2018-07-23 12:58:41 +00:00
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# beacon_chain
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# Copyright (c) 2018 Status Research & Development GmbH
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# Licensed and distributed under either of
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# * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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2018-11-28 19:49:03 +00:00
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# Uncategorized helper functions from the spec
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import ./datatypes, ./digest, sequtils, math
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2018-07-23 12:58:41 +00:00
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2018-12-03 21:41:24 +00:00
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func mod_get[T](arr: openarray[T], pos: Natural): T =
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arr[pos mod arr.len]
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2018-11-27 23:10:09 +00:00
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func shuffle*[T](values: seq[T], seed: Eth2Digest): seq[T] =
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2018-11-16 00:54:36 +00:00
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## Returns the shuffled ``values`` with seed as entropy.
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## TODO: this calls out for tests, but I odn't particularly trust spec
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## right now.
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2018-07-23 12:58:41 +00:00
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2018-11-16 00:54:36 +00:00
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let values_count = values.len
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2018-07-23 12:58:41 +00:00
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2018-11-23 19:42:47 +00:00
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const
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# Entropy is consumed from the seed in 3-byte (24 bit) chunks.
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rand_bytes = 3
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# The highest possible result of the RNG.
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rand_max = 2^(rand_bytes * 8) - 1
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2018-11-16 00:54:36 +00:00
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# The range of the RNG places an upper-bound on the size of the list that
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# may be shuffled. It is a logic error to supply an oversized list.
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assert values_count < rand_max
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2018-11-23 19:42:47 +00:00
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result = values
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var
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source = seed
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index = 0
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while index < values_count - 1:
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# Re-hash the `source` to obtain a new pattern of bytes.
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2018-11-27 23:10:09 +00:00
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source = eth2hash source.data
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2018-11-23 22:44:43 +00:00
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2018-11-23 19:42:47 +00:00
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# Iterate through the `source` bytes in 3-byte chunks.
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2018-07-23 12:58:41 +00:00
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for pos in countup(0, 29, 3):
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2018-11-23 19:42:47 +00:00
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let remaining = values_count - index
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2018-11-16 00:54:36 +00:00
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if remaining == 1:
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2018-07-23 12:58:41 +00:00
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break
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2018-11-16 00:54:36 +00:00
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# Read 3-bytes of `source` as a 24-bit big-endian integer.
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2018-11-23 19:42:47 +00:00
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let sample_from_source =
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source.data[pos].Uint24 shl 16 or
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source.data[pos+1].Uint24 shl 8 or
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source.data[pos+2].Uint24
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2018-07-23 12:58:41 +00:00
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2018-11-16 00:54:36 +00:00
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# Sample values greater than or equal to `sample_max` will cause
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# modulo bias when mapped into the `remaining` range.
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let sample_max = rand_max - rand_max mod remaining
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# Perform a swap if the consumed entropy will not cause modulo bias.
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if sample_from_source < sample_max:
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2018-11-23 19:42:47 +00:00
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# Select a replacement index for the current index.
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let replacement_position = sample_from_source mod remaining + index
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swap result[index], result[replacement_position]
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inc index
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2018-07-23 14:22:37 +00:00
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2018-11-23 19:42:47 +00:00
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func split*[T](lst: openArray[T], N: Positive): seq[seq[T]] =
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2018-11-23 22:44:43 +00:00
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## split lst in N pieces, with each piece having `len(lst) div N` or
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## `len(lst) div N + 1` pieces
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2018-08-17 16:21:25 +00:00
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# TODO: implement as an iterator
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result = newSeq[seq[T]](N)
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for i in 0 ..< N:
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result[i] = lst[lst.len * i div N ..< lst.len * (i+1) div N] # TODO: avoid alloc via toOpenArray
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2018-11-27 23:10:09 +00:00
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func get_new_recent_block_hashes*(old_block_hashes: seq[Eth2Digest],
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2018-11-23 19:42:47 +00:00
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parent_slot, current_slot: int64,
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2018-11-27 23:10:09 +00:00
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parent_hash: Eth2Digest
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): seq[Eth2Digest] =
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2018-08-21 16:21:45 +00:00
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# Should throw for `current_slot - CYCLE_LENGTH * 2 - 1` according to spec comment
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let d = current_slot - parent_slot
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result = old_block_hashes[d .. ^1]
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for _ in 0 ..< min(d, old_block_hashes.len):
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result.add parent_hash
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2018-11-29 22:11:05 +00:00
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func ceil_div8*(v: int): int = (v + 7) div 8 # TODO use a proper bitarray!
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func repeat_hash*(v: Eth2Digest, n: SomeInteger): Eth2Digest =
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if n == 0:
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v
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else:
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repeat_hash(eth2hash(v.data), n - 1)
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2018-12-03 21:41:24 +00:00
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func get_shard_and_committees_index*(state: BeaconState, slot: uint64): uint64 =
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# TODO spec unsigned-unsafe here
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let earliest_slot_in_array =
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if state.latest_state_recalculation_slot > EPOCH_LENGTH.uint64:
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state.latest_state_recalculation_slot - EPOCH_LENGTH
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else:
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0
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doAssert earliest_slot_in_array <= slot and
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slot < earliest_slot_in_array + EPOCH_LENGTH * 2
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slot - earliest_slot_in_array
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proc get_shard_and_committees_for_slot*(
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state: BeaconState, slot: uint64): seq[ShardAndCommittee] =
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let index = state.get_shard_and_committees_index(slot)
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state.shard_and_committee_for_slots[index]
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2018-12-04 18:45:30 +00:00
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func get_beacon_proposer_index*(state: BeaconState, slot: uint64): Uint24 =
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2018-12-03 21:41:24 +00:00
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## From Casper RPJ mini-spec:
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## When slot i begins, validator Vidx is expected
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## to create ("propose") a block, which contains a pointer to some parent block
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## that they perceive as the "head of the chain",
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## and includes all of the **attestations** that they know about
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## that have not yet been included into that chain.
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##
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## idx in Vidx == p(i mod N), pi being a random permutation of validators indices (i.e. a committee)
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let idx = get_shard_and_committees_index(state, slot)
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state.shard_and_committee_for_slots[idx][0].committee.mod_get(slot)
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func int_sqrt*(n: SomeInteger): SomeInteger =
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var
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x = n
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y = (x + 1) div 2
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while y < x:
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x = y
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y = (x + n div x) div 2
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x
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func get_fork_version*(fork_data: ForkData, slot: uint64): uint64 =
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if slot < fork_data.fork_slot: fork_data.pre_fork_version
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else: fork_data.post_fork_version
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func get_domain*(fork_data: ForkData, slot: uint64, domain_type: uint64): uint64 =
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# TODO Slot overflow? Or is slot 32 bits for all intents and purposes?
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(get_fork_version(fork_data, slot) shl 32) + domain_type
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2018-12-04 18:45:30 +00:00
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2018-12-05 13:07:42 +00:00
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func is_power_of_2*(v: uint64): bool = (v and (v-1)) == 0
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