From 7f1a45870a2072e4575615959cd2ede218124ce2 Mon Sep 17 00:00:00 2001
From: John Maddock <john@johnmaddock.co.uk>
Date: Thu, 21 Apr 2011 18:11:37 +0000
Subject: [PATCH] Change fp_traits to handle sign manipulation separately from
 fp-classification. Fixes some Linux/GCC regressions but not yet all.

[SVN r71405]
---
 .../special_functions/detail/fp_traits.hpp    |  3 +-
 include/boost/math/special_functions/sign.hpp | 30 +++++++------------
 2 files changed, 13 insertions(+), 20 deletions(-)

diff --git a/include/boost/math/special_functions/detail/fp_traits.hpp b/include/boost/math/special_functions/detail/fp_traits.hpp
index 0f311b639..54d45917b 100644
--- a/include/boost/math/special_functions/detail/fp_traits.hpp
+++ b/include/boost/math/special_functions/detail/fp_traits.hpp
@@ -552,12 +552,13 @@ struct select_native<long double>
 
 template<class T> struct fp_traits
 {
+    typedef BOOST_DEDUCED_TYPENAME size_to_precision<sizeof(T), ::boost::is_floating_point<T>::value>::type precision;
 #if defined(BOOST_MATH_USE_STD_FPCLASSIFY) && !defined(BOOST_MATH_DISABLE_STD_FPCLASSIFY)
     typedef typename select_native<T>::type type;
 #else
-    typedef BOOST_DEDUCED_TYPENAME size_to_precision<sizeof(T), ::boost::is_floating_point<T>::value>::type precision;
     typedef fp_traits_non_native<T, precision> type;
 #endif
+    typedef fp_traits_non_native<T, precision> sign_change_type;
 };
 
 //------------------------------------------------------------------------------
diff --git a/include/boost/math/special_functions/sign.hpp b/include/boost/math/special_functions/sign.hpp
index 405bfc021..3163fc23e 100644
--- a/include/boost/math/special_functions/sign.hpp
+++ b/include/boost/math/special_functions/sign.hpp
@@ -66,14 +66,6 @@ namespace detail {
 
     // Changesign
 
-#ifdef BOOST_MATH_USE_STD_FPCLASSIFY
-    template<class T> 
-    inline int changesign_impl(T x, native_tag const&)
-    {
-         return -x;
-    }
-#endif
-
     template<class T>
     inline T (changesign_impl)(T x, generic_tag<true> const&)
     {
@@ -90,7 +82,7 @@ namespace detail {
     template<class T>
     inline T changesign_impl(T x, ieee_copy_all_bits_tag const&)
     {
-        typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::type traits;
+        typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::sign_change_type traits;
 
         BOOST_DEDUCED_TYPENAME traits::bits a;
         traits::get_bits(x,a);
@@ -102,7 +94,7 @@ namespace detail {
     template<class T>
     inline T (changesign_impl)(T x, ieee_copy_leading_bits_tag const&)
     {
-        typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::type traits;
+        typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::sign_change_type traits;
 
         BOOST_DEDUCED_TYPENAME traits::bits a;
         traits::get_bits(x,a);
@@ -115,7 +107,7 @@ namespace detail {
 }   // namespace detail
 
 template<class T> int (signbit)(T x)
-{ //!< \brief return true if floating-point type T is NaN (Not A Number).
+{ 
    typedef typename detail::fp_traits<T>::type traits;
    typedef typename traits::method method;
    typedef typename boost::is_floating_point<T>::type fp_tag;
@@ -128,22 +120,22 @@ inline int sign BOOST_NO_MACRO_EXPAND(const T& z)
    return (z == 0) ? 0 : (boost::math::signbit)(z) ? -1 : 1;
 }
 
-template <class T>
-inline T copysign BOOST_NO_MACRO_EXPAND(const T& x, const T& y)
-{
-   BOOST_MATH_STD_USING
-      return fabs(x) * ((boost::math::signbit)(y) ? -1 : 1);
-}
-
 template<class T> T (changesign)(T x)
 { //!< \brief return unchanged binary pattern of x, except for change of sign bit. 
-   typedef typename detail::fp_traits<T>::type traits;
+   typedef typename detail::fp_traits<T>::sign_change_type traits;
    typedef typename traits::method method;
    typedef typename boost::is_floating_point<T>::type fp_tag;
 
    return detail::changesign_impl(x, method());
 }
 
+template <class T>
+inline T copysign BOOST_NO_MACRO_EXPAND(const T& x, const T& y)
+{
+   BOOST_MATH_STD_USING
+   return (boost::math::signbit)(x) != (boost::math::signbit)(y) ? (boost::math::changesign)(x) : x;
+}
+
 } // namespace math
 } // namespace boost