mirror of
https://github.com/status-im/nim-codex.git
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76 lines
2.0 KiB
Nim
76 lines
2.0 KiB
Nim
## Nim-Codex
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## Copyright (c) 2024 Status Research & Development GmbH
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## Licensed under either of
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## * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
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## * MIT license ([LICENSE-MIT](LICENSE-MIT))
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## at your option.
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## This file may not be copied, modified, or distributed except according to
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## those terms.
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import std/bitops
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import pkg/questionable/results
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import pkg/constantine/math/arithmetic
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import ../../merkletree
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func extractLowBits*[n: static int](elm: BigInt[n], k: int): uint64 =
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doAssert(k > 0 and k <= 64)
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var r = 0'u64
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for i in 0 ..< k:
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let b = bit[n](elm, i)
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let y = uint64(b)
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if (y != 0):
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r = bitor(r, 1'u64 shl i)
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r
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func extractLowBits(fld: Poseidon2Hash, k: int): uint64 =
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let elm: BigInt[254] = fld.toBig()
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return extractLowBits(elm, k)
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func floorLog2*(x: int): int =
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doAssert (x > 0)
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var k = -1
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var y = x
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while (y > 0):
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k += 1
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y = y shr 1
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return k
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func ceilingLog2*(x: int): int =
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doAssert (x > 0)
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return (floorLog2(x - 1) + 1)
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func toBlkInSlot*(cell: Natural, numCells: Natural): Natural =
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let log2 = ceilingLog2(numCells)
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doAssert(1 shl log2 == numCells, "`numCells` is assumed to be a power of two")
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return cell div numCells
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func toCellInBlk*(cell: Natural, numCells: Natural): Natural =
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let log2 = ceilingLog2(numCells)
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doAssert(1 shl log2 == numCells, "`numCells` is assumed to be a power of two")
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return cell mod numCells
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func cellIndex*(
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entropy: Poseidon2Hash, slotRoot: Poseidon2Hash, numCells: Natural, counter: Natural
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): Natural =
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let log2 = ceilingLog2(numCells)
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doAssert(1 shl log2 == numCells, "`numCells` is assumed to be a power of two")
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let hash = Sponge.digest(@[entropy, slotRoot, counter.toF], rate = 2)
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return int(extractLowBits(hash, log2))
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func cellIndices*(
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entropy: Poseidon2Hash,
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slotRoot: Poseidon2Hash,
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numCells: Natural,
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nSamples: Natural,
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): seq[Natural] =
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var indices: seq[Natural]
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for i in 1 .. nSamples:
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indices.add(cellIndex(entropy, slotRoot, numCells, i))
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indices
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