code: func (r *AllocationBitmap) Release(offset int) error {
  	r.lock.Lock()
  	defer r.lock.Unlock()
  
  	if r.allocated.Bit(offset) == 0 {
  		return nil
  	}
  
  	r.allocated = r.allocated.SetBit(r.allocated, offset, 0)
  	r.count--
  	return nil
  }
docs: // Release releases the item back to the pool. Releasing an
  // unallocated item or an item out of the range is a no-op and
  // returns no error.