《STL源碼剖析》---stl_numeric.h閱讀筆記

標籤：c++   源碼   數值演算法   

stl_numeric.h裡面的都是數值演算法，與數值計算有關。

G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_numeric.h 完整列表/* * * Copyright (c) 1994 * Hewlett-Packard Company * * Permission to use, copy, modify, distribute and sell this software * and its documentation for any purpose is hereby granted without fee, * provided that the above copyright notice appear in all copies and * that both that copyright notice and this permission notice appear * in supporting documentation.  Hewlett-Packard Company makes no * representations about the suitability of this software for any * purpose.  It is provided "as is" without express or implied warranty. * * * Copyright (c) 1996,1997 * Silicon Graphics Computer Systems, Inc. * * Permission to use, copy, modify, distribute and sell this software * and its documentation for any purpose is hereby granted without fee, * provided that the above copyright notice appear in all copies and * that both that copyright notice and this permission notice appear * in supporting documentation.  Silicon Graphics makes no * representations about the suitability of this software for any * purpose.  It is provided "as is" without express or implied warranty. *//* NOTE: This is an internal header file, included by other STL headers. *   You should not attempt to use it directly. */#ifndef __SGI_STL_INTERNAL_NUMERIC_H#define __SGI_STL_INTERNAL_NUMERIC_H__STL_BEGIN_NAMESPACE//計算init和[first last)區間元素的和// 版本一template <class InputIterator, class T>T accumulate(InputIterator first, InputIterator last, T init) {  for ( ; first != last; ++first)    init = init + *first; // 每個元素的初值累加到init上  return init;}// 版本二template <class InputIterator, class T, class BinaryOperation>T accumulate(InputIterator first, InputIterator last, T init,                BinaryOperation binary_op) {  for ( ; first != last; ++first)    init = binary_op(init, *first);//  對每一個元素執行二元操作  return init;}//計算兩段元素的內積，要提供初始值init。兩段元素一樣長，所以第二段沒提供last2// 版本一template <class InputIterator1, class InputIterator2, class T>T inner_product(InputIterator1 first1, InputIterator1 last1,                   InputIterator2 first2, T init) {  for ( ; first1 != last1; ++first1, ++first2)    init = init + (*first1 * *first2); // 執行兩個序列的一般內積  return init;}// 版本二template <class InputIterator1, class InputIterator2, class T,          class BinaryOperation1, class BinaryOperation2>T inner_product(InputIterator1 first1, InputIterator1 last1,                   InputIterator2 first2, T init, BinaryOperation1 binary_op1,                   BinaryOperation2 binary_op2) {  for ( ; first1 != last1; ++first1, ++first2)// 以外界提供的仿函數來取代第一版本中的 operator* 和 operator+。// op2 範圍兩元素間，op1用於op2之結果與init之間。    init = binary_op1(init, binary_op2(*first1, *first2));  return init;}//__partial_sum定義在partial_sum前面，後者調用前者template <class InputIterator, class OutputIterator, class T>OutputIterator __partial_sum(InputIterator first, InputIterator last,                                   OutputIterator result, T*) {  T value = *first;  while (++first != last) {    value = value + *first; // 前n個元素的總和    *++result = value;// 指定給目的端  }  return ++result;}// 版本一template <class InputIterator, class OutputIterator>OutputIterator partial_sum(InputIterator first, InputIterator last,                                OutputIterator result) {  if (first == last) return result;  *result = *first;  return __partial_sum(first, last, result, value_type(first));  // 侯捷認為（並證實證），不需像上行那樣轉呼叫，可改用以下寫法（整個函式）：  // if (first == last) return result;  // *result = *first;  // iterator_traits<InputIterator>::value_type value = *first;  // while (++first != last) {  //   value = value + *first;  //   *++result = value;  // }  // return ++result;  // 這樣的觀念和作法，適用於本當所有函數}template <class InputIterator, class