openzeppelin-solidity

[Grapheneum]

pragma solidity ^0.4.24;

/**

• @title SafeMath
• @dev Math operations with safety checks that revert on error
  */
  library SafeMath {

/**

• @dev Multiplies two numbers, reverts on overflow.
  */
  function mul(uint256 _a, uint256 _b) internal pure returns (uint256) {
  // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
  // benefit is lost if 'b' is also tested.
  // See: OpenZeppelin/openzeppelin-contracts#522
  if (_a == 0) {
  return 0;
  }

  uint256 c = _a * _b;
  require(c / _a == _b);

  return c;
  }

/**

• @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
  */
  function div(uint256 _a, uint256 _b) internal pure returns (uint256) {
  require(_b > 0); // Solidity only automatically asserts when dividing by 0
  uint256 c = _a / _b;
  // assert(_a == _b * c + _a % _b); // There is no case in which this doesn't hold

  return c;
  }

/**

• @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
  require(_b <= _a);
  uint256 c = _a - _b;

  return c;
  }

/**

• @dev Adds two numbers, reverts on overflow.
  */
  function add(uint256 _a, uint256 _b) internal pure returns (uint256) {
  uint256 c = _a + _b;
  require(c >= _a);

  return c;
  }

/**

• @dev Divides two numbers and returns the remainder (unsigned integer modulo),
• reverts when dividing by zero.
  */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
  require(b != 0);
  return a % b;
  }
  }

[Tadej Vengust]

Yes this code is copied from open zeppelin which is under MIT license.