contract ERC20 is IERC20 { using SafeMath for uint256; mapping (address => uint256) private _balances; mapping (address => mapping (address => uint256)) private _allowances; uint256 private _totalSupply; /** * @dev Total number of tokens in existence. */ function totalSupply() public view returns (uint256) { return _totalSupply; } /** * @dev Gets the balance of the specified address. * @param owner The address to query the balance of. * @return A uint256 representing the amount owned by the passed address. */ function balanceOf(address owner) public view returns (uint256) { return _balances[owner]; } /** * @dev Function to check the amount of tokens that an owner allowed to a spender. * @param owner address The address which owns the funds. * @param spender address The address which will spend the funds. * @return A uint256 specifying the amount of tokens still available for the spender. */ function allowance(address owner, address spender) public view returns (uint256) { return _allowances[owner][spender]; } /** * @dev Transfer token to a specified address. * @param to The address to transfer to. * @param value The amount to be transferred. */ function transfer(address to, uint256 value) public returns (bool) { _transfer(msg.sender, to, value); return true; } /** * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender. * Beware that changing an allowance with this method brings the risk that someone may use both the old * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards: * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 * @param spender The address which will spend the funds. * @param value The amount of tokens to be spent. */ function approve(address spender, uint256 value) public returns (bool) { _approve(msg.sender, spender, value); return true; } /** * @dev Transfer tokens from one address to another. * Note that while this function emits an Approval event, this is not required as per the specification, * and other compliant implementations may not emit the event. * @param from address The address which you want to send tokens from * @param to address The address which you want to transfer to * @param value uint256 the amount of tokens to be transferred */ function transferFrom(address from, address to, uint256 value) public returns (bool) { _transfer(from, to, value); _approve(from, msg.sender, _allowances[from][msg.sender].sub(value)); return true; } /** * @dev Increase the amount of tokens that an owner allowed to a spender. * approve should be called when _allowances[msg.sender][spender] == 0. To increment * allowed value is better to use this function to avoid 2 calls (and wait until * the first transaction is mined) * From MonolithDAO Token.sol * Emits an Approval event. * @param spender The address which will spend the funds. * @param addedValue The amount of tokens to increase the allowance by. */ function increaseAllowance(address spender, uint256 addedValue) public returns (bool) { _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue)); return true; } /** * @dev Decrease the amount of tokens that an owner allowed to a spender. * approve should be called when _allowances[msg.sender][spender] == 0. To decrement * allowed value is better to use this function to avoid 2 calls (and wait until * the first transaction is mined) * From MonolithDAO Token.sol * Emits an Approval event. * @param spender The address which will spend the funds. * @param subtractedValue The amount of tokens to decrease the allowance by. */ function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) { _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue)); return true; } /** * @dev Transfer token for a specified addresses. * @param from The address to transfer from. * @param to The address to transfer to. * @param value The amount to be transferred. */ function _transfer(address from, address to, uint256 value) internal { require(to != address(0), "ERC20: transfer to the zero address"); _balances[from] = _balances[from].sub(value); _balances[to] = _balances[to].add(value); emit Transfer(from, to, value); } /** * @dev Internal function that mints an amount of the token and assigns it to * an account. This encapsulates the modification of balances such that the * proper events are emitted. * @param account The account that will receive the created tokens. * @param value The amount that will be created. */ function _mint(address account, uint256 value) internal { require(account != address(0), "ERC20: mint to the zero address"); _totalSupply = _totalSupply.add(value); _balances[account] = _balances[account].add(value); emit Transfer(address(0), account, value); } /** * @dev Internal function that burns an amount of the token of a given * account. * @param account The account whose tokens will be burnt. * @param value The amount that will be burnt. */ function _burn(address account, uint256 value) internal { require(account != address(0), "ERC20: burn from the zero address"); _totalSupply = _totalSupply.sub(value); _balances[account] = _balances[account].sub(value); emit Transfer(account, address(0), value); } /** * @dev Approve an address to spend another addresses' tokens. * @param owner The address that owns the tokens. * @param spender The address that will spend the tokens. * @param value The number of tokens that can be spent. */ function _approve(address owner, address spender, uint256 value) internal { require(owner != address(0), "ERC20: approve from the zero address"); require(spender != address(0), "ERC20: approve to the zero address"); _allowances[owner][spender] = value; emit Approval(owner, spender, value); } /** * @dev Internal function that burns an amount of the token of a given * account, deducting from the sender's allowance for said account. Uses the * internal burn function. * Emits an Approval event (reflecting the reduced allowance). * @param account The account whose tokens will be burnt. * @param value The amount that will be burnt. */ function _burnFrom(address account, uint256 value) internal { _burn(account, value); _approve(account, msg.sender, _allowances[account][msg.sender].sub(value)); } }
/** * @title Standard ERC20 token * * @dev Implementation of the basic standard token. * https://eips.ethereum.org/EIPS/eip-20 * Originally based on code by FirstBlood: * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol * * This implementation emits additional Approval events, allowing applications to reconstruct the allowance status for * all accounts just by listening to said events. Note that this isn't required by the specification, and other * compliant implementations may not do it. */