OutputIterator, class T,          class BinaryOperation>OutputIterator __partial_sum(InputIterator first, InputIterator last,                                  OutputIterator result, T*,                                  BinaryOperation binary_op) {  T value = *first;  while (++first != last) {    value = binary_op(value, *first);    *++result = value;  }  return ++result;}// 版本二template <class InputIterator, class OutputIterator, class BinaryOperation>OutputIterator partial_sum(InputIterator first, InputIterator last,                                OutputIterator result, BinaryOperation binary_op) {  if (first == last) return result;  *result = *first;  return __partial_sum(first, last, result, value_type(first), binary_op);  //  侯捷認為（並證實證），不需像上行那樣轉呼叫，可改用以下寫法（整個函式）：  // if (first == last) return result;  // *result = *first;  // iterator_trait<InputIterator>::value_type value = *first;  // while (++first != last) {  //   value = binary_op(value, *first);  //   *++result = value;  // }  // return ++result;  //  //  這樣的觀念和作法，適用於本當所有函數}template <class InputIterator, class OutputIterator, class T>OutputIterator __adjacent_difference(InputIterator first, InputIterator last,                                             OutputIterator result, T*) {  T value = *first;  while (++first != last) {// 走過整個範圍    T tmp = *first;    *++result = tmp - value;// 將兩個相鄰元素的差額（後-前），指派給目的端    value = tmp;  }  return ++result;}// 版本一template <class InputIterator, class OutputIterator>OutputIterator adjacent_difference(InputIterator first, InputIterator last,                                           OutputIterator result) {  if (first == last) return result;  *result = *first;// 首先記錄第一個元素  return __adjacent_difference(first, last, result, value_type(first));}template <class InputIterator, class OutputIterator, class T,           class BinaryOperation>OutputIterator __adjacent_difference(InputIterator first, InputIterator last,                                             OutputIterator result, T*,                                            BinaryOperation binary_op) {  T value = *first;  while (++first != last) {    T tmp = *first;    *++result = binary_op(tmp, value); // 將相鄰兩元素的運算結果，指派給目的端    value = tmp;  }  return ++result;}// 版本二template <class InputIterator, class OutputIterator, class BinaryOperation>OutputIterator adjacent_difference(InputIterator first, InputIterator last,                                          OutputIterator result,                                          BinaryOperation binary_op) {  if (first == last) return result;  *result = *first;  return __adjacent_difference(first, last, result, value_type(first),                                     binary_op);}//power為SGI專屬，並不在STL標準之列，它用來計算某數的n冪次方。//這裡所謂的n冪次方是指對自己進行某種運算n次，運算類型可由外界執行。如果是乘法則就是乘冪。// 版本二，冪次方。如果指定為乘法運算，則當n >= 0 時傳回 x ** n。// 注意，"multiplication" 必須滿足結合律（associative），//  但不需滿足交換律（commutative）。template <class T, class Integer, class MonoidOperation>T power(T x, Integer n, MonoidOperation op) {  if (n == 0)    return identity_element(op);// 取出「證同元素」identity element.證同元素在後面章節介紹  else {    while ((n & 1) == 0) {      n >>= 1;      x = op(x, x);//兩個參數都是x。因為每次n減小1倍(n是偶數，因為n&1=0)    }    T result = x;    n >>= 1;    while (n != 0) {      x = op(x, x);      if ((n & 1) != 0)        result = op(result, x);      n >>= 1;    }    return result;  }}// 版本一，乘冪。template <class T, class Integer>inline T power(T x, Integer n) {  return power(x, n, multiplies<T>());}// 侯捷：iota 是什麼的縮寫？// 函數意義：在 [first,last) 範圍內內填入value, value+1, value+2...。template <class ForwardIterator, class T>void iota(ForwardIterator first, ForwardIterator last, T value) {  while (first != last) *first++ = value++;}__STL_END_NAMESPACE#endif /* __SGI_STL_INTERNAL_NUMERIC_H */// Local Variables:// mode:C++// End: