34 lines
1.2 KiB
Nim
34 lines
1.2 KiB
Nim
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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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# Helper functions
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import ../datatypes, sequtils, nimcrypto
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func getShuffling(seed: Blake2_256_Digest, validatorCount: int): seq[int] {.noInit.}=
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# Pseudorandomly shuffles the validator set based on some seed
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assert validatorCount <= MaxValidatorCount
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let randMax = MaxValidatorCount - MaxValidatorCount mod validatorCount
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result = toSeq(0 ..< validatorCount)
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var source = seed
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var i = 0
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while i < validatorCount:
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source = blake2_256.digest source.data
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for pos in countup(0, 29, 3):
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let remaining = validatorCount - i
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if remaining == 0:
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break
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let m = source.data[pos].int shl 16 or source.data[pos+1].int shl 8 or source.data[pos+2].int
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if validatorCount < randMax:
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let replacementPos = m mod remaining + i
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swap result[i], result[replacementPos]
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inc i
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