floating point comparsion

https://github.com/acfr/comma/blob/master/math/compare.h

template < typename S > inline bool equal( float lhs, S rhs ) { return std::fabs( lhs - rhs ) < std::numeric_limits< float >::epsilon(); }

template < typename S > inline bool less( float lhs, S rhs ) { return static_cast< float >( rhs ) - lhs >= std::numeric_limits< float >::epsilon(); }

template < typename S > inline bool equal( double lhs, S rhs ) { return std::fabs( lhs - rhs ) < std::numeric_limits< double >::epsilon(); }

template < typename S > inline bool less( double lhs, S rhs ) { return static_cast< double >( rhs ) - lhs >= std::numeric_limits< double >::epsilon(); }

template < typename S > inline bool equal( long double lhs, S rhs ) { return std::fabs( lhs - rhs ) < std::numeric_limits< long double >::epsilon(); }

template < typename S > inline bool less( long double lhs, S rhs ) { return static_cast< long double >( rhs ) - lhs >= std::numeric_limits< long double >::epsilon(); }

template < typename T, typename S > inline bool equal( const T& lhs, const S& rhs ) { return lhs == rhs; }

template < typename T, typename S > inline bool less( const T& lhs, const S& rhs ) { return lhs < rhs; }

template < typename T, typename S, typename Diff > inline bool less( const T& lhs, const S& rhs, const Diff& epsilon ) { return less( lhs + epsilon, rhs ); }

template < typename T, typename S, typename Diff > inline bool equal( const T& lhs, const S& rhs, const Diff& epsilon ) { return !less( lhs, rhs, epsilon ) && !less( static_cast< T >( rhs ), lhs, epsilon );