code: public ComplexFloat muli(ComplexFloat c, ComplexFloat result) {
      float newR = r * c.r - i * c.i;
      float newI = r * c.i + i * c.r;
      result.r = newR;
      result.i = newI;
      return result;
    }
docs: Multiply two complex numbers, in-place
  
  @param c      other complex number
  @param result complex number where product is stored
  @return same as result