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Strict ValidatorIndex definition #1714

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merged 2 commits into from
Apr 14, 2020
Merged

Strict ValidatorIndex definition #1714

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890c27d
The input parameter `index` in `compute_shuffled_index` is the positi…
hwwhww Apr 9, 2020
b2f6325
Fix `compute_committee`
hwwhww Apr 9, 2020
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14 changes: 7 additions & 7 deletions specs/phase0/beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -722,24 +722,24 @@ def is_valid_merkle_branch(leaf: Bytes32, branch: Sequence[Bytes32], depth: uint
#### `compute_shuffled_index`

```python
def compute_shuffled_index(index: ValidatorIndex, index_count: uint64, seed: Bytes32) -> ValidatorIndex:
def compute_shuffled_index(index: uint64, index_count: uint64, seed: Bytes32) -> uint64:
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Maybe the input param should be renamed offset as further differentiation?

"""
Return the shuffled validator index corresponding to ``seed`` (and ``index_count``).
Return the shuffled index corresponding to ``seed`` (and ``index_count``).
"""
assert index < index_count

# Swap or not (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
# See the 'generalized domain' algorithm on page 3
for current_round in range(SHUFFLE_ROUND_COUNT):
pivot = bytes_to_int(hash(seed + int_to_bytes(current_round, length=1))[0:8]) % index_count
flip = ValidatorIndex((pivot + index_count - index) % index_count)
flip = (pivot + index_count - index) % index_count
position = max(index, flip)
source = hash(seed + int_to_bytes(current_round, length=1) + int_to_bytes(position // 256, length=4))
byte = source[(position % 256) // 8]
bit = (byte >> (position % 8)) % 2
index = flip if bit else index

return ValidatorIndex(index)
return index
```

#### `compute_proposer_index`
Expand All @@ -753,11 +753,11 @@ def compute_proposer_index(state: BeaconState, indices: Sequence[ValidatorIndex]
MAX_RANDOM_BYTE = 2**8 - 1
i = 0
while True:
candidate_index = indices[compute_shuffled_index(ValidatorIndex(i % len(indices)), len(indices), seed)]
candidate_index = indices[compute_shuffled_index(i % len(indices), len(indices), seed)]
random_byte = hash(seed + int_to_bytes(i // 32, length=8))[i % 32]
effective_balance = state.validators[candidate_index].effective_balance
if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
return ValidatorIndex(candidate_index)
return candidate_index
i += 1
```

Expand All @@ -773,7 +773,7 @@ def compute_committee(indices: Sequence[ValidatorIndex],
"""
start = (len(indices) * index) // count
end = (len(indices) * (index + 1)) // count
return [indices[compute_shuffled_index(ValidatorIndex(i), len(indices), seed)] for i in range(start, end)]
return [indices[compute_shuffled_index(i, len(indices), seed)] for i in range(start, end)]
```

#### `compute_epoch_at_slot`
Expand Down