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Added backward skip list

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Vitalik Buterin 2018-10-02 14:13:13 -04:00
parent 95b67a4fd0
commit 894fb380f3
1 changed files with 15 additions and 6 deletions
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specs/casper_sharding_v2.1.md
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@ -68,8 +68,8 @@ Beacon chain block structure:
```python ```python
fields = { fields = {
# Hash of the parent block # Hash of ancestor blocks (32 items, i'th is 2**i'th ancestor or zero bytes)
'parent_hash': 'hash32', 'ancestor_hashes': ['hash32'],
# Slot number (for the PoS mechanism) # Slot number (for the PoS mechanism)
'slot': 'int64', 'slot': 'int64',
# Randao commitment reveal # Randao commitment reveal
@ -225,7 +225,7 @@ Processing the beacon chain is fundamentally similar to processing a PoW chain i
For a block on the beacon chain to be processed by a node, four conditions have to be met: For a block on the beacon chain to be processed by a node, four conditions have to be met:
* The parent pointed to by the `parent_hash` has already been processed and accepted * The parent pointed to by the `ancestor_hashes[0]` has already been processed and accepted
* An attestation from the _proposer_ of the block (see later for definition) is included along with the block in the network message object * An attestation from the _proposer_ of the block (see later for definition) is included along with the block in the network message object
* The PoW chain block pointed to by the `pow_chain_ref` has already been processed and accepted * The PoW chain block pointed to by the `pow_chain_ref` has already been processed and accepted
* The node's local clock time is greater than or equal to the minimum timestamp as computed by `GENESIS_TIME + block.slot * SLOT_DURATION` * The node's local clock time is greater than or equal to the minimum timestamp as computed by `GENESIS_TIME + block.slot * SLOT_DURATION`
@ -418,7 +418,7 @@ def add_validator(validators, pubkey, proof_of_possession, withdrawal_shard,
This procedure should be carried out every block. This procedure should be carried out every block.
First, set `recent_block_hashes` to the output of the following: First, set `recent_block_hashes` to the output of the following, where `parent_hash` is the hash of the immediate previous block (ie. must be equal to `ancestor_hashes[0]`):
```python ```python
def get_new_recent_block_hashes(old_block_hashes, parent_slot, def get_new_recent_block_hashes(old_block_hashes, parent_slot,
@ -427,7 +427,16 @@ def get_new_recent_block_hashes(old_block_hashes, parent_slot,
return old_block_hashes[d:] + [parent_hash] * min(d, len(old_block_hashes)) return old_block_hashes[d:] + [parent_hash] * min(d, len(old_block_hashes))
``` ```
The output of `get_block_hash` should not change, except that it will no longer throw for `current_slot - 1`, and will now throw for `current_slot - CYCLE_LENGTH * 2 - 1` The output of `get_block_hash` should not change, except that it will no longer throw for `current_slot - 1`, and will now throw for `current_slot - CYCLE_LENGTH * 2 - 1`. Also, check that the block's `ancestor_hashes` array was correctly updated, using the following algorithm:
```python
def update_ancestor_hashes(parent_ancestor_hashes, parent_slot_number, parent_hash):
new_ancestor_hashes = copy.copy(parent_ancestor_hashes)
for i in range(32):
if parent_slot_number % 2**i == 0:
new_ancestor_hashes[i] = parent_hash
return new_ancestor_hashes
```
A block can have 0 or more `AttestationRecord` objects A block can have 0 or more `AttestationRecord` objects
@ -563,7 +572,7 @@ Finally:
* Set `last_dynasty_start = crystallized_state.last_state_recalculation` * Set `last_dynasty_start = crystallized_state.last_state_recalculation`
* Set `crystallized_state.current_dynasty += 1` * Set `crystallized_state.current_dynasty += 1`
* Let `next_start_shard = (shard_and_committee_for_slots[-1][-1].shard_id + 1) % SHARD_COUNT` * Let `next_start_shard = (shard_and_committee_for_slots[-1][-1].shard_id + 1) % SHARD_COUNT`
* Set `shard_and_committee_for_slots[CYCLE_LENGTH:] = get_new_shuffling(block.parent_hash, validators, next_start_shard)` * Set `shard_and_committee_for_slots[CYCLE_LENGTH:] = get_new_shuffling(block.ancestor_hashes[0], validators, next_start_shard)`
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