# beacon_chain # Copyright (c) 2018 Status Research & Development GmbH # Licensed and distributed under either of # * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT). # * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0). # at your option. This file may not be copied, modified, or distributed except according to those terms. # Uncategorized helper functions from the spec import ./datatypes, ./digest, sequtils, math func shuffle*[T](values: seq[T], seed: Eth2Digest): seq[T] = ## Returns the shuffled ``values`` with seed as entropy. ## TODO: this calls out for tests, but I odn't particularly trust spec ## right now. let values_count = values.len const # Entropy is consumed from the seed in 3-byte (24 bit) chunks. rand_bytes = 3 # The highest possible result of the RNG. rand_max = 2^(rand_bytes * 8) - 1 # The range of the RNG places an upper-bound on the size of the list that # may be shuffled. It is a logic error to supply an oversized list. assert values_count < rand_max result = values var source = seed index = 0 while index < values_count - 1: # Re-hash the `source` to obtain a new pattern of bytes. source = eth2hash source.data # Iterate through the `source` bytes in 3-byte chunks. for pos in countup(0, 29, 3): let remaining = values_count - index if remaining == 1: break # Read 3-bytes of `source` as a 24-bit big-endian integer. let sample_from_source = source.data[pos].Uint24 shl 16 or source.data[pos+1].Uint24 shl 8 or source.data[pos+2].Uint24 # Sample values greater than or equal to `sample_max` will cause # modulo bias when mapped into the `remaining` range. let sample_max = rand_max - rand_max mod remaining # Perform a swap if the consumed entropy will not cause modulo bias. if sample_from_source < sample_max: # Select a replacement index for the current index. let replacement_position = sample_from_source mod remaining + index swap result[index], result[replacement_position] inc index func split*[T](lst: openArray[T], N: Positive): seq[seq[T]] = ## split lst in N pieces, with each piece having `len(lst) div N` or ## `len(lst) div N + 1` pieces # TODO: implement as an iterator result = newSeq[seq[T]](N) for i in 0 ..< N: result[i] = lst[lst.len * i div N ..< lst.len * (i+1) div N] # TODO: avoid alloc via toOpenArray func get_new_recent_block_hashes*(old_block_hashes: seq[Eth2Digest], parent_slot, current_slot: int64, parent_hash: Eth2Digest ): seq[Eth2Digest] = # Should throw for `current_slot - CYCLE_LENGTH * 2 - 1` according to spec comment let d = current_slot - parent_slot result = old_block_hashes[d .. ^1] for _ in 0 ..< min(d, old_block_hashes.len): result.add parent_hash func ceil_div8*(v: int): int = (v + 7) div 8 # TODO use a proper bitarray! func repeat_hash*(v: Eth2Digest, n: SomeInteger): Eth2Digest = if n == 0: v else: repeat_hash(eth2hash(v.data), n - 1)