;
return next == last ? sprout::pair<ForwardIterator, type>(next, type(first, first))
: sprout::pair<ForwardIterator, type>(sprout::next(next), iter_minmax(first, next, comp))
;
}
template<typename ForwardIterator, typename Compare>
inline SPROUT_CONSTEXPR sprout::pair<ForwardIterator, ForwardIterator>
minmax_element(
@ -118,9 +175,10 @@ namespace sprout {
std::forward_iterator_tag*
)
{
typedef sprout::pair<ForwardIterator, sprout::pair<ForwardIterator, ForwardIterator> > type;
return first == last ? sprout::pair<ForwardIterator, ForwardIterator>(first, first)
: sprout::detail::minmax_element_impl(type(sprout::next(first), sprout::pair<ForwardIterator, ForwardIterator>(first, first)), last, comp, 1).second
: sprout::detail::minmax_element_impl(
sprout::detail::minmax_element_impl_2(first, sprout::next(first), last, comp),
last, comp, 1).second
;
}
} // namespace detail