for _, c := range s {
		if c < 0x80 && c != 0x00 {
			b = append(b, byte(c))
		}
	}
	return string(b)
}

type parser struct {
	err error // Last error seen
}

type formatter struct {
	err error // Last error seen
}

// parseString parses bytes as a NUL-terminated C-style string.
// If a NUL byte is not found then the whole slice is returned as a string.

	var namePrefix string
	if prefix, suffix, ok := splitUSTARPath(hdr.Name); ok {
		namePrefix, hdr.Name = prefix, suffix
	}

	// Pack the main header.
	var f formatter
	blk := tw.templateV7Plus(hdr, f.formatString, f.formatOctal)
	f.formatString(blk.toUSTAR().prefix(), namePrefix)
	blk.setFormat(FormatUSTAR)
	if f.err != nil {

		copy(b.toUSTAR().version(), versionUSTAR)
	default:
		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] = ' '
}

		}
	default:
		if r.Name.Kind == "func" {
			error_(r.Pos(), "must call C.%s", fixGo(r.Name.Go))
		}
	}
	return expr
}

// gofmtPos returns the gofmt-formatted string for an AST node,
// with a comment setting the position before the node.
func gofmtPos(n ast.Expr, pos token.Pos) string {
	s := gofmtLine(n)
	p := fset.Position(pos)
	if p.Column == 0 {
		return s

		switch {
		case format.has(FormatUSTAR | FormatPAX):
			hdr.Format = format
			ustar := tr.blk.toUSTAR()
			prefix = p.parseString(ustar.prefix())

			// For Format detection, check if block is properly formatted since
			// the parser is more liberal than what USTAR actually permits.
			notASCII := func(r rune) bool { return r >= 0x80 }
			if bytes.IndexFunc(tr.blk[:], notASCII) >= 0 {