i := (addr - span.base()) / goarch.PtrSize / ptrBits
	j := (addr - span.base()) / goarch.PtrSize % ptrBits
	bits := span.elemsize / goarch.PtrSize
	word0 := (*uintptr)(unsafe.Pointer(addb(hbits, goarch.PtrSize*(i+0))))
	word1 := (*uintptr)(unsafe.Pointer(addb(hbits, goarch.PtrSize*(i+1))))

	var read uintptr
	if j+bits > ptrBits {
		// Two reads.
		bits0 := ptrBits - j
		bits1 := bits - bits0
		read = *word0 >> j

	// due to one of the throws below shows the original block
	// base and extent.
	b := b0
	n := n0

	for i := uintptr(0); i < n; {
		// Find bits for the next word.
		bits := uint32(*addb(ptrmask, i/(goarch.PtrSize*8)))
		if bits == 0 {
			i += goarch.PtrSize * 8
			continue
		}
		for j := 0; j < 8 && i < n; j++ {
			if bits&1 != 0 {
				// Same work as in scanobject; see comments there.