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package main
/* Binary trie
*
* Syncronization done seperatly
* See: routing.go
*
* Todo: Better commenting
*/
type Trie struct {
cidr uint
child [2]*Trie
bits []byte
peer *Peer
// Index of "branching" bit
bit_at_byte uint
bit_at_shift uint
}
/* Finds length of matching prefix
* Maybe there is a faster way
*
* Assumption: len(s1) == len(s2)
*/
func commonBits(s1 []byte, s2 []byte) uint {
var i uint
size := uint(len(s1))
for i = 0; i < size; i += 1 {
v := s1[i] ^ s2[i]
if v != 0 {
v >>= 1
if v == 0 {
return i*8 + 7
}
v >>= 1
if v == 0 {
return i*8 + 6
}
v >>= 1
if v == 0 {
return i*8 + 5
}
v >>= 1
if v == 0 {
return i*8 + 4
}
v >>= 1
if v == 0 {
return i*8 + 3
}
v >>= 1
if v == 0 {
return i*8 + 2
}
v >>= 1
if v == 0 {
return i*8 + 1
}
return i * 8
}
}
return i * 8
}
func (node *Trie) RemovePeer(p *Peer) *Trie {
if node == nil {
return node
}
// Walk recursivly
node.child[0] = node.child[0].RemovePeer(p)
node.child[1] = node.child[1].RemovePeer(p)
if node.peer != p {
return node
}
// Remove peer & merge
node.peer = nil
if node.child[0] == nil {
return node.child[1]
}
return node.child[0]
}
func (node *Trie) choose(key []byte) byte {
return (key[node.bit_at_byte] >> node.bit_at_shift) & 1
}
func (node *Trie) Insert(key []byte, cidr uint, peer *Peer) *Trie {
// At leaf
if node == nil {
return &Trie{
bits: key,
peer: peer,
cidr: cidr,
bit_at_byte: cidr / 8,
bit_at_shift: 7 - (cidr % 8),
}
}
// Traverse deeper
common := commonBits(node.bits, key)
if node.cidr <= cidr && common >= node.cidr {
if node.cidr == cidr {
node.peer = peer
return node
}
bit := node.choose(key)
node.child[bit] = node.child[bit].Insert(key, cidr, peer)
return node
}
// Split node
newNode := &Trie{
bits: key,
peer: peer,
cidr: cidr,
bit_at_byte: cidr / 8,
bit_at_shift: 7 - (cidr % 8),
}
cidr = min(cidr, common)
// Check for shorter prefix
if newNode.cidr == cidr {
bit := newNode.choose(node.bits)
newNode.child[bit] = node
return newNode
}
// Create new parent for node & newNode
parent := &Trie{
bits: key,
peer: nil,
cidr: cidr,
bit_at_byte: cidr / 8,
bit_at_shift: 7 - (cidr % 8),
}
bit := parent.choose(key)
parent.child[bit] = newNode
parent.child[bit^1] = node
return parent
}
func (node *Trie) Lookup(key []byte) *Peer {
var found *Peer
size := uint(len(key))
for node != nil && commonBits(node.bits, key) >= node.cidr {
if node.peer != nil {
found = node.peer
}
if node.bit_at_byte == size {
break
}
bit := node.choose(key)
node = node.child[bit]
}
return found
}
func (node *Trie) Count() uint {
if node == nil {
return 0
}
l := node.child[0].Count()
r := node.child[1].Count()
return l + r
}
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