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https://github.com/logos-storage/logos-storage-nim.git
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64 lines
1.7 KiB
Nim
64 lines
1.7 KiB
Nim
import ../contracts/requests
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import std/bitops
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import std/sugar
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import pkg/constantine/math/arithmetic
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import pkg/poseidon2/types
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import pkg/poseidon2
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import misc
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type
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DSFieldElement* = F
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DSCellIndex* = uint64
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const
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# Size of a cell.
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# A cell is a sample of storage-data selected for proving.
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CellSize* = u256(2048)
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func extractLowBits*[n: static int](A: BigInt[n], k: int): uint64 =
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assert(k > 0 and k <= 64)
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var r: uint64 = 0
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for i in 0..<k:
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# A is big-endian. Run index backwards: n-1-i
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#let b = bit[n](A, n-1-i)
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let b = bit[n](A, 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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return r
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proc getCellIndex(fe: DSFieldElement, numberOfCells: int): uint64 =
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let log2 = ceilingLog2(numberOfCells)
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assert((1 shl log2) == numberOfCells , "expected `numberOfCells` to be a power of two.")
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return extractLowBits(fe.toBig(), log2)
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proc getNumberOfCellsInSlot*(slot: Slot): int =
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(slot.request.ask.slotSize div CellSize).truncate(int)
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proc findCellIndex*(
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slotRootHash: DSFieldElement,
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challenge: DSFieldElement,
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counter: DSFieldElement,
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numberOfCells: int): DSCellIndex =
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# Computes the cell index for a single sample.
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let
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input = @[slotRootHash, challenge, counter]
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hash = Sponge.digest(input, rate = 2)
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index = getCellIndex(hash, numberOfCells)
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return index
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func findCellIndices*(
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slot: Slot,
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slotRootHash: DSFieldElement,
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challenge: DSFieldElement,
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nSamples: int): seq[DSCellIndex] =
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# Computes nSamples cell indices.
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let numberOfCells = getNumberOfCellsInSlot(slot)
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return collect(newSeq, (for i in 1..nSamples: findCellIndex(slotRootHash, challenge, toF(i), numberOfCells)))
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