nim-poseidon2/poseidon2.nim

import constantine/math/arithmetic

import poseidon2/types
import poseidon2/permutation
import poseidon2/io
import poseidon2/sponge

export sponge
export toBytes


#-------------------------------------------------------------------------------

# 2-to-1 compression
func compress*(a, b : F) : F =
  var x = a
  var y = b
  var z : F ; setZero(z)
  permInplace(x, y, z)
  return x

func merkleRoot*(xs: openArray[F]) : F =
  let a = low(xs)
  let b = high(xs)
  let m = b-a+1

  if m==1:
    return xs[a]

  else:
    let halfn  : int  = m div 2
    let n      : int  = 2*halfn
    let isOdd : bool = (n != m)

    var ys : seq[F]
    if not isOdd:
      ys = newSeq[F](halfn)
    else:
      ys = newSeq[F](halfn+1)

    for i in 0..<halfn:
      ys[i] = compress( xs[a+2*i], xs[a+2*i+1] )
    if isOdd:
      ys[halfn] = compress( xs[n], zero )

    return merkleRoot(ys)

func merkleRoot*(bytes: openArray[byte]): F =
  merkleRoot(seq[F].fromBytes(bytes))

#-------------------------------------------------------------------------------