}
	freeByteBase := s.freeindex &^ (64 - 1)
	whichByte := freeByteBase / 8
	// Init alloc bits cache.
	s.refillAllocCache(whichByte)

	// Adjust the allocCache so that s.freeindex corresponds to the low bit in
	// s.allocCache.
	s.allocCache >>= s.freeindex % 64

	return s
}

// Return span from an mcache.
//
// s must have a span class corresponding to this
// mcentral and it must not be empty.

		// As each 1 in s.allocCache was encountered and used for allocation
		// it was shifted away. At this point s.allocCache contains all 0s.
		// Refill s.allocCache so that it corresponds
		// to the bits at s.allocBits starting at s.freeindex.
		whichByte := sfreeindex / 8
		s.refillAllocCache(whichByte)
	}
	s.freeindex = sfreeindex
	return result
}

	freeIndexForScan uint16

	// Cache of the allocBits at freeindex. allocCache is shifted
	// such that the lowest bit corresponds to the bit freeindex.
	// allocCache holds the complement of allocBits, thus allowing
	// ctz (count trailing zero) to use it directly.
	// allocCache may contain bits beyond s.nelems; the caller must ignore
	// these.
	allocCache uint64

	// allocBits and gcmarkBits hold pointers to a span's mark and

func nextFreeFast(s *mspan) gclinkptr {
	theBit := sys.TrailingZeros64(s.allocCache) // Is there a free object in the allocCache?
	if theBit < 64 {
		result := s.freeindex + uint16(theBit)
		if result < s.nelems {
			freeidx := result + 1
			if freeidx%64 == 0 && freeidx != s.nelems {
				return 0
			}
			s.allocCache >>= uint(theBit + 1)
			s.freeindex = freeidx
			s.allocCount++

}

type stackfreelist struct {
	list gclinkptr // linked list of free stacks
	size uintptr   // total size of stacks in list
}

// dummy mspan that contains no free objects.
var emptymspan mspan

func allocmcache() *mcache {
	var c *mcache
	systemstack(func() {
		lock(&mheap_.lock)
		c = (*mcache)(mheap_.cachealloc.alloc())
		c.flushGen.Store(mheap_.sweepgen)
		unlock(&mheap_.lock)
	})
	for i := range c.alloc {

			if mcache0 == nil {
				throw("missing mcache?")
			}
			// Use the bootstrap mcache0. Only one P will get
			// mcache0: the one with ID 0.
			pp.mcache = mcache0
		} else {
			pp.mcache = allocmcache()
		}
	}
	if raceenabled && pp.raceprocctx == 0 {
		if id == 0 {
			pp.raceprocctx = raceprocctx0
			raceprocctx0 = 0 // bootstrap
		} else {
			pp.raceprocctx = raceproccreate()
		}