Contract Source Code:
// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;
pragma experimental ABIEncoderV2;
contract Dop {
/// @notice EIP-20 token name for this token
string public constant name = "Drops Ownership Power";
/// @notice EIP-20 token symbol for this token
string public constant symbol = "DOP";
/// @notice EIP-20 token decimals for this token
uint8 public constant decimals = 18;
/// @notice Total number of tokens in circulation
uint256 public constant totalSupply = 15000000e18; // 15m
/// @notice Allowance amounts on behalf of others
mapping(address => mapping(address => uint96)) internal allowances;
/// @notice Official record of token balances for each account
mapping(address => uint96) internal balances;
/// @notice A record of each accounts delegate
mapping(address => address) public delegates;
/// @notice A checkpoint for marking number of votes from a given block
struct Checkpoint {
uint32 fromBlock;
uint96 votes;
}
/// @notice A record of votes checkpoints for each account, by index
mapping(address => mapping(uint32 => Checkpoint)) public checkpoints;
/// @notice The number of checkpoints for each account
mapping(address => uint32) public numCheckpoints;
/// @notice The EIP-712 typehash for the contract's domain
bytes32 public constant DOMAIN_TYPEHASH =
keccak256(
"EIP712Domain(string name,uint256 chainId,address verifyingContract)"
);
/// @notice The EIP-712 typehash for the delegation struct used by the contract
bytes32 public constant DELEGATION_TYPEHASH =
keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");
/// @notice A record of states for signing / validating signatures
mapping(address => uint256) public nonces;
/// @notice An event thats emitted when an account changes its delegate
event DelegateChanged(
address indexed delegator,
address indexed fromDelegate,
address indexed toDelegate
);
/// @notice An event thats emitted when a delegate account's vote balance changes
event DelegateVotesChanged(
address indexed delegate,
uint256 previousBalance,
uint256 newBalance
);
/// @notice The standard EIP-20 transfer event
event Transfer(address indexed from, address indexed to, uint256 amount);
/// @notice The standard EIP-20 approval event
event Approval(
address indexed owner,
address indexed spender,
uint256 amount
);
/**
* @notice Construct a new Comp token
* @param account The initial account to grant all the tokens
*/
constructor(address account) public {
balances[account] = uint96(totalSupply);
emit Transfer(address(0), account, totalSupply);
}
/**
* @notice Get the number of tokens `spender` is approved to spend on behalf of `account`
* @param account The address of the account holding the funds
* @param spender The address of the account spending the funds
* @return The number of tokens approved
*/
function allowance(address account, address spender)
external
view
returns (uint256)
{
return allowances[account][spender];
}
/**
* @notice Approve `spender` to transfer up to `amount` from `src`
* @dev This will overwrite the approval amount for `spender`
* and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
* @param spender The address of the account which may transfer tokens
* @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
* @return Whether or not the approval succeeded
*/
function approve(address spender, uint256 rawAmount)
external
returns (bool)
{
uint96 amount;
if (rawAmount == uint256(-1)) {
amount = uint96(-1);
} else {
amount = safe96(rawAmount, "Comp::approve: amount exceeds 96 bits");
}
allowances[msg.sender][spender] = amount;
emit Approval(msg.sender, spender, amount);
return true;
}
/**
* @notice Get the number of tokens held by the `account`
* @param account The address of the account to get the balance of
* @return The number of tokens held
*/
function balanceOf(address account) external view returns (uint256) {
return balances[account];
}
/**
* @notice Transfer `amount` tokens from `msg.sender` to `dst`
* @param dst The address of the destination account
* @param rawAmount The number of tokens to transfer
* @return Whether or not the transfer succeeded
*/
function transfer(address dst, uint256 rawAmount) external returns (bool) {
uint96 amount =
safe96(rawAmount, "Comp::transfer: amount exceeds 96 bits");
_transferTokens(msg.sender, dst, amount);
return true;
}
/**
* @notice Transfer `amount` tokens from `src` to `dst`
* @param src The address of the source account
* @param dst The address of the destination account
* @param rawAmount The number of tokens to transfer
* @return Whether or not the transfer succeeded
*/
function transferFrom(
address src,
address dst,
uint256 rawAmount
) external returns (bool) {
address spender = msg.sender;
uint96 spenderAllowance = allowances[src][spender];
uint96 amount =
safe96(rawAmount, "Comp::approve: amount exceeds 96 bits");
if (spender != src && spenderAllowance != uint96(-1)) {
uint96 newAllowance =
sub96(
spenderAllowance,
amount,
"Comp::transferFrom: transfer amount exceeds spender allowance"
);
allowances[src][spender] = newAllowance;
emit Approval(src, spender, newAllowance);
}
_transferTokens(src, dst, amount);
return true;
}
/**
* @notice Delegate votes from `msg.sender` to `delegatee`
* @param delegatee The address to delegate votes to
*/
function delegate(address delegatee) public {
return _delegate(msg.sender, delegatee);
}
/**
* @notice Delegates votes from signatory to `delegatee`
* @param delegatee The address to delegate votes to
