2 files changed, 203 insertions, 0 deletions
diff --git a/core/types/nodeset.go b/core/types/nodeset.go
new file mode 100644
index 0000000..9025cd7
--- /dev/null
+++ b/core/types/nodeset.go
@@ -0,0 +1,144 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package types
+
+import (
+	"container/heap"
+	"encoding/binary"
+	"math/big"
+
+	"github.com/dexon-foundation/dexon-consensus-core/core/crypto"
+)
+
+// NodeSet is the node set structure as defined in DEXON consensus core.
+type NodeSet struct {
+	Nodes map[NodeID]struct{}
+}
+
+// SubSetTarget is the sub set target for GetSubSet().
+type SubSetTarget *big.Int
+
+type subSetTargetType byte
+
+const (
+	targetNotarySet subSetTargetType = iota
+	targetWitnessSet
+	targetDKGSet
+)
+
+type nodeRank struct {
+	ID   NodeID
+	rank *big.Int
+}
+
+// rankHeap is a MaxHeap structure.
+type rankHeap []*nodeRank
+
+func (h rankHeap) Len() int           { return len(h) }
+func (h rankHeap) Less(i, j int) bool { return h[i].rank.Cmp(h[j].rank) > 0 }
+func (h rankHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+func (h *rankHeap) Push(x interface{}) {
+	*h = append(*h, x.(*nodeRank))
+}
+func (h *rankHeap) Pop() interface{} {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+// NewNodeSet creates a new NodeSet instance.
+func NewNodeSet() *NodeSet {
+	return &NodeSet{
+		Nodes: make(map[NodeID]struct{}),
+	}
+}
+
+// NewNotarySetTarget is the target for getting Notary Set.
+func NewNotarySetTarget(crs []byte, shardID, chainID uint32) SubSetTarget {
+	binaryShardID := make([]byte, 4)
+	binary.LittleEndian.PutUint32(binaryShardID, shardID)
+
+	binaryChainID := make([]byte, 4)
+	binary.LittleEndian.PutUint32(binaryChainID, chainID)
+
+	return newTarget(targetNotarySet, crs, binaryShardID, binaryChainID)
+}
+
+// NewWitnessSetTarget  is the target for getting DKG Set.
+func NewWitnessSetTarget(crs []byte, round uint64) SubSetTarget {
+	binaryRound := make([]byte, 8)
+	binary.LittleEndian.PutUint64(binaryRound, round)
+
+	return newTarget(targetWitnessSet, crs, binaryRound)
+}
+
+// NewDKGSetTarget  is the target for getting DKG Set.
+func NewDKGSetTarget(crs []byte, round uint64) SubSetTarget {
+	binaryRound := make([]byte, 8)
+	binary.LittleEndian.PutUint64(binaryRound, round)
+
+	return newTarget(targetDKGSet, crs, binaryRound)
+}
+
+// GetSubSet returns the subset of given target.
+func (ns *NodeSet) GetSubSet(size int, target SubSetTarget) NodeIDs {
+	h := rankHeap{}
+	idx := 0
+	for nID := range ns.Nodes {
+		if idx < size {
+			h = append(h, newNodeRank(nID, target))
+		} else if idx == size {
+			heap.Init(&h)
+		}
+		if idx >= size {
+			rank := newNodeRank(nID, target)
+			if rank.rank.Cmp(h[0].rank) < 0 {
+				h[0] = rank
+				heap.Fix(&h, 0)
+			}
+		}
+		idx++
+	}
+
+	nIDs := make(NodeIDs, 0, size)
+	for _, rank := range h {
+		nIDs = append(nIDs, rank.ID)
+	}
+
+	return nIDs
+}
+
+func newTarget(targetType subSetTargetType, data ...[]byte) SubSetTarget {
+	data = append(data, []byte{byte(targetType)})
+	h := crypto.Keccak256Hash(data...)
+	num := big.NewInt(0)
+	num.SetBytes(h[:])
+	return SubSetTarget(num)
+}
+
+func newNodeRank(ID NodeID, target SubSetTarget) *nodeRank {
+	num := big.NewInt(0)
+	num.SetBytes(ID.Hash[:])
+	num.Abs(num.Sub((*big.Int)(target), num))
+	return &nodeRank{
+		ID:   ID,
+		rank: num,
+	}
+}
diff --git a/core/types/nodeset_test.go b/core/types/nodeset_test.go
new file mode 100644
index 0000000..6fe9092
--- /dev/null
+++ b/core/types/nodeset_test.go
@@ -0,0 +1,59 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package types
+
+import (
+	"testing"
+
+	"github.com/dexon-foundation/dexon-consensus-core/common"
+	"github.com/stretchr/testify/suite"
+)
+
+type NodeSetTestSuite struct {
+	suite.Suite
+}
+
+func (s *NodeSetTestSuite) TestGetSubSet() {
+	total := 10
+	crs := common.NewRandomHash()
+	nodes := NewNodeSet()
+	for len(nodes.Nodes) < total {
+		nodes.Nodes[NodeID{common.NewRandomHash()}] = struct{}{}
+	}
+	target := NewNotarySetTarget(crs[:], 0, 0)
+	ranks := make(map[NodeID]*nodeRank, len(nodes.Nodes))
+	for nID := range nodes.Nodes {
+		ranks[nID] = newNodeRank(nID, target)
+	}
+	size := 4
+	notarySet := nodes.GetSubSet(size, target)
+	for _, notary := range notarySet {
+		win := 0
+		rank := ranks[notary].rank
+		for node := range nodes.Nodes {
+			if rank.Cmp(ranks[node].rank) < 0 {
+				win++
+			}
+		}
+		s.True(win >= total-size)
+	}
+}
+
+func TestNodeSet(t *testing.T) {
+	suite.Run(t, new(NodeSetTestSuite))
+}