code: func expand(buf []byte, l int) []byte {
  	c := (cap(buf) + 1) * 3 / 2
  	for l > c {
  		c = (c + 1) * 3 / 2
  	}
  	new := MakeAlignedByteSliceCap(len(buf), c)
  	copy(new, buf)
  	return new
  }
docs: // Expand the array underlying a slice to have capacity of at least l