code: func intPow(x, y int) (r int) {
  	if x == r || y < r {
  		return
  	}
  	r = 1
  	if x == r {
  		return
  	}
  	if x < 0 {
  		x = -x
  		if y&1 == 1 {
  			r = -1
  		}
  	}
  	for y > 0 {
  		if y&1 == 1 {
  			r *= x
  		}
  		x *= x
  		y >>= 1
  	}
  	return
  }
docs: // intPow returns x**y, the base-x exponential of y.