This is a new implementation of the incremental merkle tree used by our
scheme to witness commitments to spendable value. It serves as a fixed-sized
accumulator.
This new construction has a much simpler API surface area, avoids memory
safety issues, remains pruned at all times, avoids serialization edge cases,
has more efficient insertion, and is abstract over the depth and hash
function used at the type level.
Further, it lays the groundwork for efficient "fast-forwarding" of witnesses
into the tree as the treestate is updated.
After a new block is found or after a few nonces have been tried (currently
after every nonce), the miner checks for global changes. If any of these are
triggered, a new block is built from scratch, which re-initialises the Equihash
input. But if none of the checks are triggered, the miner just updates nTime and
continues mining - without updating the Equihash input to account for the new
block header. This bugfix corrects the behaviour by regenerating the Equihash
input in both situations.
All blocks before the first subsidy halving block, with the exception of
the genesis block, must contain an output which sends 20% of the block
subsidy value to a scriptPubKey `FOUNDERS_REWARD_SCRIPT`.
Changing the order of difficulty calculation operations to divide first doesn't
affect the result significantly, but ensures we never overflow the arith_uint256
during multiplication and get an artificial jump in difficulty.
Changes to bloom tests were done by running the following commands:
sed -i 's/\(CDataStream stream(ParseHex(".\{152\}\)\(.\{8\}\)/\100000000000000000000000000000000000000000000000000000000\200/' src/test/bloom_tests.cpp
sed -i 's/\(vector<unsigned char> vch = ParseHex(".\{152\}\)\(.\{8\}\)/\100000000000000000000000000000000000000000000000000000000\200/' src/test/bloom_tests.cpp
and then reverting the single change to the transaction line.
The main and test networks are configured to use parameters that are currently
low-memory but usable with the basic solver; they will be increased once the
solver is optimised. The regtest network is configured to have extremely low
memory usage for speed.
Note that Bitcoin's double-hasher is used for the difficulty check. This does
not match the paper, but is simpler than changing the block header
serialization. Single hashing is kept for the EquiHash solver because there is
no requirement on execution time there, only on memory usage.
Sean Bowe