STL sort源码剖析

来源：互联网发布：淘宝购买魔术道具编辑：程序博客网时间：2024/04/28 23:13

//sort函数源码：

template <class _RandomAccessIter>inline void sort(_RandomAccessIter __first, _RandomAccessIter __last) {  __STL_REQUIRES(_RandomAccessIter, _Mutable_RandomAccessIterator);  __STL_REQUIRES(typename iterator_traits<_RandomAccessIter>::value_type,                 _LessThanComparable);  if (__first != __last) { //如果待排序序列非空;    //进行introsort排序,其中__lg函数用于控制最大分割层数;    __introsort_loop(__first, __last,                     __VALUE_TYPE(__first),                     __lg(__last - __first) * 2);    __final_insertion_sort(__first, __last);//对序列进行插入排序;  }}

//__lg函数源码：

//找出2^k<=n的最大值k；template <class _Size>inline _Size __lg(_Size __n) {  _Size __k;  for (__k = 0; __n != 1; __n >>= 1) ++__k;  return __k;}

//__introsort_loop函数源码:

const int __stl_threshold = 16; //全局变量;template <class _RandomAccessIter, class _Tp, class _Size>//_Tp为待排序元素类型, __depth_limit为最多允许分割的层数;void __introsort_loop(_RandomAccessIter __first,                      _RandomAccessIter __last, _Tp*,                      _Size __depth_limit){  while (__last - __first > __stl_threshold) {//如果待排序元素个数大于阀值;    if (__depth_limit == 0) {//如果允许分割层数为0;      partial_sort(__first, __last, __last);//对[first,last)进行堆排序;      return;    }    --__depth_limit;//分割层数减1;    //__median函数用于选择一个枢轴，然后进行一次分割操作,其中cut为"右半段"的第一个元素;    _RandomAccessIter __cut =      __unguarded_partition(__first, __last,                            _Tp(__median(*__first,                                         *(__first + (__last - __first)/2),                                         *(__last - 1))));    __introsort_loop(__cut, __last, (_Tp*) 0, __depth_limit);//对"右半段"进行__introsort排序;    __last = __cut;//继续while循环,对由[first,last)表示的"左半段"进行introsort；  }}

//__unguarded_paririon函数源码:

template <class _RandomAccessIter, class _Tp>_RandomAccessIter __unguarded_partition(_RandomAccessIter __first,                                         _RandomAccessIter __last,                                         _Tp __pivot) //分割函数;{  while (true) {    while (*__first < __pivot)//如果first指向的元素小于枢轴;      ++__first;    --__last;    while (__pivot < *__last)//如果枢轴小于last指向的元素;      --__last;    if (!(__first < __last))//如果first和last迭代器交错，first为右半段第一个元素;      return __first;    iter_swap(__first, __last);//firtst和last指向的元素交换;    ++__first;  }}

//partial_sort函数源码:

template <class _RandomAccessIter>inline void partial_sort(_RandomAccessIter __first,                         _RandomAccessIter __middle,                         _RandomAccessIter __last) {  __STL_REQUIRES(_RandomAccessIter, _Mutable_RandomAccessIterator);  __STL_REQUIRES(typename iterator_traits<_RandomAccessIter>::value_type,                 _LessThanComparable);  __partial_sort(__first, __middle, __last, __VALUE_TYPE(__first));}template <class _RandomAccessIter, class _Tp>void __partial_sort(_RandomAccessIter __first, _RandomAccessIter __middle,                    _RandomAccessIter __last, _Tp*) {  make_heap(__first, __middle);//建立大顶堆;  //分割[middle,last)为[first,last)的"右半段";  for (_RandomAccessIter __i = __middle; __i < __last; ++__i)    if (*__i < *__first)       __pop_heap(__first, __middle, __i, _Tp(*__i),                 __DISTANCE_TYPE(__first));  sort_heap(__first, __middle);//对[first,middle)区间(即左半段)进行堆排序;}

// __final_insertion_sort函数源码:

//进行插入排序;void __final_insertion_sort(_RandomAccessIter __first,                             _RandomAccessIter __last) {  if (__last - __first > __stl_threshold) {    __insertion_sort(__first, __first + __stl_threshold);    __unguarded_insertion_sort(__first + __stl_threshold, __last);  }  else    __insertion_sort(__first, __last);}

//__insertion_sort函数源码:

template <class _RandomAccessIter>void __insertion_sort(_RandomAccessIter __first, _RandomAccessIter __last) {  if (__first == __last) return;   for (_RandomAccessIter __i = __first + 1; __i != __last; ++__i)    __linear_insert(__first, __i, __VALUE_TYPE(__first));}template <class _RandomAccessIter, class _Tp>inline void __linear_insert(_RandomAccessIter __first,                             _RandomAccessIter __last, _Tp*) {  _Tp __val = *__last;  if (__val < *__first) {    copy_backward(__first, __last, __last + 1);    *__first = __val;  }  else    __unguarded_linear_insert(__last, __val);}template <class _RandomAccessIter, class _Tp>void __unguarded_linear_insert(_RandomAccessIter __last, _Tp __val) {  _RandomAccessIter __next = __last;  --__next;  while (__val < *__next) {    *__last = *__next;    __last = __next;    --__next;  }  *__last = __val;}

//__unguarded_insertion_sort函数源码:

template <class _RandomAccessIter>inline void __unguarded_insertion_sort(_RandomAccessIter __first,                                 _RandomAccessIter __last) {  __unguarded_insertion_sort_aux(__first, __last, __VALUE_TYPE(__first));}template <class _RandomAccessIter, class _Tp>void __unguarded_insertion_sort_aux(_RandomAccessIter __first,                                     _RandomAccessIter __last, _Tp*) {  for (_RandomAccessIter __i = __first; __i != __last; ++__i)    __unguarded_linear_insert(__i, _Tp(*__i));}

//参考文献《STL源码剖析》

0 0