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Make use of object initial values #843

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Make use of object initial values #843

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6cebfa3
Make use of object initial values
JustinDrake Mar 26, 2019
208bc88
Update 0_beacon-chain.md
JustinDrake Mar 26, 2019
6393eba
Update 0_beacon-chain.md
JustinDrake Mar 28, 2019
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106 changes: 7 additions & 99 deletions specs/core/0_beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,6 @@
- [`hash`](#hash)
- [`hash_tree_root`](#hash_tree_root)
- [`signed_root`](#signed_root)
- [`get_temporary_block_header`](#get_temporary_block_header)
- [`slot_to_epoch`](#slot_to_epoch)
- [`get_previous_epoch`](#get_previous_epoch)
- [`get_current_epoch`](#get_current_epoch)
Expand Down Expand Up @@ -209,13 +208,10 @@ Code snippets appearing in `this style` are to be interpreted as Python code.

| Name | Value |
| - | - |
| `GENESIS_FORK_VERSION` | `int_to_bytes4(0)` |
| `GENESIS_SLOT` | `2**32` |
| `GENESIS_EPOCH` | `slot_to_epoch(GENESIS_SLOT)` |
| `GENESIS_START_SHARD` | `0` |
| `FAR_FUTURE_EPOCH` | `2**64 - 1` |
| `ZERO_HASH` | `int_to_bytes32(0)` |
| `EMPTY_SIGNATURE` | `int_to_bytes96(0)` |
| `BLS_WITHDRAWAL_PREFIX_BYTE` | `int_to_bytes1(0)` |

* `GENESIS_SLOT` should be at least as large in terms of time as the largest of the time parameters or state list lengths below (ie. it should be at least as large as any value measured in slots, and at least `SLOTS_PER_EPOCH` times as large as any value measured in epochs).
Expand Down Expand Up @@ -259,7 +255,6 @@ Code snippets appearing in `this style` are to be interpreted as Python code.
* The `BASE_REWARD_QUOTIENT` parameter dictates the per-epoch reward. It corresponds to ~2.54% annual interest assuming 10 million participating ETH in every epoch.
* The `INACTIVITY_PENALTY_QUOTIENT` equals `INVERSE_SQRT_E_DROP_TIME**2` where `INVERSE_SQRT_E_DROP_TIME := 2**12 epochs` (~18 days) is the time it takes the inactivity penalty to reduce the balance of non-participating [validators](#dfn-validator) to about `1/sqrt(e) ~= 60.6%`. Indeed, the balance retained by offline [validators](#dfn-validator) after `n` epochs is about `(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(n**2/2)` so after `INVERSE_SQRT_E_DROP_TIME` epochs it is roughly `(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(INACTIVITY_PENALTY_QUOTIENT/2) ~= 1/sqrt(e)`.


### Max transactions per block

| Name | Value |
Expand Down Expand Up @@ -664,23 +659,6 @@ Note: We aim to migrate to a S[T/N]ARK-friendly hash function in a future Ethere

`def signed_root(object: SSZContainer) -> Bytes32` is a function defined in the [SimpleSerialize spec](https://github.com/ethereum/eth2.0-specs/blob/master/specs/simple-serialize.md#signed-roots) to compute signed messages.

### `get_temporary_block_header`

```python
def get_temporary_block_header(block: BeaconBlock) -> BeaconBlockHeader:
"""
Return the block header corresponding to a block with ``state_root`` set to ``ZERO_HASH``.
"""
return BeaconBlockHeader(
slot=block.slot,
previous_block_root=block.previous_block_root,
state_root=ZERO_HASH,
block_body_root=hash_tree_root(block.body),
# signed_root(block) is used for block id purposes so signature is a stub
signature=EMPTY_SIGNATURE,
)
```

