整理

include/boost/algorithm/algorithm.hpp

@@ -0,0 +1,89 @@
+/* 
+   Copyright (c) Marshall Clow 2014.
+
+   Distributed under the Boost Software License, Version 1.0. (See accompanying
+   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+ Revision history:
+    2 Dec 2014 mtc First version; power
+   
+*/
+
+/// \file algorithm.hpp
+/// \brief Misc Algorithms
+/// \author Marshall Clow
+///
+
+#ifndef BOOST_ALGORITHM_HPP
+#define BOOST_ALGORITHM_HPP
+
+#include <functional> // for plus and multiplies
+
+#include <boost/config.hpp>
+#include <boost/core/enable_if.hpp> // for boost::disable_if
+#include <boost/type_traits/is_integral.hpp>
+
+namespace boost { namespace algorithm {
+
+template <typename T>
+BOOST_CXX14_CONSTEXPR T identity_operation ( std::multiplies<T> ) { return T(1); }
+
+template <typename T>
+BOOST_CXX14_CONSTEXPR T identity_operation ( std::plus<T> ) { return T(0); }
+
+
+/// \fn power ( T x, Integer n )
+/// \return the value "x" raised to the power "n"
+/// 
+/// \param x     The value to be exponentiated
+/// \param n     The exponent (must be >= 0)
+///
+//  \remark Taken from Knuth, The Art of Computer Programming, Volume 2:
+//  Seminumerical Algorithms, Section 4.6.3
+template <typename T, typename Integer>
+BOOST_CXX14_CONSTEXPR typename boost::enable_if<boost::is_integral<Integer>, T>::type
+power (T x, Integer n) {
+    T y = 1; // Should be "T y{1};" 
+    if (n == 0) return y;
+    while (true) {
+        if (n % 2 == 1) {
+            y = x * y;
+            if (n == 1)
+                return y;
+            }
+        n = n / 2;
+        x = x * x;
+        }
+    return y;
+    }
+
+/// \fn power ( T x, Integer n, Operation op )
+/// \return the value "x" raised to the power "n"
+/// using the operation "op".
+/// 
+/// \param x     The value to be exponentiated
+/// \param n     The exponent (must be >= 0)
+/// \param op    The operation used
+///
+//  \remark Taken from Knuth, The Art of Computer Programming, Volume 2:
+//  Seminumerical Algorithms, Section 4.6.3
+template <typename T, typename Integer, typename Operation>
+BOOST_CXX14_CONSTEXPR typename boost::enable_if<boost::is_integral<Integer>, T>::type
+power (T x, Integer n, Operation op) {
+    T y = identity_operation(op);
+    if (n == 0) return y;
+    while (true) {
+        if (n % 2 == 1) {
+            y = op(x, y);
+            if (n == 1)
+                return y;
+            }
+        n = n / 2;
+        x = op(x, x);
+        }
+    return y;
+    }
+
+}}
+
+#endif // BOOST_ALGORITHM_HPP