distributionSha256Result=true
    fi
  elif command -v shasum >/dev/null; then
    if echo "$distributionSha256Sum  $TMP_DOWNLOAD_DIR/$distributionUrlName" | shasum -a 256 -c >/dev/null 2>&1; then
      distributionSha256Result=true
    fi
  else
    echo "Checksum validation was requested but neither 'sha256sum' or 'shasum' are available." >&2

		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.

	SHA1H V17, V25                                              // 390a285e
	SHA1M V0.S4, V27, V27                                       // 7b23005e
	SHA1P V3.S4, V20, V27                                       // 9b12035e
	SHA1SU0 V17.S4, V13.S4, V16.S4                              // b031115e
	SHA1SU1 V24.S4, V23.S4                                      // 171b285e

    /**
     * A map of patterns to prefix, used to find the LICENSE and NOTICE file.
     */
    private Map<String, String> mappings = new LinkedHashMap<>();

    /**
     * Names of dependencies whose shas should not exist.
     */
    private Set<String> ignoreShas = new HashSet<>();

    /**
     *  Names of files that should be ignored by the check
     */