safe-math.sol

pragma solidity ^0.5.0; /** * @dev Wrappers over Solidity's arithmetic operations with added overflow * checks. * * Arithmetic operations in Solidity wrap on overflow. This can easily result * in bugs, because programmers usually assume that an overflow raises an * error, which is the standard behavior in high level programming languages. * `SafeMath` restores this intuition by reverting the transaction when an * operation overflows. * * Using this library instead of the unchecked operations eliminates an entire * class of bugs, so it's recommended to use it always. */ library SafeMath { /** * @dev Returns the addition of two unsigned integers, reverting on * overflow. * * Counterpart to Solidity's `+` operator. * * Requirements: * - Addition cannot overflow. */ function add(uint256 a, uint256 b) internal pure returns (uint256) { uint256 c = a + b; require(c >= a, "SafeMath: addition overflow"); return c; } /** * @dev Returns the subtraction of two unsigned integers, reverting on * overflow (when the result is negative). * * Counterpart to Solidity's `-` operator. * * Requirements: * - Subtraction cannot overflow. */ function sub(uint256 a, uint256 b) internal pure returns (uint256) { return sub(a, b, "SafeMath: subtraction overflow"); } /** * @dev Returns the subtraction of two unsigned integers, reverting with custom message on * overflow (when the result is negative). * * Counterpart to Solidity's `-` operator. * * Requirements: * - Subtraction cannot overflow. * * NOTE: This is a feature of the next version of OpenZeppelin Contracts. * @dev Get it via `npm install @openzeppelin/contracts@next`. */ function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) { require(b <= a, errorMessage); uint256 c = a - b; return c; } /** * @dev Returns the multiplication of two unsigned integers, reverting on * overflow. * * Counterpart to Solidity's `*` operator. * * Requirements: * - Multiplication cannot 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: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522 if (a == 0) { return 0; } uint256 c = a * b; require(c / a == b, "SafeMath: multiplication overflow"); return c; } /** * @dev Returns the integer division of two unsigned integers. Reverts on * division by zero. The result is rounded towards zero. * * Counterpart to Solidity's `/` operator. Note: this function uses a * `revert` opcode (which leaves remaining gas untouched) while Solidity * uses an invalid opcode to revert (consuming all remaining gas). * * Requirements: * - The divisor cannot be zero. */ function div(uint256 a, uint256 b) internal pure returns (uint256) { return div(a, b, "SafeMath: division by zero"); } /** * @dev Returns the integer division of two unsigned integers. Reverts with custom message on * division by zero. The result is rounded towards zero. * * Counterpart to Solidity's `/` operator. Note: this function uses a * `revert` opcode (which leaves remaining gas untouched) while Solidity * uses an invalid opcode to revert (consuming all remaining gas). * * Requirements: * - The divisor cannot be zero. * NOTE: This is a feature of the next version of OpenZeppelin Contracts. * @dev Get it via `npm install @openzeppelin/contracts@next`. */ function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) { // Solidity only automatically asserts when dividing by 0 require(b > 0, errorMessage); uint256 c = a / b; // assert(a == b * c + a % b); // There is no case in which this doesn't hold return c; } /** * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo), * Reverts when dividing by zero. * * Counterpart to Solidity's `%` operator. This function uses a `revert` * opcode (which leaves remaining gas untouched) while Solidity uses an * invalid opcode to revert (consuming all remaining gas). * * Requirements: * - The divisor cannot be zero. */ function mod(uint256 a, uint256 b) internal pure returns (uint256) { return mod(a, b, "SafeMath: modulo by zero"); } /** * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo), * Reverts with custom message when dividing by zero. * * Counterpart to Solidity's `%` operator. This function uses a `revert` * opcode (which leaves remaining gas untouched) while Solidity uses an * invalid opcode to revert (consuming all remaining gas). * * Requirements: * - The divisor cannot be zero. * * NOTE: This is a feature of the next version of OpenZeppelin Contracts. * @dev Get it via `npm install @openzeppelin/contracts@next`. */ function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) { require(b != 0, errorMessage); return a % b; } }