function getCurrentAmountBonusRate(uint256 _weiAmount) private constant returns (uint) {
    uint i;
    for(i=0; i<amountBonus.length; i++) {
      if(_weiAmount.mul(rate) >= amountBonus[i].timeOrAmount) {
        return amountBonus[i].rateMultiplier;
      }
    }
    return 100;
  }