code: func (ms *FileMsgStore) getFileSliceForSeq(seq uint64) *fileSlice {
  	if len(ms.files) == 0 {
  		return nil
  	}
  	// Start with write slice
  	slice := ms.writeSlice
  	if (slice.firstSeq <= seq) && (seq <= slice.lastSeq) {
  		return slice
  	}
  	// We want to support possible gaps in file slice sequence, so
  	// no dichotomy, but simple iteration of the map, which in Go is
  	// random.
  	for _, slice := range ms.files {
  		if (slice.firstSeq <= seq) && (seq <= slice.lastSeq) {
  			return slice
  		}
  	}
  	return nil
  }
docs: // getFileSliceForSeq returns the file slice where the message of the
  // given sequence is stored, or nil if the message is not found in any
  // of the file slices.