From 7ea0caa72c2a9ee1264cac049541154efe939ea0 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Mon, 23 Nov 2020 05:20:28 +0200
Subject: [PATCH] Use std:: <cmath> functions, except on msvc-11.0 and below

---
 include/boost/lexical_cast/detail/inf_nan.hpp | 56 ++++++++++---------
 1 file changed, 31 insertions(+), 25 deletions(-)

diff --git a/include/boost/lexical_cast/detail/inf_nan.hpp b/include/boost/lexical_cast/detail/inf_nan.hpp
index 72a2ae9..5db7182 100644
--- a/include/boost/lexical_cast/detail/inf_nan.hpp
+++ b/include/boost/lexical_cast/detail/inf_nan.hpp
@@ -32,7 +32,6 @@
 #include <cstddef>
 #include <cstring>
 #include <cmath>
-#include <math.h>
 #if defined(_MSC_VER) && _MSC_VER < 1800
 # include <float.h>
 #endif
@@ -51,29 +50,39 @@ namespace boost {
             return true;
         }
 
+        namespace lcast_math
+        {
 #if defined(_MSC_VER) && _MSC_VER < 1800
 
-        template<class T> T copysign( T x, T y )
-        {
-            return static_cast<T>( _copysign( static_cast<double>( x ), static_cast<double>( y ) ) );
-        }
+            template<class T> T copysign( T x, T y )
+            {
+                return static_cast<T>( _copysign( static_cast<double>( x ), static_cast<double>( y ) ) );
+            }
 
-        template<class T> bool isnan( T x )
-        {
-            return _isnan( static_cast<double>( x ) ) != 0;
-        }
+            template<class T> bool isnan( T x )
+            {
+                return _isnan( static_cast<double>( x ) ) != 0;
+            }
 
-        template<class T> bool isinf( T x )
-        {
-            return ( _fpclass( static_cast<double>( x ) ) & ( _FPCLASS_PINF | _FPCLASS_NINF ) ) != 0;
-        }
+            template<class T> bool isinf( T x )
+            {
+                return ( _fpclass( static_cast<double>( x ) ) & ( _FPCLASS_PINF | _FPCLASS_NINF ) ) != 0;
+            }
 
-        template<class T> bool signbit( T x )
-        {
-            return _copysign( 1.0, static_cast<double>( x ) ) < 0.0;
-        }
+            template<class T> bool signbit( T x )
+            {
+                return _copysign( 1.0, static_cast<double>( x ) ) < 0.0;
+            }
+
+#else
+
+            using ::copysign; // it is what it is
+            using std::isnan;
+            using std::isinf;
+            using std::signbit;
 
 #endif
+        } // namespace lcast_math
 
         /* Returns true and sets the correct value if found NaN or Inf. */
         template <class CharT, class T>
@@ -105,7 +114,7 @@ namespace boost {
                 }
 
                 if( !has_minus ) value = std::numeric_limits<T>::quiet_NaN();
-                else value = copysign(std::numeric_limits<T>::quiet_NaN(), static_cast<T>(-1));
+                else value = lcast_math::copysign(std::numeric_limits<T>::quiet_NaN(), static_cast<T>(-1));
                 return true;
             } else if (
                 ( /* 'INF' or 'inf' */
@@ -132,12 +141,9 @@ namespace boost {
                          , const CharT* lc_nan
                          , const CharT* lc_infinity) BOOST_NOEXCEPT
         {
-#if defined(__GNUC__)
-            using std::signbit;
-#endif
             const CharT minus = lcast_char_constants<CharT>::minus;
-            if (isnan(value)) {
-                if (signbit(value)) {
+            if (lcast_math::isnan(value)) {
+                if (lcast_math::signbit(value)) {
                     *begin = minus;
                     ++ begin;
                 }
@@ -145,8 +151,8 @@ namespace boost {
                 std::memcpy(begin, lc_nan, 3 * sizeof(CharT));
                 end = begin + 3;
                 return true;
-            } else if (isinf(value)) {
-                if (signbit(value)) {
+            } else if (lcast_math::isinf(value)) {
+                if (lcast_math::signbit(value)) {
                     *begin = minus;
                     ++ begin;
                 }