message: [fix] fix shift error when fuzzing accumulator schema
  Closes:
diff: @@ -61,10 +61,10 @@ impl Position {
  /// pos count start from 0 on each level
  pub fn from_level_and_pos(level: u32, pos: u64) -> Self {
  - precondition!(level < 63);
  + precondition!(level < 64);
  assume!(1u64 << level > 0); // bitwise and integer operations don't mix.
  let level_one_bits = (1u64 << level) - 1;
  - let shifted_pos = pos << (level + 1);
  + let shifted_pos = if level == 63 { 0 } else { pos << (level + 1) };
  Position(shifted_pos | level_one_bits)
  }
  @@ -78,8 +78,8 @@ impl Position {
  pub fn from_postorder_index(index: u64) -> Result<Self> {
  ensure!(
  - index < (!0u64 >> 2),
  - "node index {} is invalid (greater than 2^63 - 1)",
  + index < !0u64,
  + "node index {} is invalid (equal to 2^64 - 1)",
  index
  );
  Ok(Position(postorder_to_inorder(index)))
  