Safe casting (#50)

* use safeCast for integer casting

* fix overflow issue

* remove unnecessary using keyword; get contract size under limit

* pr feedback

---------

Co-authored-by: Mike <[email protected]>

Author: MikeHathaway

src/grants/GrantFund.sol

@@ -2,9 +2,10 @@
 
 pragma solidity 0.8.16;
 
-import { Governor }    from "@oz/governance/Governor.sol";
-import { IGovernor }   from "@oz/governance/IGovernor.sol";
-import { IVotes }      from "@oz/governance/utils/IVotes.sol";
+import { Governor }  from "@oz/governance/Governor.sol";
+import { IGovernor } from "@oz/governance/IGovernor.sol";
+import { IVotes }    from "@oz/governance/utils/IVotes.sol";
+import { SafeCast }  from "@oz/utils/math/SafeCast.sol";
 
 import { Maths } from "./libraries/Maths.sol";
 
@@ -124,7 +125,7 @@ contract GrantFund is IGrantFund, ExtraordinaryFunding, StandardFunding {
             // set initial voting power and remaining voting power
             if (voter.votingPower == 0) {
 
-                uint128 newVotingPower = uint128(_getFundingStageVotingPower(msg.sender, screeningStageEndBlock));
+                uint128 newVotingPower = SafeCast.toUint128(_getFundingStageVotingPower(msg.sender, screeningStageEndBlock));
 
                 voter.votingPower          = newVotingPower;
                 voter.remainingVotingPower = newVotingPower;
@@ -239,7 +240,7 @@ contract GrantFund is IGrantFund, ExtraordinaryFunding, StandardFunding {
                 // set initial voting power and remaining voting power
                 if (voter.votingPower == 0) {
 
-                    uint128 newVotingPower = uint128(_getFundingStageVotingPower(msg.sender, screeningStageEndBlock));
+                    uint128 newVotingPower = SafeCast.toUint128(_getFundingStageVotingPower(msg.sender, screeningStageEndBlock));
 
                     voter.votingPower          = newVotingPower;
                     voter.remainingVotingPower = newVotingPower;

src/grants/base/ExtraordinaryFunding.sol

@@ -2,7 +2,8 @@
 
 pragma solidity 0.8.16;
 
-import { IERC20 } from "@oz/token/ERC20/IERC20.sol";
+import { IERC20 }   from "@oz/token/ERC20/IERC20.sol";
+import { SafeCast } from "@oz/utils/math/SafeCast.sol";
 
 import { Funding } from "./Funding.sol";
 
@@ -47,6 +48,7 @@ abstract contract ExtraordinaryFunding is Funding, IExtraordinaryFunding {
 
         ExtraordinaryFundingProposal storage proposal = extraordinaryFundingProposals[proposalId_];
 
+        // since we are casting from uint128 to uint256, we can safely assume that the value will not overflow
         uint256 tokensRequested = uint256(proposal.tokensRequested);
 
         // revert if executed or if the proposal has received more votes than minimumThreshold and tokensRequestedPercentage of all tokens
@@ -95,8 +97,8 @@ abstract contract ExtraordinaryFunding is Funding, IExtraordinaryFunding {
 
         // store newly created proposal
         newProposal.proposalId      = proposalId_;
-        newProposal.startBlock      = uint128(block.number);
-        newProposal.endBlock        = uint128(endBlock_);
+        newProposal.startBlock      = SafeCast.toUint128(block.number);
+        newProposal.endBlock        = SafeCast.toUint128(endBlock_);
         newProposal.tokensRequested = totalTokensRequested;
 
         emit ProposalCreated(
@@ -137,7 +139,7 @@ abstract contract ExtraordinaryFunding is Funding, IExtraordinaryFunding {
 
         // check voting power at snapshot block
         votes_ = _getVotes(account_, block.number, abi.encode(proposalId_));
-        proposal.votesReceived += uint112(votes_);
+        proposal.votesReceived += SafeCast.toUint112(votes_);
 
