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Fix #1090 #1092

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merged 3 commits into from
May 17, 2019
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Fix #1090 #1092

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05f9dc7
Fix #1090
JustinDrake May 17, 2019
f191888
Update 0_beacon-chain.md
JustinDrake May 17, 2019
694b31b
Update 0_beacon-chain.md
JustinDrake May 17, 2019
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12 changes: 6 additions & 6 deletions specs/core/0_beacon-chain.md
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Original file line number Diff line number Diff line change
Expand Up @@ -647,7 +647,7 @@ def get_previous_epoch(state: BeaconState) -> Epoch:
Return the current epoch if it's genesis epoch.
"""
current_epoch = get_current_epoch(state)
return (current_epoch - 1) if current_epoch > GENESIS_EPOCH else current_epoch
return GENESIS_EPOCH if current_epoch == GENESIS_EPOCH else current_epoch - 1
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Tiny tiny nitpick: the previous version looks fine to me, and slightly more efficient since we expect in most cases, current_epoch is greater than GENESIS_EPOCH.

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I was trying to make it clear that current_epoch - 1 is not even "considered" unless current_epoch != GENESIS. Not too fussed either way :)

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So in python, the left side is never run if the conditional is False, but I think this makes it slightly clearer to be careful with the subtraction. I'm oky with as is

```

### `get_current_epoch`
Expand Down Expand Up @@ -887,7 +887,7 @@ def get_shuffled_index(index: ValidatorIndex, index_count: int, seed: Bytes32) -
# See the 'generalized domain' algorithm on page 3
for round in range(SHUFFLE_ROUND_COUNT):
pivot = bytes_to_int(hash(seed + int_to_bytes(round, length=1))[0:8]) % index_count
flip = (pivot - index) % index_count
flip = (pivot + index_count - index) % index_count
position = max(index, flip)
source = hash(seed + int_to_bytes(round, length=1) + int_to_bytes(position // 256, length=4))
byte = source[(position % 256) // 8]
Expand Down Expand Up @@ -1362,19 +1362,19 @@ def process_justification_and_finalization(state: BeaconState) -> None:
# Process finalizations
bitfield = state.justification_bitfield
# The 2nd/3rd/4th most recent epochs are justified, the 2nd using the 4th as source
if (bitfield >> 1) % 8 == 0b111 and old_previous_justified_epoch == current_epoch - 3:
if (bitfield >> 1) % 8 == 0b111 and old_previous_justified_epoch + 3 == current_epoch:
state.finalized_epoch = old_previous_justified_epoch
state.finalized_root = get_block_root(state, state.finalized_epoch)
# The 2nd/3rd most recent epochs are justified, the 2nd using the 3rd as source
if (bitfield >> 1) % 4 == 0b11 and old_previous_justified_epoch == current_epoch - 2:
if (bitfield >> 1) % 4 == 0b11 and old_previous_justified_epoch + 2 == current_epoch:
state.finalized_epoch = old_previous_justified_epoch
state.finalized_root = get_block_root(state, state.finalized_epoch)
# The 1st/2nd/3rd most recent epochs are justified, the 1st using the 3rd as source
if (bitfield >> 0) % 8 == 0b111 and old_current_justified_epoch == current_epoch - 2:
if (bitfield >> 0) % 8 == 0b111 and old_current_justified_epoch + 2 == current_epoch:
state.finalized_epoch = old_current_justified_epoch
state.finalized_root = get_block_root(state, state.finalized_epoch)
# The 1st/2nd most recent epochs are justified, the 1st using the 2nd as source
if (bitfield >> 0) % 4 == 0b11 and old_current_justified_epoch == current_epoch - 1:
if (bitfield >> 0) % 4 == 0b11 and old_current_justified_epoch + 1 == current_epoch:
state.finalized_epoch = old_current_justified_epoch
state.finalized_root = get_block_root(state, state.finalized_epoch)
```
Expand Down