double quwl ( double rad )
{
	auto double xN = 1 , xNplus1 = 1 / ( 2 * xN ) * ( xN * xN + rad ) ;
 
	auto unsigned char i ;
 
	while ( xN != xNplus1 )
	{
		xN = xNplus1 ;
		xNplus1 = 1 / ( 2 * xN ) * ( xN * xN + rad ) ;
	}
 
	return xNplus1 ;
}

double quwl ( double rad )
{
	if ( rad < 0 ) return - 1 ;
 
	auto double xN = 1 ;
 
	if ( xN  < sqrt ( DBL_MIN )                 ||
		 xN  > sqrt ( DBL_MAX )                 ||
		 rad > DBL_MAX - xN * xN ) return - 1 ;
 
	auto double xNplus1 = 1 / ( 2 * xN ) * ( xN * xN + rad ) ;
 
	while ( fabs ( xNplus1 - xN ) > rad * 1e-14                       &&
						  xNplus1 > sqrt ( DBL_MIN ) - 1              &&
						  xNplus1 < sqrt ( DBL_MAX ) + 1              &&
			    			  rad < DBL_MAX - xNplus1 * xNplus1 + 1 )
	{
		xN = xNplus1 ;
 
		xNplus1 = 1 / ( 2 * xN ) * ( xN * xN + rad ) ;
	}
 
	return xNplus1 ;
}