diff --git a/sprout/config/auto_config.hpp b/sprout/config/auto_config.hpp
index 54ad7f29..e80c9e4e 100644
--- a/sprout/config/auto_config.hpp
+++ b/sprout/config/auto_config.hpp
@@ -123,6 +123,15 @@
 #	endif	// #ifdef SPROUT_HAS_CONSTEXPR_CMATH_FUNCTION
 #endif	// #ifndef SPROUT_CONFIG_DISABLE_BUILTIN_CMATH_FUNCTION
 
+//
+// SPROUT_CONFIG_DISABLE_BUILTIN_COPYSIGN_FUNCTION
+//
+#ifndef SPROUT_CONFIG_DISABLE_BUILTIN_COPYSIGN_FUNCTION
+#	ifndef SPROUT_HAS_CONSTEXPR_COPYSIGN_FUNCTION
+#		define SPROUT_CONFIG_DISABLE_BUILTIN_COPYSIGN_FUNCTION
+#	endif	// #ifdef SPROUT_HAS_CONSTEXPR_COPYSIGN_FUNCTION
+#endif	// #ifndef SPROUT_CONFIG_DISABLE_BUILTIN_COPYSIGN_FUNCTION
+
 //
 // SPROUT_CONFIG_DISABLE_BUILTIN_BIT_OPERATION
 //
diff --git a/sprout/config/compiler/clang.hpp b/sprout/config/compiler/clang.hpp
index 8e84cde3..0754f2ff 100644
--- a/sprout/config/compiler/clang.hpp
+++ b/sprout/config/compiler/clang.hpp
@@ -56,6 +56,10 @@
 #	define SPROUT_NO_CXX14_VARIABLE_TEMPLATES
 #endif
 
+#if (__clang_major__ > 3 || (__clang_major__ == 3 && __clang_minor__ >= 0))
+#	define SPROUT_HAS_CONSTEXPR_COPYSIGN_FUNCTION
+#endif
+
 #if !defined(SPROUT_NO_CXX11_CONSTEXPR)
 #	define SPROUT_WORKAROUND_NOT_TERMINATE_RECURSIVE_CONSTEXPR_FUNCTION_TEMPLATE
 #endif
diff --git a/sprout/config/compiler/gcc.hpp b/sprout/config/compiler/gcc.hpp
index 6399a932..501d9874 100644
--- a/sprout/config/compiler/gcc.hpp
+++ b/sprout/config/compiler/gcc.hpp
@@ -52,6 +52,10 @@
 #	define SPROUT_HAS_CONSTEXPR_CMATH_FUNCTION
 #endif
 
+#if ((__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)) && defined(__GXX_EXPERIMENTAL_CXX0X__))
+#	define SPROUT_HAS_CONSTEXPR_COPYSIGN_FUNCTION
+#endif
+
 #if ((__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)) && defined(__GXX_EXPERIMENTAL_CXX0X__))
 #	define SPROUT_HAS_CONSTEXPR_BIT_OPERATION
 #endif
diff --git a/sprout/config/suffix.hpp b/sprout/config/suffix.hpp
index 630e5779..354e2814 100644
--- a/sprout/config/suffix.hpp
+++ b/sprout/config/suffix.hpp
@@ -167,6 +167,15 @@
 #	define SPROUT_USE_BUILTIN_CMATH_FUNCTION 0
 #endif	// #ifndef SPROUT_CONFIG_DISABLE_BUILTIN_CMATH_FUNCTION
 
+//
+// SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION
+//
+#ifndef SPROUT_CONFIG_DISABLE_BUILTIN_COPYSIGN_FUNCTION
+#	define SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION 1
+#else	// #ifndef SPROUT_CONFIG_DISABLE_BUILTIN_COPYSIGN_FUNCTION
+#	define SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION 0
+#endif	// #ifndef SPROUT_CONFIG_DISABLE_BUILTIN_COPYSIGN_FUNCTION
+
 //
 // SPROUT_USE_BUILTIN_BIT_OPERATION
 //
diff --git a/sprout/math/atan2.hpp b/sprout/math/atan2.hpp
index 1ead7f61..63973bf5 100644
--- a/sprout/math/atan2.hpp
+++ b/sprout/math/atan2.hpp
@@ -55,7 +55,7 @@ namespace sprout {
 		// atan2
 		//
 		// issue:
-		//	[ !SPROUT_USE_BUILTIN_CMATH_FUNCTION ]
+		//	[ !(SPROUT_USE_BUILTIN_CMATH_FUNCTION || SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION) ]
 		//	atan2(�}0, -0) returns �}�� .
 		//		# returns �}0 . ( same as atan2(�}0, +0) )
 		//	atan2(-0, x) returns -�� for x < 0.
diff --git a/sprout/math/copysign.hpp b/sprout/math/copysign.hpp
index e1fd8fe9..9ce73ecf 100644
--- a/sprout/math/copysign.hpp
+++ b/sprout/math/copysign.hpp
@@ -13,14 +13,13 @@
 #include <sprout/limits.hpp>
 #include <sprout/math/detail/config.hpp>
 #include <sprout/math/isnan.hpp>
-#include <sprout/math/signbit.hpp>
 #include <sprout/type_traits/float_promote.hpp>
 #include <sprout/type_traits/enabler_if.hpp>
 
