fn update_global_index(state: &mut State, reward_balance: Uint128) -> StdResult<()> {
    // Zero staking balance check
    if state.total_balance.is_zero() {
        // nothing balance, skip update
        return Ok(());
    }

    // No change check
    if state.prev_reward_balance == reward_balance {
        // balance didnt change, skip update
        return Ok(());
    }

    // claimed_rewards = current_balance - prev_balance;
    let claimed_rewards = reward_balance.checked_sub(state.prev_reward_balance)?;

    // update state
    state.prev_reward_balance = reward_balance;
    // global_index += claimed_rewards / total_balance;
    state.global_index = decimal_summation_in_256(
        state.global_index,
        Decimal::from_ratio(claimed_rewards, state.total_balance),
    );

    Ok(())
}
