panic("invalid format")
	}

	// Update checksum.
	// This field is special in that it is terminated by a NULL then space.
	var f formatter
	field := b.toV7().chksum()
	chksum, _ := b.computeChecksum() // Possible values are 256..128776
	f.formatOctal(field[:7], chksum) // Never fails since 128776 < 262143
	field[7] = ' '
}

// computeChecksum computes the checksum for the header block.

		}
	}()
	wg.Wait()

	sobj.Close()
	tobj.Close()

	if !sourceFailed && !targetFailed {
		ssum := srcSha256.Sum(nil)
		tsum := tgtSha256.Sum(nil)
		allgood = bytes.Equal(ssum, tsum)
		if !allgood {
			fmt.Printf("sha256 sum mismatch: %s -> Expected(%x), Found(%x)\n", srcCtnt.Key, ssum, tsum)
		}
	}

	return allgood