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TRUST M-8: Reward distribution in RewardableERC20 #994

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merged 8 commits into from
Nov 1, 2023
Merged

TRUST M-8: Reward distribution in RewardableERC20 #994

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ca53604
add buffer for decimals in shares calculations
julianmrodri Oct 26, 2023
0ee0edd
rename var
julianmrodri Oct 26, 2023
aa2fe8a
fix unit tracking in comments
tbrent Oct 31, 2023
4862cef
adjust units and tests
julianmrodri Nov 1, 2023
1495c12
Merge branch 'fix-sharesdecimals' of github.com:reserve-protocol/prot…
julianmrodri Nov 1, 2023
90f4dad
fix lint
julianmrodri Nov 1, 2023
bd8dfd2
fix comments
julianmrodri Nov 1, 2023
620cc5b
fix lint
julianmrodri Nov 1, 2023
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26 changes: 16 additions & 10 deletions contracts/plugins/assets/erc20/RewardableERC20.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,8 @@ import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "../../../interfaces/IRewardable.sol";

uint256 constant SHARE_DECIMAL_OFFSET = 9; // to prevent reward rounding issues

/**
* @title RewardableERC20
* @notice An abstract class that can be extended to create rewardable wrapper.
Expand All @@ -19,11 +21,11 @@ import "../../../interfaces/IRewardable.sol";
abstract contract RewardableERC20 is IRewardable, ERC20, ReentrancyGuard {
using SafeERC20 for IERC20;

uint256 public immutable one; // {qShare/share}
uint256 public immutable one; // 1e9 * {qShare/share}
IERC20 public immutable rewardToken;

uint256 public rewardsPerShare; // {qRewards/share}
mapping(address => uint256) public lastRewardsPerShare; // {qRewards/share}
uint256 public rewardsPerShare; // 1e9 * {qRewards/share}
mapping(address => uint256) public lastRewardsPerShare; // 1e9 * {qRewards/share}
mapping(address => uint256) public accumulatedRewards; // {qRewards}
mapping(address => uint256) public claimedRewards; // {qRewards}

Expand All @@ -35,7 +37,8 @@ abstract contract RewardableERC20 is IRewardable, ERC20, ReentrancyGuard {
/// @dev Extending class must ensure ERC20 constructor is called
constructor(IERC20 _rewardToken, uint8 _decimals) {
rewardToken = _rewardToken;
one = 10**_decimals; // set via pass-in to prevent inheritance issues
// set via pass-in to prevent inheritance issues
one = 10**(_decimals + SHARE_DECIMAL_OFFSET);
}

function claimRewards() external nonReentrant {
Expand All @@ -47,7 +50,7 @@ abstract contract RewardableERC20 is IRewardable, ERC20, ReentrancyGuard {
function _syncAccount(address account) internal {
if (account == address(0)) return;

// {qRewards/share}
// 1e9 * {qRewards/share}
uint256 accountRewardsPerShare = lastRewardsPerShare[account];

// {qShare}
Expand All @@ -56,13 +59,13 @@ abstract contract RewardableERC20 is IRewardable, ERC20, ReentrancyGuard {
// {qRewards}
uint256 _accumulatedRewards = accumulatedRewards[account];

// {qRewards/share}
// 1e9 * {qRewards/share}
uint256 _rewardsPerShare = rewardsPerShare;
if (accountRewardsPerShare < _rewardsPerShare) {
// {qRewards/share}
// 1e9 * {qRewards/share}
uint256 delta = _rewardsPerShare - accountRewardsPerShare;

// {qRewards} = {qRewards/share} * {qShare}
// {qRewards} = (1e9 * {qRewards/share}) * {qShare} / (1e9 * {qShare/share})
_accumulatedRewards += (delta * shares) / one;
}
lastRewardsPerShare[account] = _rewardsPerShare;
Expand All @@ -81,12 +84,15 @@ abstract contract RewardableERC20 is IRewardable, ERC20, ReentrancyGuard {
uint256 _previousBalance = lastRewardBalance;

if (balanceAfterClaimingRewards > _previousBalance) {
uint256 delta = balanceAfterClaimingRewards - _previousBalance;
uint256 delta = balanceAfterClaimingRewards - _previousBalance; // {qRewards}

// 1e9 * {qRewards/share} = {qRewards} * (1e9 * {qShare/share}) / {qShare}
uint256 deltaPerShare = (delta * one) / _totalSupply;

// {qRewards} = {qRewards} + (1e9*(qRewards/share)) * {qShare} / (1e9*{qShare/share})
balanceAfterClaimingRewards = _previousBalance + (deltaPerShare * _totalSupply) / one;

// {qRewards/share} += {qRewards} * {qShare/share} / {qShare}
// 1e9 * {qRewards/share} += {qRewards} * (1e9*{qShare/share}) / {qShare}
_rewardsPerShare += deltaPerShare;
}

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