SafeMath.sol

pragma solidity 0.4.18;


contract SafeMath {

  function safeMul(uint a, uint b) internal pure returns (uint) {
    uint c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }
  function safeSub(uint a, uint b) internal pure returns (uint) {
    assert(b <= a);
    return a - b;
  }
  function safeAdd(uint a, uint b) internal pure returns (uint) {
    uint c = a + b;
    assert(c>=a && c>=b);
    return c;
  }

  modifier onlyPayloadSize(uint numWords) {
     assert(msg.data.length >= numWords * 32 + 4);
     _;
  }

}