// minus any inline space for metadata.
func roundupsize(size uintptr, noscan bool) (reqSize uintptr) {
	reqSize = size
	if reqSize <= maxSmallSize-mallocHeaderSize {
		// Small object.
		if !noscan && reqSize > minSizeForMallocHeader { // !noscan && !heapBitsInSpan(reqSize)
			reqSize += mallocHeaderSize
		}

	// For goarch.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
	// For powers of 2, use a variable shift.
	noscan := !et.Pointers()
	switch {
	case et.Size_ == 1:
		lenmem = uintptr(oldLen)
		newlenmem = uintptr(newLen)
		capmem = roundupsize(uintptr(newcap), noscan)
		overflow = uintptr(newcap) > maxAlloc
		newcap = int(capmem)
	case et.Size_ == goarch.PtrSize:

		span = c.allocLarge(size, noscan)
		span.freeindex = 1
		span.allocCount = 1
		size = span.elemsize
		x = unsafe.Pointer(span.base())
		if needzero && span.needzero != 0 {
			delayedZeroing = true
		}
		if !noscan {
			// Tell the GC not to look at this yet.
			span.largeType = nil
			header = &span.largeType
		}
	}
	if !noscan && !delayedZeroing {

	c.scanAlloc = 0

	c.alloc[spc] = s
}

// allocLarge allocates a span for a large object.
func (c *mcache) allocLarge(size uintptr, noscan bool) *mspan {
	if size+_PageSize < size {
		throw("out of memory")
	}
	npages := size >> _PageShift
	if size&_PageMask != 0 {
		npages++
	}

	// Deduct credit for this span allocation and sweep if

		}
	}
	h.allspans = h.allspans[:len(h.allspans)+1]
	h.allspans[len(h.allspans)-1] = s
}

// A spanClass represents the size class and noscan-ness of a span.
//
// Each size class has a noscan spanClass and a scan spanClass. The
// noscan spanClass contains only noscan objects, which do not contain
// pointers and thus do not need to be scanned by the garbage
// collector.
type spanClass uint8

const (

//
// The sweeper handles moving chunks out of this quarantine state to be ready for
// reuse. When the chunk is placed into the quarantine state, its corresponding
// span is marked as noscan so that the GC doesn't try to scan memory that would
// cause a fault.
//
// At the next layer are the user arenas themselves. They consist of a single
// active chunk which new Go values are bump-allocated into and a list of chunks

	s := spanOfUnchecked(b)
	n := s.elemsize
	if n == 0 {
		throw("scanobject n == 0")
	}
	if s.spanclass.noscan() {
		// Correctness-wise this is ok, but it's inefficient
		// if noscan objects reach here.
		throw("scanobject of a noscan object")
	}

	var tp typePointers
	if n > maxObletBytes {
		// Large object. Break into oblets for better
		// parallelism and lower latency.

//
//go:nosplit
func (span *mspan) heapBits() []uintptr {
	const doubleCheck = false

	if doubleCheck && !span.isUserArenaChunk {
		if span.spanclass.noscan() {
			throw("heapBits called for noscan")
		}
		if span.elemsize > minSizeForMallocHeader {
			throw("heapBits called for span class that should have a malloc header")
		}
	}
	// Find the bitmap at the end of the span.
	//

		// Mark span.
		arena, pageIdx, pageMask := pageIndexOf(span.base())
		if arena.pageMarks[pageIdx]&pageMask == 0 {
			atomic.Or8(&arena.pageMarks[pageIdx], pageMask)
		}

		if span.spanclass.noscan() {
			gcw.bytesMarked += uint64(span.elemsize)
			continue
		}
		ptrs[pos] = obj
		pos++
	}

	// Enqueue the greyed objects.
	gcw.putBatch(ptrs[:pos])

	pp.wbBuf.reset()

		if isGoPointerWithoutSpan(e.data) {
			return
		}
		throw("runtime.SetFinalizer: pointer not in allocated block")
	}

	// Move base forward if we've got an allocation header.
	if !span.spanclass.noscan() && !heapBitsInSpan(span.elemsize) && span.spanclass.sizeclass() != 0 {
		base += mallocHeaderSize
	}

	if uintptr(e.data) != base {
		// As an implementation detail we allow to set finalizers for an inner byte