// an old zip32 file that was sharding inputs into the largest chunks
	// possible (or is just malicious; search the web for 42.zip).
	// If needUSize is true still, it means we didn't see a zip64 extension.
	// As long as the compressed size is not also 2³²-1 (implausible)
	// and the header is not also 2³²-1 (equally implausible),
	// accept the uncompressed size 2³²-1 as valid.

}

// readOldGNUSparseMap reads the sparse map from the old GNU sparse format.
// The sparse map is stored in the tar header if it's small enough.
// If it's larger than four entries, then one or more extension headers are used
// to store the rest of the sparse map.
//
// The Header.Size does not reflect the size of any extended headers used.
// Thus, this function will read from the raw io.Reader to fetch extra headers.