This code determines the order in which the next branch element and the
current value should be hashed to produce the parent node in the Merkle tree.
The existing code fails to verify branches constructed in the standard way.
This patch fixes the spec code so that it works properly by using an appropriate
parity calculation.
Example code here to illustrate it working:
https://gist.github.com/ralexstokes/9d82e188bd3286ff74a1fa1dcb5068e0
`EJECTION_BALANCE` is in units of ETH.
`state.validator_balances[index]` is in units of Gwei.
For the ejection computation to work as desired, we need to convert the
`EJECTION_BALANCE` constant from ETH to Gwei.
There should be a correspondence here but referring to the slot is more
explicit, especially for those who are not as familiar with the
details of FFG finalization.
* Cleanup comments related to custody
* Rename "Miscellaneous" to "Custody" in the table of contents
* Use `INITIAL_SLOT_NUMBER` instead of `0` for initial custody slots
* (typo) Fix `second_latest_custody_reseed_slot` => `penultimate_custody_reseed_slot`
Added `latest_vdf_outputs` in `state` initialised to an array of `ZERO_HASH` of length `LATEST_RANDAO_MIXES_LENGTH // EPOCH_LENGTH`. (There's one VDF output per epoch. The VDF input is the RANDAO mix at the epoch boundary.)
Further changes to activate VDFs (in a future phase):
* Add a new beacon "VDF output and proof" transaction, e.g. with `MAX_VDF_OUTPUT_AND_PROOF := 1`.
* Adjust the `MAX_SEED_LOOKAHEAD` constant, e.g. to `2**4 * EPOCH_LENGTH`. (The `2**4` parameter is essentially `A_max`.)
* Add a `process_vdf_output_and_proof` helper function in the per-block processing:
* Verify the VDF input hasn't already been processed (check the corresponding `state.latest_vdf_outputs` entry is not `ZERO_HASH`.)
* Verify the proof is correct, i.e. matches the VDF input and output
* Save the VDF output to `state.latest_vdf_outputs`
* In the per-epoch processing set the corresponding entry in `state.latest_vdf_outputs` to `ZERO_HASH`.
* Use a VDF output for the shuffling seed.
