From 8043bafb6b02bb705961e6c3973746050a81c04a Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Tue, 14 Sep 2021 16:50:34 +0300
Subject: [PATCH] Add a generic cmath.hpp implementation, enabled when
 BOOST_CORE_USE_GENERIC_CMATH is defined

---
 include/boost/core/cmath.hpp | 99 ++++++++++++++++++++++++++++++++++++
 test/Jamfile.v2              |  1 +
 2 files changed, 100 insertions(+)

diff --git a/include/boost/core/cmath.hpp b/include/boost/core/cmath.hpp
index 0e5fa1f..266e2f7 100644
--- a/include/boost/core/cmath.hpp
+++ b/include/boost/core/cmath.hpp
@@ -17,6 +17,103 @@
 // https://www.boost.org/LICENSE_1_0.txt
 
 #include <cmath>
+
+#if defined(BOOST_CORE_USE_GENERIC_CMATH)
+
+#include <boost/cstdint.hpp>
+#include <boost/static_assert.hpp>
+#include <limits>
+#include <cstring>
+
+namespace boost
+{
+namespace core
+{
+
+// fpclassify return values
+
+int const fp_zero = 0;
+int const fp_subnormal = 1;
+int const fp_normal = 2;
+int const fp_infinite = 3;
+int const fp_nan = 4;
+
+// Classification functions
+
+template<class T> bool isfinite( T x )
+{
+    return x <= (std::numeric_limits<T>::max)() && x >= -(std::numeric_limits<T>::max)();
+}
+
+template<class T> bool isinf( T x )
+{
+    return x > (std::numeric_limits<T>::max)() || x < -(std::numeric_limits<T>::max)();
+}
+
+template<class T> bool isnan( T x )
+{
+    return !isfinite( x ) && !isinf( x );
+}
+
+template<class T> bool isnormal( T x )
+{
+    return isfinite( x ) && ( x >= (std::numeric_limits<T>::min)() || x <= -(std::numeric_limits<T>::min)() );
+}
+
+template<class T> int fpclassify( T x )
+{
+    if( x == 0 ) return fp_zero;
+
+    if( x < 0 ) x = -x;
+
+    if( x > (std::numeric_limits<T>::max)() ) return fp_infinite;
+
+    if( x >= (std::numeric_limits<T>::min)() ) return fp_normal;
+
+    if( x < (std::numeric_limits<T>::min)() ) return fp_subnormal;
+
+    return fp_nan;
+}
+
+// Sign manipulation functions
+
+inline bool signbit( float x )
+{
+    boost::int32_t y;
+
+    BOOST_STATIC_ASSERT( sizeof( x ) == sizeof( y ) );
+
+    std::memcpy( &y, &x, sizeof( y ) );
+
+    return y < 0;
+}
+
+inline bool signbit( double x )
+{
+    boost::int64_t y;
+
+    BOOST_STATIC_ASSERT( sizeof( x ) == sizeof( y ) );
+
+    std::memcpy( &y, &x, sizeof( y ) );
+
+    return y < 0;
+}
+
+inline bool signbit( long double x )
+{
+    return signbit( static_cast<double>( x ) );
+}
+
+template<class T> T copysign( T x, T y )
+{
+    return signbit( x ) == signbit( y )? x: -x;
+}
+
+} // namespace core
+} // namespace boost
+
+#else // defined(BOOST_CORE_USE_GENERIC_CMATH)
+
 #if defined(_MSC_VER) && _MSC_VER < 1800
 # include <float.h>
 #endif
@@ -196,4 +293,6 @@ template<class T> T copysign( T x, T y )
 } // namespace core
 } // namespace boost
 
+#endif // defined(BOOST_CORE_USE_GENERIC_CMATH)
+
 #endif  // #ifndef BOOST_CORE_CMATH_HPP_INCLUDED
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index c285885..867c99c 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -232,6 +232,7 @@ run no_exceptions_support_test.cpp ;
 run no_exceptions_support_test.cpp : : : <exception-handling>off : no_exceptions_support_test_nx ;
 
 run cmath_test.cpp ;
+run cmath_test.cpp : : : <define>BOOST_CORE_USE_GENERIC_CMATH : cmath_test_generic ;
 
 run bit_cast_test.cpp ;
 run bit_rotate_test.cpp ;