VMC Optimization

[hwwhww]

Thanks to @vbuterin for providing some suggestions.

Goal

Get down to ~90-100k gas in practice without too much effort

Items

• [x] Storing score and parent inside a single storage key
  • giving collations a 24 byte ID instead of 32 byte: ID = num256_add(shift(parent, -192), num256_and(sha3(header), as_num256(<valueof 2**192 - 1 here>)))
• [x] Using emitting log instead of storing collations_with_score mapping
• [x] Remove validator code, just use the signature of the transaction itself.
  • Record the address of validator in validators mapping and remove validator_code_addr:

    validators: public({
        # Amount of wei the validator holds
        deposit: wei_value,
        # The address which the validator
        validation_addr: address,
        # Addess to withdraw to
        return_addr: address,
        # The cycle number which the validator would be included after
        # Will be [DEPRECATED] for stateless client
        cycle: num,
    }[num])

  • Make get_eligible_proposer return validator_addr
  • Change the input of add_header by removing sig field: add_header(shard_id: num, expected_period_number: num, period_start_prevhash: bytes32, parent_collation_hash: bytes32, tx_list_root: bytes32, collation_coinbase: address, post_state_root: bytes32, receipt_root: bytes32, collation_number: num)
  • [in add_header] assert msg.sender == self.get_eligible_proposer(shard_id, block.number / self.period_length)
  • Remove the RLP decoding and update entire_header_hash: entire_header_hash = sha3(concat(as_bytes32(shard_id), as_bytes32(expected_period_number) ... as_bytes32(collation_number)))
  • [in withdraw] assert msg.sender == self.validators[validator_index].validator_addr

[mhchia]

Link to collation header optimisation

[hwwhww]

yay! this issue is done.