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Demonstrates a version of std::copy
that uses has_trivial_assign
to
determine whether to use memcpy
to optimise the copy operation
(see copy_example.cpp):
//
// opt::copy
// same semantics as std::copy
// calls memcpy where appropriate.
//
namespace detail{
template<typename I1, typename I2, bool b>
I2 copy_imp(I1 first, I1 last, I2 out, const boost::integral_constant<bool, b>&)
{
while(first != last)
{
*out = *first;
++out;
++first;
}
return out;
}
template<typename T>
T* copy_imp(const T* first, const T* last, T* out, const boost::true_type&)
{
memcpy(out, first, (last-first)*sizeof(T));
return out+(last-first);
}
}
template<typename I1, typename I2>
inline I2 copy(I1 first, I1 last, I2 out)
{
//
// We can copy with memcpy if T has a trivial assignment operator,
// and if the iterator arguments are actually pointers (this last
// requirement we detect with overload resolution):
//
typedef typename std::iterator_traits<I1>::value_type value_type;
return detail::copy_imp(first, last, out, boost::has_trivial_assign<value_type>());
}
Demonstrates a version of std::fill
that uses has_trivial_assign
to
determine whether to use memset
to optimise the fill operation
(see fill_example.cpp):
//
// fill
// same as std::fill, but uses memset where appropriate
//
namespace detail{
template <typename I, typename T, bool b>
void do_fill(I first, I last, const T& val, const boost::integral_constant<bool, b>&)
{
while(first != last)
{
*first = val;
++first;
}
}
template <typename T>
void do_fill(T* first, T* last, const T& val, const boost::true_type&)
{
std::memset(first, val, last-first);
}
}
template <class I, class T>
inline void fill(I first, I last, const T& val)
{
//
// We can do an optimised fill if T has a trivial assignment
// operator and if it's size is one:
//
typedef boost::integral_constant<bool,
::boost::has_trivial_assign<T>::value && (sizeof(T) == 1)> truth_type;
detail::do_fill(first, last, val, truth_type());
}
Demonstrates a simple algorithm that uses __has_trivial_destruct
to
determine whether to destructors need to be called
(see trivial_destructor_example.cpp):
//
// algorithm destroy_array:
// The reverse of std::unitialized_copy, takes a block of
// initialized memory and calls destructors on all objects therein.
//
namespace detail{
template <class T>
void do_destroy_array(T* first, T* last, const boost::false_type&)
{
while(first != last)
{
first->~T();
++first;
}
}
template <class T>
inline void do_destroy_array(T* first, T* last, const boost::true_type&)
{
}
} // namespace detail
template <class T>
inline void destroy_array(T* p1, T* p2)
{
detail::do_destroy_array(p1, p2, ::boost::has_trivial_destructor<T>());
}
Demonstrates a version of std::iter_swap
that use type traits to
determine whether an it's arguments are proxying iterators or not,
if they're not then it just does a std::swap
of it's dereferenced
arguments (the
same as std::iter_swap
does), however if they are proxying iterators
then takes special care over the swap to ensure that the algorithm
works correctly for both proxying iterators, and even iterators of
different types
(see iter_swap_example.cpp):
//
// iter_swap:
// tests whether iterator is a proxying iterator or not, and
// uses optimal form accordingly:
//
namespace detail{
template <typename I>
static void do_swap(I one, I two, const boost::false_type&)
{
typedef typename std::iterator_traits<I>::value_type v_t;
v_t v = *one;
*one = *two;
*two = v;
}
template <typename I>
static void do_swap(I one, I two, const boost::true_type&)
{
using std::swap;
swap(*one, *two);
}
}
template <typename I1, typename I2>
inline void iter_swap(I1 one, I2 two)
{
//
// See is both arguments are non-proxying iterators,
// and if both iterator the same type:
//
typedef typename std::iterator_traits<I1>::reference r1_t;
typedef typename std::iterator_traits<I2>::reference r2_t;
typedef boost::integral_constant<bool,
::boost::is_reference<r1_t>::value
&& ::boost::is_reference<r2_t>::value
&& ::boost::is_same<r1_t, r2_t>::value> truth_type;
detail::do_swap(one, two, truth_type());
}
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