return
}

// pallocBits is a bitmap that tracks page allocations for at most one
// palloc chunk.
//
// The precise representation is an implementation detail, but for the
// sake of documentation, 0s are free pages and 1s are allocated pages.
type pallocBits pageBits

// summarize returns a packed summary of the bitmap in pallocBits.
func (b *pallocBits) summarize() pallocSum {
	var start, most, cur uint

		}
		return false
	}
	return true
}

// makePallocBits produces an initialized PallocBits by setting
// the ranges in s to 1 and the rest to zero.
func makePallocBits(s []BitRange) *PallocBits {
	b := new(PallocBits)
	for _, v := range s {
		b.AllocRange(v.I, v.N)
	}
	return b
}

// Ensures that PallocBits.AllocRange works, which is a fundamental
// method used for testing and initialization since it's used by

// Expose pallocBits for testing.
type PallocBits pallocBits

func (b *PallocBits) Find(npages uintptr, searchIdx uint) (uint, uint) {
	return (*pallocBits)(b).find(npages, searchIdx)
}
func (b *PallocBits) AllocRange(i, n uint)       { (*pallocBits)(b).allocRange(i, n) }
func (b *PallocBits) Free(i, n uint)             { (*pallocBits)(b).free(i, n) }

		if gb == nil && wb == nil {
			continue
		}
		if (gb == nil && wb != nil) || (gb != nil && wb == nil) {
			t.Errorf("chunk %d nilness mismatch", i)
		}
		if !checkPallocBits(t, gb.PallocBits(), wb.PallocBits()) {
			t.Logf("in chunk %d (mallocBits)", i)
		}
		if !checkPallocBits(t, gb.Scavenged(), wb.Scavenged()) {
			t.Logf("in chunk %d (scavenged)", i)
		}
	}
	// TODO(mknyszek): Verify summaries too?
}

	i := int(searchIdx / 64)
	// Start by quickly skipping over blocks of non-free or scavenged pages.
	for ; i >= 0; i-- {
		// 1s are scavenged OR non-free => 0s are unscavenged AND free
		x := fillAligned(m.scavenged[i]|m.pallocBits[i], uint(minimum))
		if x != ^uint64(0) {
			break
		}
	}
	if i < 0 {
		// Failed to find any free/unscavenged pages.
		return 0, 0
	}
	// We have something in the 64-bit chunk at i, but it could

	// each level fits in 64 bytes (2^3 summaries * 8 bytes per summary), which is
	// close to the L1 cache line width on many systems. Also, a value of 3 fits 4 tree
	// levels perfectly into the 21-bit pallocBits summary field at the root level.
	//
	// The following equation explains how each of the constants relate:
	// summaryL0Bits + (summaryLevels-1)*summaryLevelBits + logPallocChunkBytes = heapAddrBits
	//

	}

	mheap_.pagesSwept.Add(int64(s.npages))

	spc := s.spanclass
	size := s.elemsize

	// The allocBits indicate which unmarked objects don't need to be
	// processed since they were free at the end of the last GC cycle
	// and were not allocated since then.
	// If the allocBits index is >= s.freeindex and the bit
	// is not marked then the object remains unallocated
	// since the last GC.

	// as allocBits for newly allocated spans.
	//
	// The pointer arithmetic is done "by hand" instead of using
	// arrays to avoid bounds checks along critical performance
	// paths.
	// The sweep will free the old allocBits and set allocBits to the
	// gcmarkBits. The gcmarkBits are replaced with a fresh zeroed
	// out memory.
	allocBits  *gcBits
	gcmarkBits *gcBits

	mask  uint8
	index uintptr
}

//go:nosplit
func (s *mspan) allocBitsForIndex(allocBitIndex uintptr) markBits {
	bytep, mask := s.allocBits.bitp(allocBitIndex)
	return markBits{bytep, mask, allocBitIndex}
}

// refillAllocCache takes 8 bytes s.allocBits starting at whichByte
// and negates them so that ctz (count trailing zeros) instructions
// can be used. It then places these 8 bytes into the cached 64 bit