         // record that voter has voted on this extraorindary funding proposal
         hasVotedExtraordinary[proposalId_][account_] = true;

src/grants/base/Funding.sol

@@ -4,6 +4,7 @@ pragma solidity 0.8.16;
 
 import { Governor }        from "@oz/governance/Governor.sol";
 import { ReentrancyGuard } from "@oz/security/ReentrancyGuard.sol";
+import { SafeCast }        from "@oz/utils/math/SafeCast.sol";
 
 abstract contract Funding is Governor, ReentrancyGuard {
 
@@ -118,7 +119,7 @@ abstract contract Funding is Governor, ReentrancyGuard {
             }
 
             // update tokens requested for additional calldata
-            tokensRequested_ += uint128(tokensRequested);
+            tokensRequested_ += SafeCast.toUint128(tokensRequested);
 
             unchecked { ++i; }
         }

src/grants/base/StandardFunding.sol

@@ -2,8 +2,9 @@
 
 pragma solidity 0.8.16;
 
-import { IERC20 }      from "@oz/token/ERC20/IERC20.sol";
-import { SafeERC20 }   from "@oz/token/ERC20/utils/SafeERC20.sol";
+import { IERC20 }    from "@oz/token/ERC20/IERC20.sol";
+import { SafeCast }  from "@oz/utils/math/SafeCast.sol";
+import { SafeERC20 } from "@oz/token/ERC20/utils/SafeERC20.sol";
 
 import { Funding } from "./Funding.sol";
 
@@ -128,7 +129,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
         }
 
         // set the distribution period to start at the current block
-        uint48 startBlock = uint48(block.number);
+        uint48 startBlock = SafeCast.toUint48(block.number);
         uint48 endBlock = startBlock + DISTRIBUTION_PERIOD_LENGTH;
 
         // set new value for currentDistributionId
@@ -140,7 +141,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
         newDistributionPeriod.startBlock      = startBlock;
         newDistributionPeriod.endBlock        = endBlock;
         uint256 gbc                           = Maths.wmul(treasury, GLOBAL_BUDGET_CONSTRAINT);
-        newDistributionPeriod.fundsAvailable  = uint128(gbc);
+        newDistributionPeriod.fundsAvailable  = SafeCast.toUint128(gbc);
 
         // decrease the treasury by the amount that is held for allocation in the new distribution period
         treasury -= gbc;
@@ -180,6 +181,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
 
     /**
      * @notice Updates Treasury with surplus funds from distribution.
+     * @dev    Counters incremented in an unchecked block due to being bounded by array length of at most 10.
      * @param distributionId_ distribution Id of updating distribution 
      */
     function _updateTreasury(
@@ -319,7 +321,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
             if (proposal.fundingVotesReceived < 0) return false;
 
             // update counters
-            sum += uint128(proposal.fundingVotesReceived);
+            sum += uint128(proposal.fundingVotesReceived); // since we are converting from int128 to uint128, we can safely assume that the value will not overflow
             totalTokensRequested += proposal.tokensRequested;
 
             // check if slate of proposals exceeded budget constraint ( 90% of GBC )
@@ -452,14 +454,15 @@ abstract contract StandardFunding is Funding, IStandardFunding {
     /**
      * @notice Calculates the sum of funding votes allocated to a list of proposals.
      * @dev    Only iterates through a maximum of 10 proposals that made it through the screening round.
-     * @dev    Counters incremented in an unchecked block due to being bounded by array length.
+     * @dev    Counters incremented in an unchecked block due to being bounded by array length of at most 10.
      * @param  proposalIdSubset_ Array of proposal Ids to sum.
      * @return sum_ The sum of the funding votes across the given proposals.
      */
     function _sumProposalFundingVotes(
         uint256[] memory proposalIdSubset_
     ) internal view returns (uint128 sum_) {
         for (uint i = 0; i < proposalIdSubset_.length;) {
+            // since we are converting from int128 to uint128, we can safely assume that the value will not overflow
             sum_ += uint128(standardFundingProposals[proposalIdSubset_[i]].fundingVotesReceived);
 
             unchecked { ++i; }
@@ -505,6 +508,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
 
         // voter had already cast a funding vote on this proposal
         if (voteCastIndex != -1) {
+            // since we are converting from int256 to uint256, we can safely assume that the value will not overflow
             FundingVoteParams storage existingVote = votesCast[uint256(voteCastIndex)];
 
