b.data = make([]uint64, bufwords)
	b.tags = make([]unsafe.Pointer, tags)
	b.overflowBuf = make([]uint64, 2+b.hdrsize+1)
	return b
}

// canWriteRecord reports whether the buffer has room
// for a single contiguous record with a stack of length nstk.
func (b *profBuf) canWriteRecord(nstk int) bool {
	br := b.r.load()
	bw := b.w.load()

	// room for tag?
	if countSub(br.tagCount(), bw.tagCount())+len(b.tags) < 1 {