84 lines
2.1 KiB
Nim
84 lines
2.1 KiB
Nim
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## 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/sugar
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import std/bitops
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import pkg/poseidon2
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import pkg/poseidon2/io
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import pkg/constantine/math/arithmetic
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import pkg/constantine/math/io/io_fields
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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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assert( 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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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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if (x == 0):
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return -1
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else:
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return (floorLog2(x-1) + 1)
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func toBlockIdx*(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 toBlockCellIdx*(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,
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slotRoot: Poseidon2Hash,
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numCells: Natural, counter: 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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let hash = Sponge.digest( @[ slotRoot, entropy, 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, nSamples: Natural): seq[Natural] =
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var indices: seq[Natural]
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while (indices.len < nSamples):
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let idx = cellIndex(entropy, slotRoot, numCells, indices.len + 1)
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indices.add(idx.Natural)
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indices
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