jch.go

type ShardRouter struct {
	nh         runtime.IHost
	logger     zerolog.Logger
	hasher     hash.Hash64 // fnv.New64a() since we need fast, not secure
	shardCount atomic.Int64
}

// CalcShard is an implementation of Jump Consistent Hash. It computes a string key and returns the shard the key can be
// found in.
// ref: https://arxiv.org/ftp/arxiv/papers/1406/1406.2294.pdf
func (s *ShardRouter) CalcShard(key []byte) (uint64, error) {

	s.hasher.Reset()
	_, err := s.hasher.Write(key)
	if err != nil {
		return 0, err
	}
	h := s.hasher.Sum64()

	// todo (sienna): I know there's a bug here, I just can't find it
	if s.shardCount.Load() == 0 {
		s.shardCount.Store(1)
	}

	var b, j int64
	for j < s.shardCount.Load() {
		b = j
		h = h*2862933555777941757 + 1
		j = int64(float64(b+1) * (float64(int64(1)<<31) / float64((h>>33)+1)))
	}

	return h, nil
}