return f
	}

	s.mutex.RLock()
	defer s.mutex.RUnlock()

	// p is not in last file - search all files
	if i := searchFiles(s.files, int(p)); i >= 0 {
		f := s.files[i]
		// f.base <= int(p) by definition of searchFiles
		if int(p) <= f.base+f.size {
			// Update cache of last file. A race is ok,
			// but an exclusive lock causes heavy contention.
			s.last.Store(f)
			return f