function floor( x ) {
	return addon( x );
}
Rounds a double-precision floating-point number toward negative infinity.

@private
@param {number} x - input value
@returns {number} rounded value

@example
var v = floor( -4.2 );
// returns -5.0

@example
var v = floor( 9.99999 );
// returns 9.0

@example
var v = floor( 0.0 );
// returns 0.0

@example
var v = floor( NaN );
// returns NaN