s.largeType.PtrBytes = uintptr(ptr) - base + typ.PtrBytes

	// Double-check that the bitmap was written out correctly.
	const doubleCheck = false
	if doubleCheck {
		doubleCheckHeapPointersInterior(uintptr(ptr), uintptr(ptr), typ.Size_, typ.Size_, typ, &s.largeType, s)
	}
}

type writeUserArenaHeapBits struct {
	offset uintptr // offset in span that the low bit of mask represents the pointer state of.