Review and synchronize Alternate Algos work

include/boost/multiprecision/cpp_df_qf/cpp_df_qf_detail.hpp

@@ -71,63 +71,6 @@ struct exact_arithmetic
    using float_pair  = std::pair<float_type, float_type>;
    using float_tuple = std::tuple<float_type, float_type, float_type, float_type>;
 
-   static
-   #if (defined(_MSC_VER) && (_MSC_VER <= 1900))
-   BOOST_MP_CXX14_CONSTEXPR
-   #else
-   constexpr
-   #endif
-   float_pair split(const float_type& a)
-   {
-      // Split a floating point number in two (high and low) parts approximating the
-      // upper-half and lower-half bits of the float
-
-      static_assert(is_floating_point_or_float128<FloatingPointType>::value,
-                    "Error: exact_arithmetic<>::split invoked with unknown floating-point type");
-
-      // TODO Replace bit shifts with constexpr funcs or ldexp for better compaitibility
-      constexpr int MantissaBits = cpp_df_qf_detail::ccmath::numeric_limits<float_type>::digits;
-      constexpr int SplitBits    = MantissaBits / 2 + 1;
-
-      // Check if the integer is wide enough to hold the Splitter.
-      static_assert(std::numeric_limits<std::uintmax_t>::digits > SplitBits,
-                    "Inadequate integer width for binary shifting needed in split(), try using ldexp instead");
-
-      // If the above line gives an compilation error, replace the
-      // line below it with the commented line
-
-      constexpr float_type Splitter       = FloatingPointType((static_cast<std::uintmax_t>(UINT8_C(1)) << SplitBits) + 1);
-      const     float_type SplitThreshold = (cpp_df_qf_detail::ccmath::numeric_limits<float_type>::max)() / (Splitter * 2);
-
-      float_type hi { };
-      float_type lo { };
-
-      // Handle if multiplication with the splitter would cause overflow
-      if (a > SplitThreshold || a < -SplitThreshold)
-      {
-         constexpr float_type Normalizer = float_type(1ULL << (SplitBits + 1));
-
-         const float_type a_ = a / Normalizer;
-
-         const float_type temp = Splitter * a_;
-
-         hi   = temp - (temp - a_);
-         lo   = a_ - hi;
-
-         hi *= Normalizer;
-         lo *= Normalizer;
-      }
-      else
-      {
-         const float_type temp = Splitter * a;
-
-         hi   = temp - (temp - a);
-         lo   = a - hi;
-      }
-
-      return std::make_pair(hi, lo);
-   }
-
    static
    #if (defined(_MSC_VER) && (_MSC_VER <= 1900))
    BOOST_MP_CXX14_CONSTEXPR
@@ -144,87 +87,6 @@ struct exact_arithmetic
       return result;
    }
 
-   static
-   #if (defined(_MSC_VER) && (_MSC_VER <= 1900))
-   BOOST_MP_CXX14_CONSTEXPR
-   #else
-   constexpr
-   #endif
-   void sum(float_pair& result, float_type a, float_type b)
-   {
-      // Exact addition of two floating point numbers
-      const float_type a_plus_b = a + b;
-      const float_type v        = a_plus_b - a;
-
-      const float_pair tmp(a_plus_b, (a - (a_plus_b - v)) + (b - v));
-
-      result.first  = tmp.first;
-      result.second = tmp.second;
-   }
-
-   #if 0
-   static
-   #if (defined(_MSC_VER) && (_MSC_VER <= 1900))
-   BOOST_MP_CXX14_CONSTEXPR
-   #else
-   constexpr
-   #endif
-   void sum(float_pair& p, float_type& e)
-   {
-      using std::tie;
-
-      float_pair t;
-      float_type t_;
-
-      t                = sum(p.first, p.second);
-      tie(p.first, t_) = sum(e, t.first);
-      tie(p.second, e) = sum(t.second, t_);
-   }
-   #endif
-
-   static
-   #if (defined(_MSC_VER) && (_MSC_VER <= 1900))
-   BOOST_MP_CXX14_CONSTEXPR
-   #else
-   constexpr
-   #endif
-   float_pair difference(const float_type& a, const float_type& b)
-   {
-      // Exact subtraction of two floating point numbers
-      const float_type a_minus_b = a - b;
-      const float_type v         = a_minus_b - a;
-
-      return float_pair(a_minus_b, (a - (a_minus_b - v)) - (b + v));
-   }
-
-   static
-   #if (defined(_MSC_VER) && (_MSC_VER <= 1900))
-   BOOST_MP_CXX14_CONSTEXPR
-   #else
-   constexpr
-   #endif
-   float_pair product(const float_type& a, const float_type& b)
-   {
-      // Exact product of two floating point numbers
-      const float_pair a_split = split(a);
-      const float_pair b_split = split(b);
-
-      const volatile float_type pf = a * b;
-
-      return
-        std::make_pair
-        (
-          const_cast<const float_type&>(pf),
-            (
-                ((a_split.first  * b_split.first) - const_cast<const float_type&>(pf))
-              +  (a_split.first  * b_split.second)
-              +  (a_split.second * b_split.first)
-            )
-          +
-            (a_split.second * b_split.second)
-        );
-   }
-
    static
    #if (defined(_MSC_VER) && (_MSC_VER <= 1900))
    BOOST_MP_CXX14_CONSTEXPR

include/boost/multiprecision/cpp_double_fp.hpp

@@ -246,6 +246,9 @@ class cpp_double_fp_backend
    static constexpr int my_max_exponent10 = static_cast<int>(static_cast<float>(my_max_exponent) * 0.301F);
    static constexpr int my_min_exponent10 = static_cast<int>(static_cast<float>(my_min_exponent) * 0.301F);
 
+   // TBD: Did we justify this static assertion during the GSoC?
+   // Does anyone remember what the meaning of the number 77 is?
+
    static_assert(((my_max_exponent - my_digits) >= 77),
                  "Error: floating-point constituent does not have wide enough exponent range");