 namespace sprout {
 	namespace math {
 		namespace detail {
-#if SPROUT_USE_BUILTIN_CMATH_FUNCTION
+#if SPROUT_USE_BUILTIN_CMATH_FUNCTION || SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION
 			inline SPROUT_CONSTEXPR float
 			builtin_copysign(float x, float y) {
 				return __builtin_copysignf(x, y);
@@ -34,12 +33,17 @@ namespace sprout {
 				return __builtin_copysignl(x, y);
 			}
 #endif
+			template<typename FloatType>
+			inline SPROUT_CONSTEXPR bool
+			broken_signbit(FloatType x) {
+				return !sprout::math::isnan(x) && x < 0;
+			}
 		}	// namespace detail
 		//
 		// copysign
 		//
 		// issue:
-		//	[ !SPROUT_USE_BUILTIN_CMATH_FUNCTION ]
+		//	[ !(SPROUT_USE_BUILTIN_CMATH_FUNCTION || SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION) ]
 		//	copysign(�}x, -0) returns -x for |x| is not 0 .
 		//		# returns +x . ( same as copysign(�}x, +0) )
 		//	copysign(�}x, -NaN) returns -x for |x| is not NaN .
@@ -52,18 +56,18 @@ namespace sprout {
 		inline SPROUT_CONSTEXPR FloatType
 		copysign(FloatType x, FloatType y) {
 			return
-#if SPROUT_USE_BUILTIN_CMATH_FUNCTION
+#if SPROUT_USE_BUILTIN_CMATH_FUNCTION || SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION
 				sprout::math::detail::builtin_copysign(x, y)
 #else
 				x == 0
 					? y == 0 ? y
-						: sprout::math::signbit(y) ? -FloatType(0)
+						: sprout::math::detail::broken_signbit(y) ? -FloatType(0)
 						: FloatType(0)
 				: sprout::math::isnan(x)
 					? sprout::math::isnan(y) ? y
-						: sprout::math::signbit(y) ? -sprout::numeric_limits<FloatType>::quiet_NaN()
+						: sprout::math::detail::broken_signbit(y) ? -sprout::numeric_limits<FloatType>::quiet_NaN()
 						: sprout::numeric_limits<FloatType>::quiet_NaN()
-				: sprout::math::signbit(y) != sprout::math::signbit(x) ? -x
+				: sprout::math::detail::broken_signbit(y) != sprout::math::detail::broken_signbit(x) ? -x
 				: x
 #endif
 				;
diff --git a/sprout/math/pow.hpp b/sprout/math/pow.hpp
index 811e66c2..6b6923ea 100644
--- a/sprout/math/pow.hpp
+++ b/sprout/math/pow.hpp
@@ -51,7 +51,7 @@ namespace sprout {
 		// pow
 		//
 		// issue:
-		//	[ !SPROUT_USE_BUILTIN_CMATH_FUNCTION ]
+		//	[ !(SPROUT_USE_BUILTIN_CMATH_FUNCTION || SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION) ]
 		//	pow(-0, y) returns -�� for y an odd integer < 0.
 		//		# returns +�� . ( same as pow(+0, y) )
 		//
diff --git a/sprout/math/signbit.hpp b/sprout/math/signbit.hpp
index 7b0a3a17..3c49a8ad 100644
--- a/sprout/math/signbit.hpp
+++ b/sprout/math/signbit.hpp
@@ -11,7 +11,7 @@
 #include <type_traits>
 #include <sprout/config.hpp>
 #include <sprout/math/detail/config.hpp>
-#include <sprout/math/isnan.hpp>
+#include <sprout/math/copysign.hpp>
 #include <sprout/type_traits/enabler_if.hpp>
 
 namespace sprout {
@@ -29,7 +29,7 @@ namespace sprout {
 		// signbit
 		//
 		// issue:
-		//	[ !SPROUT_USE_BUILTIN_CMATH_FUNCTION ]
+		//	[ !(SPROUT_USE_BUILTIN_CMATH_FUNCTION || SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION) ]
 		//	signbit(-0) returns false .
 		//		# returns true . ( same as signbit(+0) )
 		//	signbit(-NaN) returns false .
@@ -44,8 +44,10 @@ namespace sprout {
 			return
 #if SPROUT_USE_BUILTIN_CMATH_FUNCTION
 				sprout::math::detail::builtin_signbit(x)
+#elif SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION
+				sprout::math::copysign(FloatType(1), x) < FloatType(0)
 #else
-				!sprout::math::isnan(x) && x < 0
+				sprout::math::detail::broken_signbit(x)
 #endif
 				;
 		}
diff --git a/sprout/math/tgamma.hpp b/sprout/math/tgamma.hpp
index 94c70d98..6932efa9 100644
--- a/sprout/math/tgamma.hpp
+++ b/sprout/math/tgamma.hpp
@@ -127,7 +127,7 @@ namespace sprout {
 		// tgamma
 		//
 		// issue:
-		//	[ !SPROUT_USE_BUILTIN_CMATH_FUNCTION ]
+		//	[ !(SPROUT_USE_BUILTIN_CMATH_FUNCTION || SPROUT_USE_BUILTIN_COPYSIGN_FUNCTION) ]
 		//	tgamma(-0) returns -�� .
 		//		# returns +�� . ( same as tgamma(+0) )
 		//