utility.hpp

来自「矩阵运算源码最新版本」· HPP 代码 · 共 64 行

// Software License for MTL
// 
// Copyright (c) 2007 The Trustees of Indiana University. All rights reserved.
// Authors: Peter Gottschling and Andrew Lumsdaine
// 
// This file is part of the Matrix Template Library
// 
// See also license.mtl.txt in the distribution.

#ifndef MTL_RECURSION_UTILITIES_INCLUDE
#define MTL_RECURSION_UTILITIES_INCLUDE

#include <limits>
#include <cmath>

namespace mtl { namespace recursion {


// Splits a number into a next-smallest power of 2 and rest
std::size_t inline first_part(std::size_t n)
{
    if (n == 0) return 0;

    std::size_t i= std::numeric_limits<std::size_t>::max()/2 + 1;

    while(i >= n) i>>= 1;
    return i;
}


// The remainder of first part
std::size_t inline second_part(std::size_t n)
{
    return n - first_part(n);
}


template <typename Matrix>
std::size_t inline outer_bound(Matrix const& matrix)
{
  std::size_t max_dim=std::max(matrix.num_rows(), matrix.num_cols()), bound= 1;
  for (; bound < max_dim;) bound<<= 1;
  return bound;
}


template <typename Integral>
Integral inline least_significant_one_bit(Integral x)
{
  return ((x ^ x-1) + 1) >> 1;
}


template <typename Integral>
bool inline is_power_of_2(Integral x)
{
  return x == least_significant_one_bit(x);
}


}} // namespace mtl::recursion

#endif // MTL_RECURSION_UTILITIES_INCLUDE