key ID
	val int32
	pos src.XPos
}

type sparseMapPos struct {
	dense  []sparseEntryPos
	sparse []int32
}

// newSparseMapPos returns a sparseMapPos that can map
// integers between 0 and n-1 to the pair <int32,src.XPos>.
func newSparseMapPos(n int) *sparseMapPos {
	return &sparseMapPos{dense: nil, sparse: make([]int32, n)}
}

func (s *sparseMapPos) cap() int {
	return len(s.sparse)
}

func (c *Cache) allocSparseMapPos(n int) *sparseMapPos {
	var s *sparseMapPos
	n2 := n
	if n2 < 32 {
		n2 = 32
	}
	b := bits.Len(uint(n2 - 1))
	v := poolFreeSparseMapPos[b-5].Get()
	if v == nil {
		s = newSparseMapPos(1 << b)
	} else {
		s = v.(*sparseMapPos)
	}
	return s
}
func (c *Cache) freeSparseMapPos(s *sparseMapPos) {
	s.clear()
	b := bits.Len(uint(s.cap()) - 1)

			capacity: "%s.cap()",
			mak:      "newSparseMap(%s)",
			resize:   "", // larger-sized sparse maps are ok
			clear:    "%s.clear()",
			minLog:   5,
			maxLog:   32,
		},
		{
			name:     "SparseMapPos",
			typ:      "*sparseMapPos",
			capacity: "%s.cap()",
			mak:      "newSparseMapPos(%s)",
			resize:   "", // larger-sized sparse maps are ok
			clear:    "%s.clear()",
			minLog:   5,
			maxLog:   32,
		},
	}

// newSparseMapPos returns a sparse map that can store at least up to n integers.
func (f *Func) newSparseMapPos(n int) *sparseMapPos {
	return f.Cache.allocSparseMapPos(n)
}

// retSparseMapPos returns a sparse map to the config's cache of sparse
// sets to be reused by f.newSparseMapPos.
func (f *Func) retSparseMapPos(ss *sparseMapPos) {
	f.Cache.freeSparseMapPos(ss)
}

// newPoset returns a new poset from the internal cache