use compact node arrays
although this does reduce the amount of memory allocated during Set by more than half, it doubles the number of allocations and doesn't seem to impact the runtime. frustrating.master
parent
6de290647d
commit
82711582b1
86
pmap.go
86
pmap.go
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@ -29,10 +29,18 @@ type pmap struct {
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// A Map implemented as a hashed trie
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type node struct {
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child [nodeDegree]interface{}
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child []interface{}
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bitmap uint32
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}
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func bitmask(shiftedHash uint32) uint32 {
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return uint32(1) << (shiftedHash & nodeMask)
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}
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func (n *node) index(mask uint32) int {
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return bits.OnesCount32(n.bitmap & (mask - 1))
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}
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type collision struct {
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hash uint32
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leaf []leaf
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@ -77,18 +85,28 @@ func (p pmap) Del(k Key) Map {
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return p
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}
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func (m *node) getNode(shift, hash uint32, key Key) interface{} {
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i := hash >> shift & nodeMask
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return m.child[i]
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func (n *node) check() {
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if bits.OnesCount32(n.bitmap) != len(n.child) {
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panic(fmt.Sprintf("pmap: corrupt bitmap b=%#b len=%d", n.bitmap, len(n.child)))
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}
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}
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func (m collision) getNode(hash uint32, key Key) interface{} {
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if hash != m.hash {
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func (n *node) getNode(shift, hash uint32, key Key) interface{} {
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n.check()
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m := bitmask(hash >> shift)
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if n.bitmap&m == 0 {
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return nil
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}
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for i := range m.leaf {
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if key == m.leaf[i].k {
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return m.leaf[i]
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return n.child[n.index(m)]
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}
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func (n collision) getNode(hash uint32, key Key) interface{} {
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if hash != n.hash {
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return nil
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}
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for i := range n.leaf {
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if key == n.leaf[i].k {
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return n.leaf[i]
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}
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}
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return nil
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@ -123,9 +141,10 @@ func singleton(key Key, val Value, hash, shift uint32) *node {
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func newnode(child interface{}, hash, shift uint32) *node {
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n := &node{}
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idx := hash >> shift & nodeMask
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n.child[idx] = child
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n.bitmap = 1 << idx
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a := [1]interface{}{child}
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n.child = a[:]
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n.bitmap = bitmask(hash >> shift)
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n.check()
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return n
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}
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@ -155,8 +174,8 @@ func insert(n interface{}, hash uint32, key Key, val Value, hashFn HashFunc) (ne
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}
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// not a collision, so we must still have some hash bits left
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// split the trie
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m := newnode(n, h, shift)
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return _insert(m, shift)
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x := newnode(n, h, shift)
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return _insert(x, shift)
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}
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case *node:
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c := n.getNode(shift, hash, key)
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@ -164,28 +183,42 @@ func insert(n interface{}, hash uint32, key Key, val Value, hashFn HashFunc) (ne
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// new node
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c = leaf{key, val}
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added = true
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m := bitmask(hash >> shift)
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x := &node{bitmap: n.bitmap | m}
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i := x.index(m)
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x.child = make([]interface{}, len(n.child)+1)
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copy(x.child[:i], n.child[:i])
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x.child[i] = c
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copy(x.child[i+1:], n.child[i:])
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x.check()
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return x
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} else {
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c = _insert(c, shift+nodeShift)
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}
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idx := hash >> shift & nodeMask
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x := &node{child: n.child, bitmap: n.bitmap}
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x.child[idx] = c
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x.bitmap |= 1 << idx
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// TODO: short circuit if c unchanged?
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m := bitmask(hash >> shift)
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x := &node{bitmap: n.bitmap}
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i := x.index(m)
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x.child = make([]interface{}, len(n.child))
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copy(x.child, n.child)
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x.child[i] = c
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x.check()
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return x
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}
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case collision:
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if n.hash != hash {
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// not a collision, so we must still have some hash bits left
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// split the trie
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m := newnode(n, n.hash, shift)
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return _insert(m, shift)
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x := newnode(n, n.hash, shift)
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return _insert(x, shift)
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}
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for i := range n.leaf {
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if key == n.leaf[i].k {
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// replace existing entry
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l := make([]leaf, 1, len(n.leaf))
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l := make([]leaf, len(n.leaf))
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l[0] = leaf{key, val}
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l = append(l, n.leaf[:i]...)
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l = append(l, n.leaf[i+1:]...)
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copy(l[1:], n.leaf[:i])
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copy(l[1+i:], n.leaf[i+1:])
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added = false
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return collision{hash, l}
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}
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@ -230,11 +263,12 @@ func (p pmap) stats() stats {
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case *node:
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s.count++
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s.nodeCount++
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s.emptySlots += bits.OnesCount32(^n.bitmap)
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td += float64(bits.OnesCount32(n.bitmap))
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for i := range n.child {
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if n.child[i] != nil {
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td += 1.0
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visit(n.child[i], h+1)
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} else {
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s.emptySlots++
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}
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}
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case collision:
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17
pmap_test.go
17
pmap_test.go
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@ -12,6 +12,8 @@ func hash(k Key) uint32 {
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return uint32(u + u>>32)
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}
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// FIXME: collisions can cause allocations during Get
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func TestPmap(t *testing.T) {
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p := New(hash)
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const numElems = 100
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@ -172,3 +174,18 @@ func benchmarkHmapSet(b *testing.B, numElems int) {
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delete(h, k)
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}
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}
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func TestBitmap(t *testing.T) {
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n := node{bitmap: 0xff0a}
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const x = -1
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want := []int{x, 0, x, 1, x, x, x, x, 2, 3, 4, 5, 6, 7, 8, 9}
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for i, j := range want {
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if j == x {
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continue
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}
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m := bitmask(uint32(i))
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if got := n.index(m); got != j {
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t.Errorf("got %v, want %v", got, j)
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}
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}
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}
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