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49 lines
1.7 KiB
Go
49 lines
1.7 KiB
Go
// Package utils defines utility functions for the beacon-chain.
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package utils
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import (
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"errors"
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"github.com/ethereum/go-ethereum/common"
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"github.com/prysmaticlabs/prysm/beacon-chain/params"
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"github.com/prysmaticlabs/prysm/shared/hashutil"
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)
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// ShuffleIndices returns a list of pseudorandomly sampled
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// indices. This is used to use to select attesters and proposers.
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func ShuffleIndices(seed common.Hash, validatorList []uint32) ([]uint32, error) {
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// Since we are consuming 3 bytes of entropy at a time in the loop,
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// we have a bias at 2**24, this check defines our max list size and is used to remove the bias.
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// more info on modulo bias: https://stackoverflow.com/questions/10984974/why-do-people-say-there-is-modulo-bias-when-using-a-random-number-generator.
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if len(validatorList) > params.GetConfig().ModuloBias {
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return nil, errors.New("exceeded upper bound for validator shuffle")
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}
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hashSeed := hashutil.Hash(seed[:])
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validatorCount := len(validatorList)
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// Shuffle stops at the second to last index.
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for i := 0; i < validatorCount-1; i++ {
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// Convert every 3 bytes to random number, replace validator index with that number.
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for j := 0; j+3 < len(hashSeed); j += 3 {
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swapNum := int(hashSeed[j] + hashSeed[j+1] + hashSeed[j+2])
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remaining := validatorCount - i
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swapPos := swapNum%remaining + i
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validatorList[i], validatorList[swapPos] = validatorList[swapPos], validatorList[i]
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}
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hashSeed = hashutil.Hash(seed[:])
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}
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return validatorList, nil
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}
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// SplitIndices splits a list into n pieces.
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func SplitIndices(l []uint32, n int) [][]uint32 {
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var divided [][]uint32
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for i := 0; i < n; i++ {
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start := len(l) * i / n
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end := len(l) * (i + 1) / n
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divided = append(divided, l[start:end])
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}
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return divided
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}
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