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119 lines
2.6 KiB
C++
119 lines
2.6 KiB
C++
//////////////////////////////////////////////////////////////////////////////
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//
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// (C) Copyright Stephen Cleary 2000.
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// (C) Copyright Ion Gaztanaga 2007-2012.
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//
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// See http://www.boost.org/libs/interprocess for documentation.
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//
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// This file is a slightly modified file from Boost.Pool
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//
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//////////////////////////////////////////////////////////////////////////////
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#ifndef BOOST_INTERPROCESS_DETAIL_MATH_FUNCTIONS_HPP
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#define BOOST_INTERPROCESS_DETAIL_MATH_FUNCTIONS_HPP
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#ifndef BOOST_CONFIG_HPP
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# include <boost/config.hpp>
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#endif
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#
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#if defined(BOOST_HAS_PRAGMA_ONCE)
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# pragma once
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#endif
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#include <climits>
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#include <boost/static_assert.hpp>
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namespace boost {
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namespace interprocess {
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namespace ipcdetail {
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// Greatest common divisor and least common multiple
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//
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// gcd is an algorithm that calculates the greatest common divisor of two
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// integers, using Euclid's algorithm.
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//
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// Pre: A > 0 && B > 0
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// Recommended: A > B
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template <typename Integer>
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inline Integer gcd(Integer A, Integer B)
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{
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do
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{
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const Integer tmp(B);
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B = A % B;
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A = tmp;
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} while (B != 0);
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return A;
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}
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//
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// lcm is an algorithm that calculates the least common multiple of two
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// integers.
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//
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// Pre: A > 0 && B > 0
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// Recommended: A > B
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template <typename Integer>
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inline Integer lcm(const Integer & A, const Integer & B)
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{
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Integer ret = A;
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ret /= gcd(A, B);
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ret *= B;
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return ret;
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}
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template <typename Integer>
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inline Integer log2_ceil(const Integer & A)
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{
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Integer i = 0;
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Integer power_of_2 = 1;
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while(power_of_2 < A){
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power_of_2 <<= 1;
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++i;
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}
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return i;
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}
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template <typename Integer>
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inline Integer upper_power_of_2(const Integer & A)
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{
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Integer power_of_2 = 1;
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while(power_of_2 < A){
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power_of_2 <<= 1;
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}
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return power_of_2;
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}
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//This function uses binary search to discover the
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//highest set bit of the integer
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inline std::size_t floor_log2 (std::size_t x)
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{
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const std::size_t Bits = sizeof(std::size_t)*CHAR_BIT;
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const bool Size_t_Bits_Power_2= !(Bits & (Bits-1));
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BOOST_STATIC_ASSERT(((Size_t_Bits_Power_2)== true));
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std::size_t n = x;
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std::size_t log2 = 0;
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for(std::size_t shift = Bits >> 1; shift; shift >>= 1){
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std::size_t tmp = n >> shift;
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if (tmp)
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log2 += shift, n = tmp;
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}
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return log2;
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}
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} // namespace ipcdetail
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} // namespace interprocess
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} // namespace boost
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#endif
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