* @param nonce The contract state required to match the signature
* @param expiry The time at which to expire the signature
* @param v The recovery byte of the signature
* @param r Half of the ECDSA signature pair
* @param s Half of the ECDSA signature pair
*/
function delegateBySig(
address delegatee,
uint256 nonce,
uint256 expiry,
uint8 v,
bytes32 r,
bytes32 s
) public {
bytes32 domainSeparator =
keccak256(
abi.encode(
DOMAIN_TYPEHASH,
keccak256(bytes(name)),
getChainId(),
address(this)
)
);
bytes32 structHash =
keccak256(
abi.encode(DELEGATION_TYPEHASH, delegatee, nonce, expiry)
);
bytes32 digest =
keccak256(
abi.encodePacked("\x19\x01", domainSeparator, structHash)
);
address signatory = ecrecover(digest, v, r, s);
require(
signatory != address(0),
"Comp::delegateBySig: invalid signature"
);
require(
nonce == nonces[signatory]++,
"Comp::delegateBySig: invalid nonce"
);
require(now <= expiry, "Comp::delegateBySig: signature expired");
return _delegate(signatory, delegatee);
}
/**
* @notice Gets the current votes balance for `account`
* @param account The address to get votes balance
* @return The number of current votes for `account`
*/
function getCurrentVotes(address account) external view returns (uint96) {
uint32 nCheckpoints = numCheckpoints[account];
return
nCheckpoints > 0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
}
/**
* @notice Determine the prior number of votes for an account as of a block number
* @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
* @param account The address of the account to check
* @param blockNumber The block number to get the vote balance at
* @return The number of votes the account had as of the given block
*/
function getPriorVotes(address account, uint256 blockNumber)
public
view
returns (uint96)
{
require(
blockNumber < block.number,
"Comp::getPriorVotes: not yet determined"
);
uint32 nCheckpoints = numCheckpoints[account];
if (nCheckpoints == 0) {
return 0;
}
// First check most recent balance
if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
return checkpoints[account][nCheckpoints - 1].votes;
}
// Next check implicit zero balance
if (checkpoints[account][0].fromBlock > blockNumber) {
return 0;
}
uint32 lower = 0;
uint32 upper = nCheckpoints - 1;
while (upper > lower) {
uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
Checkpoint memory cp = checkpoints[account][center];
if (cp.fromBlock == blockNumber) {
return cp.votes;
} else if (cp.fromBlock < blockNumber) {
lower = center;
} else {
upper = center - 1;
}
}
return checkpoints[account][lower].votes;
}
function _delegate(address delegator, address delegatee) internal {
address currentDelegate = delegates[delegator];
uint96 delegatorBalance = balances[delegator];
delegates[delegator] = delegatee;
emit DelegateChanged(delegator, currentDelegate, delegatee);
_moveDelegates(currentDelegate, delegatee, delegatorBalance);
}
function _transferTokens(
address src,
address dst,
uint96 amount
) internal {
require(
src != address(0),
"Comp::_transferTokens: cannot transfer from the zero address"
);
require(
dst != address(0),
"Comp::_transferTokens: cannot transfer to the zero address"
);
balances[src] = sub96(
balances[src],
amount,
"Comp::_transferTokens: transfer amount exceeds balance"
);
balances[dst] = add96(
balances[dst],
amount,
"Comp::_transferTokens: transfer amount overflows"
);
emit Transfer(src, dst, amount);
_moveDelegates(delegates[src], delegates[dst], amount);
}
function _moveDelegates(
address srcRep,
address dstRep,
uint96 amount
) internal {
if (srcRep != dstRep && amount > 0) {
if (srcRep != address(0)) {
uint32 srcRepNum = numCheckpoints[srcRep];
uint96 srcRepOld =
srcRepNum > 0
? checkpoints[srcRep][srcRepNum - 1].votes
: 0;
uint96 srcRepNew =
sub96(
srcRepOld,
amount,
"Comp::_moveVotes: vote amount underflows"
);
_writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
}
if (dstRep != address(0)) {
uint32 dstRepNum = numCheckpoints[dstRep];
uint96 dstRepOld =
dstRepNum > 0
? checkpoints[dstRep][dstRepNum - 1].votes
: 0;
uint96 dstRepNew =
add96(
dstRepOld,
amount,
"Comp::_moveVotes: vote amount overflows"
);
_writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
}
}
}
function _writeCheckpoint(
address delegatee,
uint32 nCheckpoints,
uint96 oldVotes,
uint96 newVotes
) internal {
uint32 blockNumber =
safe32(
block.number,
"Comp::_writeCheckpoint: block number exceeds 32 bits"
);
if (
nCheckpoints > 0 &&
checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber
) {
checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
} else {
checkpoints[delegatee][nCheckpoints] = Checkpoint(
blockNumber,
newVotes
);
numCheckpoints[delegatee] = nCheckpoints + 1;
}
emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
}
function safe32(uint256 n, string memory errorMessage)
internal
pure
returns (uint32)
{
require(n < 2**32, errorMessage);
return uint32(n);
}
function safe96(uint256 n, string memory errorMessage)
internal
pure
returns (uint96)
{
require(n < 2**96, errorMessage);
return uint96(n);
}
function add96(
uint96 a,
uint96 b,
string memory errorMessage
) internal pure returns (uint96) {
uint96 c = a + b;
require(c >= a, errorMessage);
return c;
}
function sub96(
uint96 a,
uint96 b,
string memory errorMessage
) internal pure returns (uint96) {
require(b <= a, errorMessage);
return a - b;
}
function getChainId() internal pure returns (uint256) {
uint256 chainId;
assembly {
chainId := chainid()
}
return chainId;
}
}