//
	// We can convert that to the following logic: add 1 if remainder > q/2,
	// then add 1 again if remainder > q + q/2.
	//
	// Note that if remainder > x, then ⌊x⌋ - remainder underflows, and the top
	// bit of the difference will be set.
	quotient += (q/2 - remainder) >> 31 & 1
	quotient += (q + q/2 - remainder) >> 31 & 1

	// quotient might have overflowed at this point, so reduce it by masking.

    checkState(xSumOfSquaresOfDeltas > 0.0);
    checkState(ySumOfSquaresOfDeltas > 0.0);
    // The product of two positive numbers can be zero if the multiplication underflowed. We
    // force a positive value by effectively rounding up to MIN_VALUE.
    double productOfSumsOfSquaresOfDeltas =
        ensurePositive(xSumOfSquaresOfDeltas * ySumOfSquaresOfDeltas);

	// It's not the full required semantics, but should handle the case
	// of calling Getdirentries or ReadDirent repeatedly.
	// It won't handle assigning the results of lseek to *basep, or handle
	// the directory being edited underfoot.
	skip, err := Seek(fd, 0, 1 /* SEEK_CUR */)
	if err != nil {
		return 0, err
	}

	// We need to duplicate the incoming file descriptor
	// because the caller expects to retain control of it, but

    checkState(xSumOfSquaresOfDeltas > 0.0);
    checkState(ySumOfSquaresOfDeltas > 0.0);
    // The product of two positive numbers can be zero if the multiplication underflowed. We
    // force a positive value by effectively rounding up to MIN_VALUE.
    double productOfSumsOfSquaresOfDeltas =
        ensurePositive(xSumOfSquaresOfDeltas * ySumOfSquaresOfDeltas);

	if err := t.checkCanParse(); err != nil {
		return nil, err
	}

	ret, err := t.text.Parse(text)
	if err != nil {
		return nil, err
	}

	// In general, all the named templates might have changed underfoot.
	// Regardless, some new ones may have been defined.
	// The template.Template set has been updated; update ours.
	t.nameSpace.mu.Lock()
	defer t.nameSpace.mu.Unlock()
	for _, v := range ret.Templates() {

	// to a lockedSource.
	// Either way we do the same thing.

	r := New(new(lockedSource))
	r.Seed(seed)

	if !globalRandGenerator.CompareAndSwap(orig, r) {
		// Something changed underfoot. Retry to be safe.
		Seed(seed)
	}
}

// Int63 returns a non-negative pseudo-random 63-bit integer as an int64
// from the default [Source].
func Int63() int64 { return globalRand().Int63() }

	if err != nil {
		return 0, fmt.Errorf("reading tree: %v\ntree:\n%s", err, note.Text)
	}

	// Other lookups may be calling mergeLatest with other heads,
	// so c.latest is changing underfoot. We don't want to hold the
	// c.mu lock during tile fetches, so loop trying to update c.latest.
	c.latestMu.Lock()
	latest := c.latest
	latestMsg := c.latestMsg
	c.latestMu.Unlock()

	for {

func (b *profBuf) incrementOverflow(now int64) {
	for {
		overflow := b.overflow.Load()

		// Once we see b.overflow reach 0, it's stable: no one else is changing it underfoot.
		// We need to set overflowTime if we're incrementing b.overflow from 0.
		if uint32(overflow) == 0 {
			// Store overflowTime first so it's always available when overflow != 0.
			b.overflowTime.Store(uint64(now))

	if _, err := file.Read(buf); err != nil {
		f.Truncate(0)
		return err
	}
	h.Write(buf)
	sum := h.Sum(nil)
	if !bytes.Equal(sum, out[:]) {
		f.Truncate(0)
		return fmt.Errorf("file content changed underfoot")
	}

	// Commit cache file entry.
	if _, err := f.Write(buf); err != nil {
		f.Truncate(0)
		return err
	}
	if err := f.Close(); err != nil {
		// Data might not have been written,

	// It's not the full required semantics, but should handle the case
	// of calling Getdirentries or ReadDirent repeatedly.
	// It won't handle assigning the results of lseek to *basep, or handle
	// the directory being edited underfoot.
	skip, err := Seek(fd, 0, 1 /* SEEK_CUR */)
	if err != nil {
		return 0, err
	}

	// We need to duplicate the incoming file descriptor
	// because the caller expects to retain control of it, but