ceph/src/boost/boost/multiprecision/traits/max_digits10.hpp

   1 ///////////////////////////////////////////////////////////////
   2 //  Copyright 2012 John Maddock. Distributed under the Boost
   3 //  Software License, Version 1.0. (See accompanying file
   4 //  LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt
   5
   6 #ifndef BOOST_MATH_MAX_DIGITS10_HPP
   7 #define BOOST_MATH_MAX_DIGITS10_HPP
   8
   9 namespace boost {
  10 namespace multiprecision {
  11 namespace detail {
  12
  13 template <unsigned digits>
  14 struct calc_max_digits10
  15 {
  16    static constexpr unsigned max_digits_10(unsigned d)
  17    {
  18       //
  19       // We need ceil(log10(2) * d) + 1 decimal places to
  20       // guarantee round tripping, see: https://www.exploringbinary.com/number-of-digits-required-for-round-trip-conversions/
  21       // and references therein.  Since log10(2) is irrational, then d*log10(2) will
  22       // never be exactly an integer so we can replace by trunc(log10(2) * d) + 2
  23       // and avoid the call to ceil:
  24       //
  25       return static_cast<unsigned>(0.301029995663981195213738894724493026768189881462108541310 * d) + 2;
  26    }
  27    static constexpr const unsigned value = max_digits_10(digits);
  28 };
  29
  30 template <std::size_t digits>
  31 struct calc_max_digits10_s
  32 {
  33    static constexpr std::size_t max_digits_10(std::size_t d)
  34    {
  35       //
  36       // We need ceil(log10(2) * d) + 1 decimal places to
  37       // guarantee round tripping, see: https://www.exploringbinary.com/number-of-digits-required-for-round-trip-conversions/
  38       // and references therein.  Since log10(2) is irrational, then d*log10(2) will
  39       // never be exactly an integer so we can replace by trunc(log10(2) * d) + 2
  40       // and avoid the call to ceil:
  41       //
  42       return static_cast<std::size_t>(0.301029995663981195213738894724493026768189881462108541310 * d) + 2;
  43    }
  44    static constexpr const std::size_t value = max_digits_10(digits);
  45 };
  46
  47 template <unsigned digits>
  48 struct calc_digits10
  49 {
  50    static constexpr unsigned digits_10(unsigned d)
  51    {
  52       //
  53       // We need floor(log10(2) * (d-1)), see:
  54       // https://www.exploringbinary.com/number-of-digits-required-for-round-trip-conversions/
  55       // and references therein.
  56       //
  57       return static_cast<unsigned>(0.301029995663981195213738894724493026768189881462108541310 * (d - 1));
  58    }
  59    static constexpr const unsigned value = digits_10(digits);
  60 };
  61
  62 template <std::size_t digits>
  63 struct calc_digits10_s
  64 {
  65    static constexpr std::size_t digits_10(std::size_t d)
  66    {
  67       //
  68       // We need floor(log10(2) * (d-1)), see:
  69       // https://www.exploringbinary.com/number-of-digits-required-for-round-trip-conversions/
  70       // and references therein.
  71       //
  72       return static_cast<std::size_t>(0.301029995663981195213738894724493026768189881462108541310 * (d - 1));
  73    }
  74    static constexpr const std::size_t value = digits_10(digits);
  75 };
  76
  77 }}} // namespace boost::multiprecision::detail
  78
  79 #endif