From 261e433a1b11e2af2877d600419bf262f0b5b80a Mon Sep 17 00:00:00 2001
From: jzmaddock <jzmaddock@gmail.com>
Date: Sun, 8 Jun 2014 18:55:11 +0100
Subject: [PATCH] Add scalbn and logb functions, plus float->rational generic
 conversion (base 2 only at present).

---
 .../boost/multiprecision/cpp_dec_float.hpp    | 15 ++++++++
 .../multiprecision/detail/default_ops.hpp     | 23 ++++++++++++
 .../detail/generic_interconvert.hpp           | 37 +++++++++++++++++++
 3 files changed, 75 insertions(+)

diff --git a/include/boost/multiprecision/cpp_dec_float.hpp b/include/boost/multiprecision/cpp_dec_float.hpp
index 7c0dc7aa..e63535b3 100644
--- a/include/boost/multiprecision/cpp_dec_float.hpp
+++ b/include/boost/multiprecision/cpp_dec_float.hpp
@@ -2805,6 +2805,21 @@ inline void eval_trunc(cpp_dec_float<Digits10, ExponentType, Allocator>& result,
    result = x.extract_integer_part();
 }
 
+template <unsigned Digits10, class ExponentType, class Allocator>
+inline void eval_logb(cpp_dec_float<Digits10, ExponentType, Allocator>& result, const cpp_dec_float<Digits10, ExponentType, Allocator>& val)
+{
+   // Set result, to the exponent of val:
+   result = static_cast<long long>(val.order());
+}
+template <unsigned Digits10, class ExponentType, class Allocator, class ArgType>
+inline void eval_scalbn(cpp_dec_float<Digits10, ExponentType, Allocator>& result, const cpp_dec_float<Digits10, ExponentType, Allocator>& val, ArgType e_)
+{
+   using default_ops::eval_multiply;
+   const ExponentType e = e_;
+   cpp_dec_float<Digits10, ExponentType, Allocator> t(1.0, e);
+   eval_multiply(result, val, t);
+}
+
 template <unsigned Digits10, class ExponentType, class Allocator, class ArgType>
 inline void eval_ldexp(cpp_dec_float<Digits10, ExponentType, Allocator>& result, const cpp_dec_float<Digits10, ExponentType, Allocator>& x, ArgType e)
 {
diff --git a/include/boost/multiprecision/detail/default_ops.hpp b/include/boost/multiprecision/detail/default_ops.hpp
index c34177c1..d3bfc082 100644
--- a/include/boost/multiprecision/detail/default_ops.hpp
+++ b/include/boost/multiprecision/detail/default_ops.hpp
@@ -1202,6 +1202,23 @@ template <class T>
 typename enable_if_c<sizeof(T) == 0>::type eval_ldexp();
 template <class T>
 typename enable_if_c<sizeof(T) == 0>::type eval_frexp();
+
+//
+// eval_logb and eval_scalbn simply assume base 2 and forward to
+// eval_ldexp and eval_frexp:
+//
+template <class B>
+inline void eval_logb(B& result, const B& val)
+{
+   typename B::exponent_type e;
+   eval_frexp(result, val, &e);
+   result = static_cast<boost::intmax_t>(e);
+}
+template <class B, class A>
+inline void eval_scalbn(B& result, const B& val, A e)
+{
+   eval_ldexp(result, val, static_cast<typename B::exponent_type>(e));
+}
 //
 // These functions are implemented in separate files, but expanded inline here,
 // DO NOT CHANGE THE ORDER OF THESE INCLUDES:
@@ -2019,6 +2036,12 @@ BINARY_OP_FUNCTOR(pow, number_kind_floating_point)
 BINARY_OP_FUNCTOR(fmod, number_kind_floating_point)
 BINARY_OP_FUNCTOR(atan2, number_kind_floating_point)
 
+UNARY_OP_FUNCTOR(logb, number_kind_floating_point)
+HETERO_BINARY_OP_FUNCTOR(scalbn, short, number_kind_floating_point)
+HETERO_BINARY_OP_FUNCTOR_B(scalbn, int, number_kind_floating_point)
+HETERO_BINARY_OP_FUNCTOR_B(scalbn, long, number_kind_floating_point)
+HETERO_BINARY_OP_FUNCTOR_B(scalbn, long long, number_kind_floating_point)
+
 //
 // Integer functions:
 //
diff --git a/include/boost/multiprecision/detail/generic_interconvert.hpp b/include/boost/multiprecision/detail/generic_interconvert.hpp
index 13659724..ddcbada7 100644
--- a/include/boost/multiprecision/detail/generic_interconvert.hpp
+++ b/include/boost/multiprecision/detail/generic_interconvert.hpp
@@ -222,6 +222,43 @@ void generic_interconvert(To& to, const From& from, const mpl::int_<number_kind_
    eval_divide(to, fn.backend(), fd.backend());
 }
 
+namespace detail{
+
+template <class To, class From>
+void generic_interconvert_float2rational(To& to, const From& from, const mpl::int_<2>& /*radix*/)
+{
+   BOOST_MATH_STD_USING
+   typedef typename mpl::front<typename To::unsigned_types>::type ui_type;
+   static const int shift = std::numeric_limits<long long>::digits;
+   typename From::exponent_type e;
+   typename component_type<To>::type num, denom;
+   number<From> val(from);
+   val = frexp(val, &e);
+   while(val)
+   {
+      val = ldexp(val, shift);
+      e -= shift;
+      long long ll = boost::math::lltrunc(val);
+      val -= ll;
+      num <<= shift;
+      num += ll;
+   }
+   denom = ui_type(1u);
+   if(e < 0)
+      denom <<= -e;
+   else if(e > 0)
+      num <<= e;
+   assign_components(to, num, denom);
+}
+
+}
+
+template <class To, class From>
+void generic_interconvert(To& to, const From& from, const mpl::int_<number_kind_rational>& /*to_type*/, const mpl::int_<number_kind_floating_point>& /*from_type*/)
+{
+   detail::generic_interconvert_float2rational(to, from, mpl::int_<std::numeric_limits<number<From> >::radix>());
+}
+
 }}} // namespaces
 
 #endif  // BOOST_MP_GENERIC_INTERCONVERT_HPP