Use checks

contracts/TimeswapPair.sol

@@ -9,7 +9,6 @@ import {BurnMath} from './libraries/BurnMath.sol';
 import {LendMath} from './libraries/LendMath.sol';
 import {WithdrawMath} from './libraries/WithdrawMath.sol';
 import {BorrowMath} from './libraries/BorrowMath.sol';
-import {PayMath} from './libraries/PayMath.sol';
 import {SafeTransfer} from './libraries/SafeTransfer.sol';
 import {Array} from './libraries/Array.sol';
 import {Callback} from './libraries/Callback.sol';
@@ -147,10 +146,10 @@ contract TimeswapPair is IPair {
         )
     {
         require(block.timestamp < maturity, 'E202');
-        require(maturity - block.timestamp < 0x100000000, 'E208');
+        unchecked { require(maturity - block.timestamp < 0x100000000, 'E208'); }
         require(liquidityTo != address(0) && dueTo != address(0), 'E201');
         require(liquidityTo != address(this) && dueTo != address(this), 'E204');
-        require(xIncrease > 0 && yIncrease > 0 && zIncrease > 0, 'E205');
+        require(xIncrease != 0 && yIncrease != 0 && zIncrease != 0, 'E205');
 
         Pool storage pool = pools[maturity];
 
@@ -167,7 +166,7 @@ contract TimeswapPair is IPair {
             pool.state.totalLiquidity += liquidityTotal;
             pool.liquidities[factory.owner()] += liquidityTotal - liquidityOut;
         }
-        require(liquidityOut > 0, 'E212');
+        require(liquidityOut != 0, 'E212');
         pool.liquidities[liquidityTo] += liquidityOut;
 
         dueOut.debt = MintMath.getDebt(maturity, xIncrease, yIncrease);
@@ -200,7 +199,7 @@ contract TimeswapPair is IPair {
         require(block.timestamp >= maturity, 'E203');
         require(assetTo != address(0) && collateralTo != address(0), 'E201');
         require(assetTo != address(this) && collateralTo != address(this), 'E204');
-        require(liquidityIn > 0, 'E205');
+        require(liquidityIn != 0, 'E205');
 
         Pool storage pool = pools[maturity];
 
@@ -211,11 +210,14 @@ contract TimeswapPair is IPair {
 
         pool.liquidities[msg.sender] -= liquidityIn;
 
-        pool.state.reserves.asset -= tokensOut.asset;
-        pool.state.reserves.collateral -= tokensOut.collateral;
-
-        if (tokensOut.asset > 0) asset.safeTransfer(assetTo, tokensOut.asset);
-        if (tokensOut.collateral > 0) collateral.safeTransfer(collateralTo, tokensOut.collateral);
+        if (tokensOut.asset != 0) {
+            pool.state.reserves.asset -= tokensOut.asset;
+            asset.safeTransfer(assetTo, tokensOut.asset);
+        }
+        if (tokensOut.collateral != 0) {
+            pool.state.reserves.collateral -= tokensOut.collateral;
+            collateral.safeTransfer(collateralTo, tokensOut.collateral);
+        }
 
         emit Burn(maturity, msg.sender, assetTo, collateralTo, liquidityIn, tokensOut);
     }
@@ -233,10 +235,10 @@ contract TimeswapPair is IPair {
         require(block.timestamp < maturity, 'E202');
         require(bondTo != address(0) && insuranceTo != address(0), 'E201');
         require(bondTo != address(this) && insuranceTo != address(this), 'E204');
-        require(xIncrease > 0, 'E205');
+        require(xIncrease != 0, 'E205');
 
         Pool storage pool = pools[maturity];
-        require(pool.state.totalLiquidity > 0, 'E206');
+        require(pool.state.totalLiquidity != 0, 'E206');
 
         LendMath.check(pool.state, xIncrease, yDecrease, zDecrease, fee);
 
@@ -271,7 +273,7 @@ contract TimeswapPair is IPair {
         require(block.timestamp >= maturity, 'E203');
         require(assetTo != address(0) && collateralTo != address(0), 'E201');
         require(assetTo != address(this) && collateralTo != address(this), 'E204');
-        require(claimsIn.bond > 0 || claimsIn.insurance > 0, 'E205');
+        require(claimsIn.bond != 0 || claimsIn.insurance != 0, 'E205');
 
         Pool storage pool = pools[maturity];
 
@@ -289,8 +291,8 @@ contract TimeswapPair is IPair {
         pool.state.reserves.asset -= tokensOut.asset;
         pool.state.reserves.collateral -= tokensOut.collateral;
 
