code: function getStartingState (cb) {
        // if we are just starting or if a chain re-org has happened
        if (!headBlock || reorg) {
          blockchain.getBlock(block.header.parentHash, function (err, parentBlock) {
            parentState = parentBlock.header.stateRoot
            // generate genesis state if we are at the genesis block
            // we don't have the genesis state
            if (!headBlock) {
              return self.stateManager.generateCanonicalGenesis(cb)
            } else {
              cb(err)
            }
          })
        } else {
          parentState = headBlock.header.stateRoot
          cb()
        }
      }
docs: determine starting state for block run