整理

include/boost/container/detail/math_functions.hpp

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+//////////////////////////////////////////////////////////////////////////////
+//
+// (C) Copyright Stephen Cleary 2000.
+// (C) Copyright Ion Gaztanaga 2007-2013.
+//
+// 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)
+//
+// See http://www.boost.org/libs/container for documentation.
+//
+// This file is a slightly modified file from Boost.Pool
+//
+//////////////////////////////////////////////////////////////////////////////
+
+#ifndef BOOST_CONTAINER_DETAIL_MATH_FUNCTIONS_HPP
+#define BOOST_CONTAINER_DETAIL_MATH_FUNCTIONS_HPP
+
+#ifndef BOOST_CONFIG_HPP
+#  include <boost/config.hpp>
+#endif
+
+#if defined(BOOST_HAS_PRAGMA_ONCE)
+#  pragma once
+#endif
+
+#include <boost/container/detail/config_begin.hpp>
+#include <boost/container/detail/workaround.hpp>
+
+#include <climits>
+
+namespace boost {
+namespace container {
+namespace dtl {
+
+// Greatest common divisor and least common multiple
+
+//
+// gcd is an algorithm that calculates the greatest common divisor of two
+//  integers, using Euclid's algorithm.
+//
+// Pre: A > 0 && B > 0
+// Recommended: A > B
+template <typename Integer>
+inline Integer gcd(Integer A, Integer B)
+{
+   do
+   {
+      const Integer tmp(B);
+      B = A % B;
+      A = tmp;
+   } while (B != 0);
+
+   return A;
+}
+
+//
+// lcm is an algorithm that calculates the least common multiple of two
+//  integers.
+//
+// Pre: A > 0 && B > 0
+// Recommended: A > B
+template <typename Integer>
+inline Integer lcm(const Integer & A, const Integer & B)
+{
+   Integer ret = A;
+   ret /= gcd(A, B);
+   ret *= B;
+   return ret;
+}
+
+template <typename Integer>
+inline Integer log2_ceil(const Integer & A)
+{
+   Integer i = 0;
+   Integer power_of_2 = 1;
+
+   while(power_of_2 < A){
+      power_of_2 <<= 1;
+      ++i;
+   }
+   return i;
+}
+
+template <typename Integer>
+inline Integer upper_power_of_2(const Integer & A)
+{
+   Integer power_of_2 = 1;
+
+   while(power_of_2 < A){
+      power_of_2 <<= 1;
+   }
+   return power_of_2;
+}
+
+template <typename Integer, bool Loop = true>
+struct upper_power_of_2_loop_ct
+{
+
+   template <Integer I, Integer P>
+   struct apply
+   {
+      BOOST_STATIC_CONSTEXPR Integer value =
+         upper_power_of_2_loop_ct<Integer, (I > P*2)>::template apply<I, P*2>::value;
+   };
+};
+
+template <typename Integer>
+struct upper_power_of_2_loop_ct<Integer, false>
+{
+   template <Integer I, Integer P>
+   struct apply
+   {
+      BOOST_STATIC_CONSTEXPR Integer value = P;
+   };
+};
+
+template <typename Integer, Integer I>
+struct upper_power_of_2_ct
+{
+   BOOST_STATIC_CONSTEXPR Integer value = upper_power_of_2_loop_ct<Integer, (I > 1)>::template apply<I, 2>::value;
+};
+
+//This function uses binary search to discover the
+//highest set bit of the integer
+inline std::size_t floor_log2 (std::size_t x)
+{
+   const std::size_t Bits = sizeof(std::size_t)*CHAR_BIT;
+   const bool Size_t_Bits_Power_2= !(Bits & (Bits-1));
+   BOOST_CONTAINER_STATIC_ASSERT(((Size_t_Bits_Power_2)== true));
+
+   std::size_t n = x;
+   std::size_t log2 = 0;
+
+   for(std::size_t shift = Bits >> 1; shift; shift >>= 1){
+      std::size_t tmp = n >> shift;
+      if (tmp)
+         log2 += shift, n = tmp;
+   }
+
+   return log2;
+}
+
+template<std::size_t I1, std::size_t I2>
+struct gcd_ct
+{
+   BOOST_STATIC_CONSTEXPR std::size_t Max = I1 > I2 ? I1 : I2;
+   BOOST_STATIC_CONSTEXPR std::size_t Min = I1 < I2 ? I1 : I2;
+   BOOST_STATIC_CONSTEXPR std::size_t value = gcd_ct<Min, Max % Min>::value;
+};
+
+template<std::size_t I1>
+struct gcd_ct<I1, 0>
+{
+   BOOST_STATIC_CONSTEXPR std::size_t value = I1;
+};
+
+template<std::size_t I1>
+struct gcd_ct<0, I1>
+{
+   BOOST_STATIC_CONSTEXPR std::size_t value = I1;
+};
+
+template<std::size_t I1, std::size_t I2>
+struct lcm_ct
+{
+   BOOST_STATIC_CONSTEXPR std::size_t value = I1 * I2 / gcd_ct<I1, I2>::value;
+};
+
+} // namespace dtl
+} // namespace container
+} // namespace boost
+
+#include <boost/container/detail/config_end.hpp>
+
+#endif