-        if (tokensOut.asset > 0) asset.safeTransfer(assetTo, tokensOut.asset);
-        if (tokensOut.collateral > 0) collateral.safeTransfer(collateralTo, tokensOut.collateral);
+        if (tokensOut.asset != 0) asset.safeTransfer(assetTo, tokensOut.asset);
+        if (tokensOut.collateral != 0) collateral.safeTransfer(collateralTo, tokensOut.collateral);
 
         emit Withdraw(maturity, msg.sender, assetTo, collateralTo, claimsIn, tokensOut);
     }
@@ -308,10 +310,10 @@ contract TimeswapPair is IPair {
         require(block.timestamp < maturity, 'E202');
         require(assetTo != address(0) && dueTo != address(0), 'E201');
         require(assetTo != address(this) && dueTo != address(this), 'E204');
-        require(xDecrease > 0, 'E205');
+        require(xDecrease != 0, 'E205');
 
         Pool storage pool = pools[maturity];
-        require(pool.state.totalLiquidity > 0, 'E206');
+        require(pool.state.totalLiquidity != 0, 'E206');
 
         BorrowMath.check(pool.state, xDecrease, yIncrease, zIncrease, fee);
 
@@ -360,18 +362,18 @@ contract TimeswapPair is IPair {
             Due storage due = dues[ids[i]];
             require(due.startBlock != BlockNumber.get(), 'E207');
             if (owner != msg.sender) require(collateralsOut[i] == 0, 'E213');
-            PayMath.checkProportional(assetsIn[i], collateralsOut[i], due);
+            require(uint256(assetIn) * due.collateral >= uint256(collateralOut) * due.debt, 'E303');
             due.debt -= assetsIn[i];
             due.collateral -= collateralsOut[i];
             assetIn += assetsIn[i];
             collateralOut += collateralsOut[i];
         }
-        if (assetIn > 0) Callback.pay(asset, assetIn, data);
+        if (assetIn != 0) Callback.pay(asset, assetIn, data);
 
         pool.state.reserves.asset += assetIn;
         pool.state.reserves.collateral -= collateralOut;
 
-        if (collateralOut > 0) collateral.safeTransfer(to, collateralOut);
+        if (collateralOut != 0) collateral.safeTransfer(to, collateralOut);
 
         emit Pay(maturity, msg.sender, to, owner, ids, assetsIn, collateralsOut, assetIn, collateralOut);
     }

contracts/libraries/FullMath.sol

@@ -31,7 +31,7 @@ library FullMath {
 
             // Handle non-overflow cases, 256 by 256 division
             if (prod1 == 0) {
-                require(denominator > 0);
+                require(denominator != 0);
                 assembly {
                     result := div(prod0, denominator)
                 }
@@ -121,6 +121,6 @@ library FullMath {
         uint256 denominator
     ) internal pure returns (uint256 result) {
         result = mulDiv(a, b, denominator);
-        if (mulmod(a, b, denominator) > 0) result++;
+        if (mulmod(a, b, denominator) != 0) result++;
     }
 }

contracts/libraries/Math.sol

@@ -4,7 +4,7 @@ pragma solidity =0.8.4;
 library Math {
     function divUp(uint256 x, uint256 y) internal pure returns (uint256 z) {
         z = x / y;
-        if (x % y > 0) z++;
+        if (x % y != 0) z++;
     }
 
     function shiftRightUp(uint256 x, uint8 y) internal pure returns (uint256 z) {

contracts/libraries/SafeCast.sol

@@ -7,11 +7,13 @@ library SafeCast {
     }
 
     function toUint112(uint256 x) internal pure returns (uint112 y) {
-        require((y = uint112(x)) == x);
+        require(x <= type(uint112).max);
+        y = uint112(x);
     }
 
     function toUint128(uint256 x) internal pure returns (uint128 y) {
-        require((y = uint128(x)) == x);
+        require(x <= type(uint128).max);
+        y = uint128(x);
     }
 
     function truncateUint112(uint256 x) internal pure returns (uint112 y) {

contracts/libraries/WithdrawMath.sol

@@ -30,7 +30,7 @@ library WithdrawMath {
     {
         if (state.reserves.asset >= state.totalClaims.bond) return collateralOut;
         uint256 deficit = state.totalClaims.bond;
-        deficit -= state.reserves.asset;
+        unchecked { deficit -= state.reserves.asset; }
         if (uint256(state.reserves.collateral) * state.totalClaims.bond >= deficit * state.totalClaims.insurance) {
             uint256 _collateralOut = deficit;
             _collateralOut *= insuranceIn;