reveal_bit.zok

import "hashes/sha256/512bit" as sha256
import "utils/casts/u32_to_bits" as u32_to_bits

// Reveal a bit from a 512 bit value, and return it with the corresponding hash

def main(private u32[16] preimage, u32 bitNumber) -> (u32[8], bool):

  // Converting the preimage to bits
  // boolean array 512 boolean values all set to false.

  bool[512] preimageBits = [false; 512]
  for u32 i in 0..16 do
    bool[32] val = u32_to_bits(preimage[i])
    for u32 bit in 0..32 do
      preimageBits[i*32+bit] = val[bit]
    endfor
  endfor
  
  return sha256(preimage[0..8], preimage[8..16]), preimageBits[bitNumber]