### `slot_to_epoch`

```python
Expand Down Expand Up @@ -1311,9 +1289,6 @@ def process_deposit(state: BeaconState, deposit: Deposit) -> None:
activation_epoch=FAR_FUTURE_EPOCH,
exit_epoch=FAR_FUTURE_EPOCH,
withdrawable_epoch=FAR_FUTURE_EPOCH,
initiated_exit=False,
slashed=False,
high_balance=0
)

# Note: In phase 2 registry indices that have been withdrawn for a long time will be recycled.
Expand Down Expand Up @@ -1457,35 +1432,7 @@ When enough full deposits have been made to the deposit contract, an `Eth2Genesi
* `genesis_eth1_data.deposit_count` is the `deposit_count` contained in the `Eth2Genesis` log.
* `genesis_eth1_data.block_hash` is the hash of the Ethereum 1.0 block that emitted the `Eth2Genesis` log.
* Let `genesis_state = get_genesis_beacon_state(genesis_validator_deposits, genesis_time, genesis_eth1_data)`.
* Let `genesis_block = get_empty_block()`.
* Set `genesis_block.state_root = hash_tree_root(genesis_state)`.

```python
def get_empty_block() -> BeaconBlock:
"""
Get an empty ``BeaconBlock``.
"""
return BeaconBlock(
slot=GENESIS_SLOT,
previous_block_root=ZERO_HASH,
state_root=ZERO_HASH,
body=BeaconBlockBody(
randao_reveal=EMPTY_SIGNATURE,
eth1_data=Eth1Data(
deposit_root=ZERO_HASH,
deposit_count=0,
block_hash=ZERO_HASH,
),
proposer_slashings=[],
attester_slashings=[],
attestations=[],
deposits=[],
voluntary_exits=[],
transfers=[],
),
signature=EMPTY_SIGNATURE,
)
```
* Let `genesis_block = BeaconBlock(state_root=hash_tree_root(genesis_state))`.

```python
def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
Expand All @@ -1494,50 +1441,7 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
"""
Get the genesis ``BeaconState``.
"""
state = BeaconState(
# Misc
slot=GENESIS_SLOT,
genesis_time=genesis_time,
fork=Fork(
previous_version=GENESIS_FORK_VERSION,
current_version=GENESIS_FORK_VERSION,
epoch=GENESIS_EPOCH,
),

# Validator registry
validator_registry=[],
balances=[],
validator_registry_update_epoch=GENESIS_EPOCH,

# Randomness and committees
latest_randao_mixes=Vector([ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH)]),
latest_start_shard=GENESIS_START_SHARD,

# Finality
previous_epoch_attestations=[],
current_epoch_attestations=[],
previous_justified_epoch=GENESIS_EPOCH - 1,
current_justified_epoch=GENESIS_EPOCH,
previous_justified_root=ZERO_HASH,
current_justified_root=ZERO_HASH,
justification_bitfield=0,
finalized_epoch=GENESIS_EPOCH,
finalized_root=ZERO_HASH,

# Recent state
latest_crosslinks=Vector([Crosslink(epoch=GENESIS_EPOCH, crosslink_data_root=ZERO_HASH) for _ in range(SHARD_COUNT)]),
latest_block_roots=Vector([ZERO_HASH for _ in range(SLOTS_PER_HISTORICAL_ROOT)]),
latest_state_roots=Vector([ZERO_HASH for _ in range(SLOTS_PER_HISTORICAL_ROOT)]),
latest_active_index_roots=Vector([ZERO_HASH for _ in range(LATEST_ACTIVE_INDEX_ROOTS_LENGTH)]),
latest_slashed_balances=Vector([0 for _ in range(LATEST_SLASHED_EXIT_LENGTH)]),
latest_block_header=get_temporary_block_header(get_empty_block()),
historical_roots=[],

# Ethereum 1.0 chain data
latest_eth1_data=genesis_eth1_data,
eth1_data_votes=[],
deposit_index=0,
)
state = BeaconState(genesis_time=genesis_time, latest_eth1_data=genesis_eth1_data)

# Process genesis deposits
for deposit in genesis_validator_deposits:
Expand Down Expand Up @@ -2160,7 +2064,11 @@ def process_block_header(state: BeaconState, block: BeaconBlock) -> None:
# Verify that the parent matches
assert block.previous_block_root == signed_root(state.latest_block_header)
# Save current block as the new latest block
state.latest_block_header = get_temporary_block_header(block)
state.latest_block_header = BeaconBlockHeader(
slot=block.slot,
previous_block_root=block.previous_block_root,
block_body_root=hash_tree_root(block.body),
)
# Verify proposer is not slashed
proposer = state.validator_registry[get_beacon_proposer_index(state, state.slot)]
assert not proposer.slashed
Expand Down