proveVoteTallyBatch() may fail on the final batch

[weijiekoh]

The final invocation of proveVoteTallyBatch() requires that the sender pass in a uint256[] memory _finalResults value. There is be an upper limit on the size of the array (a simple test showed that the limit is between 2 ** 5 and 2 ** 6 values), and make it impossible to tally the final batch.

I have a workaround in mind but I will think of more solutions:

Create a function which accepts a batch of values from the full list of results, and inserts each value into a Merkle tree, and store the root on-chain. One transaction is required per batch. Once all batches have been inserted, the final invocation of proveVoteTallyBatch() can look up the root and use it to verify that the commitment to the final tally is correct. Doing so will, however, reveal the results before the final invocation of proveVoteTallyBatch().

Edit (3 May 2020): After discussing with @kobigurk, I've created issue #91 and will close this issue in favour of it.