if w0 != 0 {
		t.Fatalf("write 1200 'x's: got %d writes, want 0", w0)
	}
	io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 30))})
	if w0 != 0 {
		t.Fatalf("write 1230 'x's: got %d writes, want 0", w0)
	}
	io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 9))})
	if w0 != 1 {
		t.Fatalf("write 1239 'x's: got %d writes, want 1", w0)
	}

	var w1 writeCountingDiscard

	"path"
	"sort"
	"strings"
	"time"
)

// Writer provides sequential writing of a tar archive.
// [Writer.WriteHeader] begins a new file with the provided [Header],
// and then Writer can be treated as an io.Writer to supply that file's data.
type Writer struct {
	w    io.Writer
	pad  int64      // Amount of padding to write after current file entry
	curr fileWriter // Writer for current file entry

		var b Buffer
		b.Write(buf[0:1])
		for i := 0; i < 5<<10; i++ {
			b.Write(buf)
			b.Read(buf)
		}
	}
}

// Check that we don't compact too often. From Issue 5154.
func BenchmarkBufferFullSmallReads(b *testing.B) {
	buf := make([]byte, 1024)
	for i := 0; i < b.N; i++ {
		var b Buffer
		b.Write(buf)
		for b.Len()+20 < b.Cap() {
			b.Write(buf[:10])
		}

// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build ignore

// Mkzip writes a zoneinfo.zip with the content of the current directory
// and its subdirectories, with no compression, suitable for package time.
//
// Usage:
//
//	go run ../../mkzip.go ../../zoneinfo.zip
//

	-debug-gcc
		Debugging option. Trace C compiler execution and output.
	-dynimport file
		Write list of symbols imported by file. Write to
		-dynout argument or to standard output. Used by go
		build when building a cgo package.
	-dynlinker
		Write dynamic linker as part of -dynimport output.
	-dynout file
		Write -dynimport output to file.
	-dynpackage package
		Set Go package for -dynimport output.

	}
	for i := 0; i < chunks; i++ {
		_, err := f.Write(chunk)
		if err != nil {
			t.Fatal("write chunk:", err)
		}
	}
	if frag := int(size % chunkSize); frag > 0 {
		_, err := f.Write(chunk[:frag])
		if err != nil {
			t.Fatal("write chunk:", err)
		}
	}
	end := []byte("END\n")
	_, err = f.Write(end)
	if err != nil {
		t.Fatal("write end:", err)
	}
	if err := w.Close(); err != nil {

// accepted and all subsequent writes, and [Writer.Flush], will return the error.
// After all data has been written, the client should call the
// [Writer.Flush] method to guarantee all data has been forwarded to
// the underlying [io.Writer].
type Writer struct {
	err error
	buf []byte
	n   int
	wr  io.Writer
}

		m, e := w.Write(b.buf[b.off:])
		if m > nBytes {
			panic("bytes.Buffer.WriteTo: invalid Write count")
		}
		b.off += m
		n = int64(m)
		if e != nil {
			return n, e
		}
		// all bytes should have been written, by definition of
		// Write method in io.Writer
		if m != nBytes {
			return n, io.ErrShortWrite
		}
	}
	// Buffer is now empty; reset.
	b.Reset()
	return n, nil
}

// The print built-in function formats its arguments in an
// implementation-specific way and writes the result to standard error.
// Print is useful for bootstrapping and debugging; it is not guaranteed
// to stay in the language.
func print(args ...Type)

// The println built-in function formats its arguments in an
// implementation-specific way and writes the result to standard error.

		return formatSTAR
	case magic == magicUSTAR:
		return FormatUSTAR | FormatPAX
	case magic == magicGNU && version == versionGNU:
		return FormatGNU
	default:
		return formatV7
	}
}

// setFormat writes the magic values necessary for specified format
// and then updates the checksum accordingly.
func (b *block) setFormat(format Format) {
	// Set the magic values.
	switch {
	case format.has(formatV7):