EIP-150 fork oracle.

AmIOnEIP150Fork.sol

pragma solidity ^0.4.2;

contract AmIOnEIP150Fork {
    // Tracks whether or not hard fork is effective on this chain.
    bool public forked = false;
    // Event emitted on updates during fork window to indicate status.
    event ForkedStatus(bool forked);

    // This function should be called between block X and Y.
    function update() {
        if (block.number >= 2463000 && block.number <= 2464200) {
            uint beforeGas = 0;
            uint afterGas = 0;
            assembly {
                beforeGas := gas
                balance
                afterGas := gas
            }
            
            // Check if gas cost of sequence of instructions above has changed
            // from pre-fork constant amount. The constant 27 results from the
            // following sequence of instructions encoded in assembly block
            // after the first GAS opcode call:
            //
            // 1 SWAP2 + 1 POP + 1 BALANCE + 1 GAS
            //   = 3 gas (SWAP2) + 2 gas (POP) + 20 gas (BALANCE) + 2 gas (GAS)
            //   = 3 gas + 2 gas + 20 gas + 2 gas
            //   = 27 gas
            //
            forked = ((beforeGas - afterGas) != 27);
            ForkedStatus(forked);
        }
    }
}

I think the forked variable should have 3 states: not yet determined, forked, or unforked.

The fallback function is throw by default now I think in Solidity >= 4.0.

Maybe put a log in when update determines the fork?

@jimpo The tri-partite forked state doesn't make sense to me, but I may be missing something. To my mind it is a boolean, either the chain you are on is the forked chain or it is not.

yeah - prior to the fork point, it is reasonable to declare it unforked.

@etscrivner did you end up deploying this contract?