if d.directorySize > maxInt64 || d.directoryOffset > maxInt64 {
		return nil, 0, ErrFormat
	}

	baseOffset = directoryEndOffset - int64(d.directorySize) - int64(d.directoryOffset)

	// Make sure directoryOffset points to somewhere in our file.
	if o := baseOffset + int64(d.directoryOffset); o < 0 || o >= size {
		return nil, 0, ErrFormat
	}

	// If the directory end data tells us to use a non-zero baseOffset,

// Thus, this function will read from the raw io.Reader to fetch extra headers.
// This method mutates blk in the process.
func (tr *Reader) readOldGNUSparseMap(hdr *Header, blk *block) (sparseDatas, error) {
	// Make sure that the input format is GNU.
	// Unfortunately, the STAR format also has a sparse header format that uses
	// the same type flag but has a completely different layout.
	if blk.getFormat() != FormatGNU {