// SPDX-License-Identifier: MIT
pragma solidity ^0.6.12;

/**
 * @title Safe math library
 *
 * @dev Based on https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v3.3.0/contracts/math/SafeMath.sol
 */
library SafeMathLib {
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;

    require(c >= a, "SafeMathLib: addition overflow");

    return c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    return sub(a, b, "SafeMathLib: subtraction overflow");
  }

  function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b <= a, errorMessage);

    return a - b;
  }

  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;

    require(c / a == b, "SafeMathLib: multiplication overflow");

    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return div(a, b, "SafeMathLib: division by zero");
  }

  function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b > 0, errorMessage);

    return a / b;
  }

  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    return mod(a, b, "SafeMathLib: modulo by zero");
  }

  function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b != 0, errorMessage);

    return a % b;
  }
}