ObjexxFCL::bit bit_ashift tweak to avoid left shift of negative values

third_party/ObjexxFCL/src/ObjexxFCL/bit.hh

@@ -291,12 +291,12 @@ bit_cshift( T const & x, S const & shift ) // x<0 behavior varies in Fortran ISH
 }
 
 // Bit Arithmetic Shifted
-template< typename T, typename S >
+template< typename T, typename S, class = typename std::enable_if< std::is_unsigned< T >::value >::type >
 inline
 T
 bit_ashift( T const & x, S const & shift )
 {
-	static auto const x_bits( bit_size( x ) );
+	auto const x_bits( std::numeric_limits< T >::digits );
 	if ( shift >= S( 0 ) ) {
 		return ( shift < x_bits ? x << shift : T( 0 ) );
 	} else { // Negative (right) shift
@@ -308,6 +308,24 @@ bit_ashift( T const & x, S const & shift )
 	}
 }
 
+// Bit Arithmetic Shifted
+template< typename T, typename S, class = typename std::enable_if< std::is_signed< T >::value >::type, typename = void >
+inline
+T
+bit_ashift( T const & x, S const & shift )
+{
+	auto const x_bits( std::numeric_limits< T >::digits + 1 );
+	if ( shift >= S( 0 ) ) {
+		return ( shift < x_bits ? *reinterpret_cast< typename std::make_unsigned< T const >::type * >( &x ) << shift : T( 0 ) );
+	} else { // Negative (right) shift
+		if ( x >= T( 0 ) ) {
+			return ( -shift < x_bits ? x >> -shift : T( 0 ) );
+		} else {
+			return ( -shift < x_bits ? x >> -shift | ~( ( S( 1 ) << ( x_bits + shift ) ) - 1 ) : T( 0 ) );
+		}
+	}
+}
+
 // Bit Right Arithmetic Shifted
 template< typename T, typename S >
 inline