public static double normalizeRadians(double r){
  if (r < 0 && r >= -TWO_PI)   return r + TWO_PI;
  if (r >= TWO_PI && r < FOUR_PI)   return r - TWO_PI;
  if (r >= 0 && r < TWO_PI)   return r;
  r-=TWO_PI * Math.floor(r * TWO_PI_INVERSE);
  if (r < 0.)   r+=TWO_PI;
  return r;
}

public static double normalizeRadians ( double r ) { if ( r < 0 && r >= - TWO_PI ) return r + TWO_PI ; if ( r >= TWO_PI && r < FOUR_PI ) return r - TWO_PI ; if ( r >= 0 && r < TWO_PI ) return r ; r -= TWO_PI * Math . floor ( r * TWO_PI_INVERSE ) ; if ( r < 0. ) r += TWO_PI ; return r ; }
reduce an angle in radians to the range ( 0 - 2 pi ) .
