function deg2radf( x ) {
	return float64ToFloat32( float64ToFloat32( x ) * PI_DIV_180 );
}
Converts an angle from degrees to radians (single-precision).

@param {number} x - angle in degrees
@returns {number} angle in radians

@example
var r = deg2radf( 90.0 );
// returns ~1.571

@example
var r = deg2radf( -45.0 );
// returns ~-0.785

@example
var r = deg2radf( NaN );
// returns NaN