// See if we have enough space in the mmaped area.
	bufLen := int64(len(out.buf))
	if out.off+lenToWrite <= bufLen {
		return out.off, out.buf
	}

	// Not enough space in the mmaped area, write to heap area instead.
	heapPos := out.off - bufLen
	heapLen := int64(len(out.heap))
	lenNeeded := heapPos + lenToWrite
	if lenNeeded > heapLen { // do we need to grow the heap storage?

	UsageLine: "go telemetry [off|local|on]",
	Short:     "manage telemetry data and settings",
	Long: `Telemetry is used to manage Go telemetry data and settings.

Telemetry can be in one of three modes: off, local, or on.

When telemetry is in local mode, counter data is written to the local file
system, but will not be uploaded to remote servers.

When telemetry is off, local counter data is neither collected nor uploaded.

	// Test PCToLine
	sym := tab.LookupFunc("main.linefrompc")
	wantLine := 0
	for pc := sym.Entry; pc < sym.End; pc++ {
		off := pc - text.Addr // TODO(rsc): should not need off; bug in 8g
		if textdat[off] == 255 {
			break
		}
		wantLine += int(textdat[off])
		t.Logf("off is %d %#x (max %d)", off, textdat[off], sym.End-pc)
		file, line, fn := tab.PCToLine(pc)
		if fn == nil {
			t.Errorf("failed to get line of PC %#x", pc)

    checkNotNull(str);
    checkNotClosed();
    target.append(str);
  }

  @Override
  public void write(String str, int off, int len) throws IOException {
    checkNotNull(str);
    checkNotClosed();
    // tricky: append takes start, end pair...
    target.append(str, off, off + len);
  }

  @Override
  public void flush() throws IOException {
    checkNotClosed();
    if (target instanceof Flushable) {

	}

	br.backup()

	if err := r.buildFSE(off, norm[:maxSym+1], table, accuracyLog); err != nil {
		return 0, 0, err
	}

	return accuracyLog, int(br.off), nil
}

// buildFSE builds an FSE decoding table from a list of probabilities.
// The probabilities are in norm. next is scratch space. The number of bits
// in the table is tableBits.
func (r *Reader) buildFSE(off int, norm []int16, table []fseEntry, tableBits int) error {

  /**
   * Puts a chunk of an array of bytes into this sink. {@code bytes[off]} is the first byte written,
   * {@code bytes[off + len - 1]} is the last.
   *
   * @param bytes a byte array
   * @param off the start offset in the array
   * @param len the number of bytes to write
   * @return this instance
   * @throws IndexOutOfBoundsException if {@code off < 0} or {@code off + len > bytes.length} or
   *     {@code len < 0}
   */

  /**
   * This method will be called for each chunk of bytes in an input stream. The implementation
   * should process the bytes from {@code buf[off]} through {@code buf[off + len - 1]} (inclusive).
   *
   * @param buf the byte array containing the data to process
   * @param off the initial offset into the array
   * @param len the length of data to be processed
   * @return true to continue processing, false to stop
   */

  /**
   * This method will be called for each chunk of bytes in an input stream. The implementation
   * should process the bytes from {@code buf[off]} through {@code buf[off + len - 1]} (inclusive).
   *
   * @param buf the byte array containing the data to process
   * @param off the initial offset into the array
   * @param len the length of data to be processed
   * @return true to continue processing, false to stop
   */

		// an errno value.
		var ret uintptr
		systemstack(func() {
			ret = callCgoMmap(addr, n, prot, flags, fd, off)
		})
		if ret < 4096 {
			return nil, int(ret)
		}
		return unsafe.Pointer(ret), 0
	}
	return sysMmap(addr, n, prot, flags, fd, off)
}

func munmap(addr unsafe.Pointer, n uintptr) {
	if _cgo_munmap != nil {
		systemstack(func() { callCgoMunmap(addr, n) })
		return
	}

env home=$WORK/userconfig # plan9
[GOOS:plan9] env userconfig=$home/lib

go telemetry
stdout 'local'

go telemetry off
go telemetry
stdout 'off'
go env GOTELEMETRY
stdout 'off'

go telemetry local
go telemetry
stdout 'local'
go env GOTELEMETRY
stdout 'local'

go telemetry on
go telemetry
stdout 'on'
go env GOTELEMETRY
stdout 'on'