needHeaderOffset := f.headerOffset == int64(^uint32(0))

	// Best effort to find what we need.
	// Other zip authors might not even follow the basic format,
	// and we'll just ignore the Extra content in that case.
	var modified time.Time
parseExtras:
	for extra := readBuf(f.Extra); len(extra) >= 4; { // need at least tag and size
		fieldTag := extra.uint16()
		fieldSize := int(extra.uint16())

//
// Scanning stops unrecoverably at EOF, the first I/O error, or a token too
// large to fit in the [Scanner.Buffer]. When a scan stops, the reader may have
// advanced arbitrarily far past the last token. Programs that need more
// control over error handling or large tokens, or must run sequential scans
// on a reader, should use [bufio.Reader] instead.
type Scanner struct {
	r            io.Reader // The reader provided by the client.

		[]byte("\xc0a\xc0cd"),
		[]byte("ab\xc0a\xc0")},
	{not(isValidRune), "\xc0a\xc0",
		[]byte("a"),
		[]byte("a\xc0"),
		[]byte("\xc0a")},
	// The nils returned by TrimLeftFunc are odd behavior, but we need
	// to preserve backwards compatibility.
	{isSpace, "",
		nil,
		nil,
		[]byte("")},
	{isSpace, " ",
		nil,
		nil,
		[]byte("")},
}

func TestTrimFunc(t *testing.T) {

	tok := in.Stack.Next()
	if tok != scanner.Ident {
		in.expectText("expected identifier after '#'")
	}
	if !in.enabled() {
		// Can only start including again if we are at #else or #endif but also
		// need to keep track of nested #if[n]defs.
		// We let #line through because it might affect errors.
		switch in.Stack.Text() {
		case "else", "endif", "ifdef", "ifndef", "line":
			// Press on.
		default:
			return false

		}
	})
	t.Run("uint32max-1_Zip64", func(t *testing.T) {
		t.Parallel()
		if !generatesZip64(t, gen(0xffffffff)) {
			t.Error("expected zip64")
		}
	})
}

// At 16k records, we need to generate a zip64 file.
func TestZip64ManyRecords(t *testing.T) {
	if testing.Short() {
		t.Skip("skipping in short mode")
	}
	t.Parallel()
	gen := func(numRec int) func(*Writer) {
		return func(w *Writer) {

		f.Ref = make([]*Ref, 0, 8)
	}
	f.walk(ast2, ctxProg, (*File).validateIdents)
	f.walk(ast2, ctxProg, (*File).saveExprs)

	// Accumulate exported functions.
	// The comments are only on ast1 but we need to
	// save the function bodies from ast2.
	// The first walk fills in ExpFunc, and the
	// second walk changes the entries to
	// refer to ast2 instead.
	f.walk(ast1, ctxProg, (*File).saveExport)

frame, invokes the system C function (in this case, puts), stores the
result in the frame, and returns.

Linking

Once the _cgo_export.c and *.cgo2.c files have been compiled with gcc,
they need to be linked into the final binary, along with the libraries
they might depend on (in the case of puts, stdio). cmd/link has been
extended to understand basic ELF files, but it does not understand ELF

		// The Go build system's swarming user is known not to be root.
		// Unfortunately, it sometimes appears as root due the current
		// implementation of a no-network check using 'unshare -n -r'.
		// Since this test does need root to work, we need to skip it.
		t.Skip("skipping root only test on a non-root builder")
	}
	if runtime.GOOS == "linux" {
		if _, err := os.Stat("/etc/alpine-release"); err == nil {

// operations do not read across the boundary and cause a page
// fault where they shouldn't.

// These tests run only on linux. The code being tested is
// not OS-specific, so it does not need to be tested on all
// operating systems.

// dangerousSlice returns a slice which is immediately
// preceded and followed by a faulting page.
func dangerousSlice(t *testing.T) []byte {
	pagesize := syscall.Getpagesize()

	var s scanner.Scanner
	s.Init(r)
	// Newline is like a semicolon; other space characters are fine.
	s.Whitespace = 1<<'\t' | 1<<'\r' | 1<<' '
	// Don't skip comments: we need to count newlines.
	s.Mode = scanner.ScanChars |
		scanner.ScanFloats |
		scanner.ScanIdents |
		scanner.ScanInts |
		scanner.ScanStrings |
		scanner.ScanComments
	s.Position.Filename = name