function totalSupply() public view returns (uint256) { return _totalSupply; } /** * @dev Gets the balance of the specified address. * @param owner The address to query the balance of. * @return A uint256 representing the amount owned by the passed address. */ function balanceOf(address owner) public view returns (uint256) { return _balances[owner]; } /** * @dev Function to check the amount of tokens that an owner allowed to a spender. * @param owner address The address which owns the funds. * @param spender address The address which will spend the funds. * @return A uint256 specifying the amount of tokens still available for the spender. */ function allowance(address owner, address spender) public view returns (uint256) { return _allowances[owner][spender]; } /** * @dev Transfer token to a specified address. * @param to The address to transfer to. * @param value The amount to be transferred. */ function transfer(address to, uint256 value) public returns (bool) { _transfer(msg.sender, to, value); return true; } /** * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender. * Beware that changing an allowance with this method brings the risk that someone may use both the old * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards: * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 * @param spender The address which will spend the funds. * @param value The amount of tokens to be spent. */ function approve(address spender, uint256 value) public returns (bool) { _approve(msg.sender, spender, value); return true; } /** * @dev Transfer tokens from one address to another. * Note that while this function emits an Approval event, this is not required as per the specification, * and other compliant implementations may not emit the event. * @param from address The address which you want to send tokens from * @param to address The address which you want to transfer to * @param value uint256 the amount of tokens to be transferred */ function transferFrom(address from, address to, uint256 value) public returns (bool) { _transfer(from, to, value); _approve(from, msg.sender, _allowances[from][msg.sender].sub(value)); return true; } /** * @dev Increase the amount of tokens that an owner allowed to a spender. * approve should be called when _allowances[msg.sender][spender] == 0. To increment * allowed value is better to use this function to avoid 2 calls (and wait until * the first transaction is mined) * From MonolithDAO Token.sol * Emits an Approval event. * @param spender The address which will spend the funds. * @param addedValue The amount of tokens to increase the allowance by. */ function increaseAllowance(address spender, uint256 addedValue) public returns (bool) { _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue)); return true; } /** * @dev Decrease the amount of tokens that an owner allowed to a spender. * approve should be called when _allowances[msg.sender][spender] == 0. To decrement * allowed value is better to use this function to avoid 2 calls (and wait until * the first transaction is mined) * From MonolithDAO Token.sol * Emits an Approval event. * @param spender The address which will spend the funds. * @param subtractedValue The amount of tokens to decrease the allowance by. */ function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) { _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue)); return true; } /** * @dev Transfer token for a specified addresses. * @param from The address to transfer from. * @param to The address to transfer to. * @param value The amount to be transferred. */ function _transfer(address from, address to, uint256 value) internal { require(to != address(0), "ERC20: transfer to the zero address"); _balances[from] = _balances[from].sub(value); _balances[to] = _balances[to].add(value); emit Transfer(from, to, value); } /** * @dev Internal function that mints an amount of the token and assigns it to * an account. This encapsulates the modification of balances such that the * proper events are emitted. * @param account The account that will receive the created tokens. * @param value The amount that will be created. */ function _mint(address account, uint256 value) internal { require(account != address(0), "ERC20: mint to the zero address"); _totalSupply = _totalSupply.add(value); _balances[account] = _balances[account].add(value); emit Transfer(address(0), account, value); } /** * @dev Internal function that burns an amount of the token of a given * account. * @param account The account whose tokens will be burnt. * @param value The amount that will be burnt. */ function _burn(address account, uint256 value) internal { require(account != address(0), "ERC20: burn from the zero address"); _totalSupply = _totalSupply.sub(value); _balances[account] = _balances[account].sub(value); emit Transfer(account, address(0), value); } /** * @dev Approve an address to spend another addresses' tokens. * @param owner The address that owns the tokens. * @param spender The address that will spend the tokens. * @param value The number of tokens that can be spent. */ function _approve(address owner, address spender, uint256 value) internal { require(owner != address(0), "ERC20: approve from the zero address"); require(spender != address(0), "ERC20: approve to the zero address"); _allowances[owner][spender] = value; emit Approval(owner, spender, value); } /** * @dev Internal function that burns an amount of the token of a given * account, deducting from the sender's allowance for said account. Uses the * internal burn function. * Emits an Approval event (reflecting the reduced allowance). * @param account The account whose tokens will be burnt. * @param value The amount that will be burnt. */ function _burnFrom(address account, uint256 value) internal { _burn(account, value); _approve(account, msg.sender, _allowances[account][msg.sender].sub(value)); } }
/** * @dev Internal function that mints an amount of the token and assigns it to * an account. This encapsulates the modification of balances such that the * proper events are emitted. * @param account The account that will receive the created tokens. * @param value The amount that will be created. */