}
}

type writeUserArenaHeapBits struct {
	offset uintptr // offset in span that the low bit of mask represents the pointer state of.
	mask   uintptr // some pointer bits starting at the address addr.
	valid  uintptr // number of bits in buf that are valid (including low)
	low    uintptr // number of low-order bits to not overwrite
}

func (s *mspan) writeUserArenaHeapBits(addr uintptr) (h writeUserArenaHeapBits) {