t.Errorf("test %d, unexpected WriteHeader error: %v", i, err)
		}
		if err := tw.Close(); err != nil {
			t.Errorf("test %d, unexpected Close error: %v", i, err)
		}

		// The prefix field should never appear in the GNU format.
		var blk block
		copy(blk[:], b.Bytes())
		prefix := string(blk.toUSTAR().prefix())
		prefix, _, _ = strings.Cut(prefix, "\x00") // Truncate at the NUL terminator

				Name:   "foo",
				Method: Deflate,
			})
			w.Write(bigBuf)
		}
		zw.Close()
	}

	b.ReportAllocs()
	// Run once and then reset the timer.
	// This effectively discards the very large initial flate setup cost,
	// as well as the initialization of bigBuf.
	runOnce(&bytes.Buffer{})
	b.ResetTimer()

	b.RunParallel(func(pb *testing.PB) {
		var buf bytes.Buffer
		for pb.Next() {