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boost/interprocess/detail/math_functions.hpp

```//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Stephen Cleary 2000.
// (C) Copyright Ion Gaztanaga 2007-2011.
//
//    (See accompanying file LICENSE_1_0.txt or copy at
//
// See http://www.boost.org/libs/interprocess for documentation.
//
// This file is a slightly modified file from Boost.Pool
//
//////////////////////////////////////////////////////////////////////////////

#ifndef BOOST_INTERPROCESS_DETAIL_MATH_FUNCTIONS_HPP
#define BOOST_INTERPROCESS_DETAIL_MATH_FUNCTIONS_HPP

#include <climits>
#include <boost/static_assert.hpp>

namespace boost {
namespace interprocess {
namespace ipcdetail {

// 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;
}

//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_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;
}

} // namespace ipcdetail
} // namespace interprocess
} // namespace boost

#endif
```