             // can't change the direction of a previous vote
@@ -524,7 +528,10 @@ abstract contract StandardFunding is Funding, IStandardFunding {
         }
 
         // calculate the cumulative cost of all votes made by the voter
-        uint128 cumulativeVotePowerUsed = uint128(_sumSquareOfVotesCast(votesCast));
+        // and check that attempted votes cast doesn't overflow uint128
+        uint256 sumOfTheSquareOfVotesCast = _sumSquareOfVotesCast(votesCast);
+        if (sumOfTheSquareOfVotesCast > type(uint128).max) revert InsufficientVotingPower();
+        uint128 cumulativeVotePowerUsed = SafeCast.toUint128(sumOfTheSquareOfVotesCast);
 
         // check that the voter has enough voting power remaining to cast the vote
         if (cumulativeVotePowerUsed > votingPower) revert InsufficientVotingPower();
@@ -533,17 +540,17 @@ abstract contract StandardFunding is Funding, IStandardFunding {
         voter_.remainingVotingPower = votingPower - cumulativeVotePowerUsed;
 
         // calculate the change in voting power used by the voter in this vote in order to accurately track the total voting power used in the funding stage
+        // since we are moving from uint128 to uint256, we can safely assume that the value will not overflow
         uint256 incrementalVotingPowerUsed = uint256(cumulativeVotePowerUsed - voterPowerUsedPreVote);
 
         // update accumulator for total voting power used in the funding stage in order to calculate delegate rewards
         currentDistribution_.fundingVotePowerCast += incrementalVotingPowerUsed;
 
         // update proposal vote tracking
-        proposal_.fundingVotesReceived += int128(voteParams_.votesUsed);
+        proposal_.fundingVotesReceived += SafeCast.toInt128(voteParams_.votesUsed);
 
-        // the incremental additional votes cast on the proposal
-        // used as a return value and emit value
-        incrementalVotesUsed_ = uint256(Maths.abs(voteParams_.votesUsed));
+        // the incremental additional votes cast on the proposal to be used as a return value and emit value
+        incrementalVotesUsed_ = SafeCast.toUint256(Maths.abs(voteParams_.votesUsed));
 
         // emit VoteCast instead of VoteCastWithParams to maintain compatibility with Tally
         // emits the amount of incremental votes cast for the proposal, not the voting power cost or total votes on a proposal
@@ -576,7 +583,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
         uint256 proposalId = proposal_.proposalId;
 
         // update proposal votes counter
-        proposal_.votesReceived += uint128(votes_);
+        proposal_.votesReceived += SafeCast.toUint128(votes_);
 
         // check if proposal was already screened
         int indexInArray = _findProposalIndex(proposalId, currentTopTenProposals);
@@ -659,6 +666,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
     ) internal pure returns (int256 index_) {
         index_ = -1; // default value indicating proposalId not in the array
 
+        // since we are converting from uint256 to int256, we can safely assume that the value will not overflow
         int256 numVotesCast = int256(voteParams_.length);
         for (int256 i = 0; i < numVotesCast; ) {
             //slither-disable-next-line incorrect-equality
@@ -675,6 +683,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
      * @notice Sort the 10 proposals which will make it through screening and move on to the funding round.
      * @dev    Implements the descending insertion sort algorithm.
      * @dev    Counters incremented in an unchecked block due to being bounded by array length.
+     * @dev    Since we are converting from int256 to uint256, we can safely assume that the values will not overflow.
      * @param arr_ The array of proposals to sort by votes recieved.
      */
     function _insertionSortProposalsByVotes(
@@ -713,7 +722,7 @@ abstract contract StandardFunding is Funding, IStandardFunding {
         uint256 numVotesCast = votesCast_.length;
 
         for (uint256 i = 0; i < numVotesCast; ) {
-            votesCastSumSquared_ += Maths.wpow(uint256(Maths.abs(votesCast_[i].votesUsed)), 2);
+            votesCastSumSquared_ += Maths.wpow(SafeCast.toUint256(Maths.abs(votesCast_[i].votesUsed)), 2);
 
             unchecked { ++i; }
         }