1. New Modifier:
   Apply this modifier to these functions: addToPool(), removeFromPool(), updateMaxLoanRatio(), updateInterestRate().

   modifier callerIsLender(address lender) {

   require(lender == msg.sender, "Unauthorized");

   _;

   }

2. New Private Helper Functions:

   Define the following functions in Lender.sol and use them in the following lines:

   At lines 369 and 613 implement a new function called checkSameTokens():

   function checkSameTokens(Pool memory pool, Loan memory loan) private pure {

   if (pool.loanToken != loan.loanToken) revert TokenMismatch();

   if (pool.collateralToken != loan.collateralToken) {

   revert TokenMismatch();

   }

   }

   At lines 242 and 616 implement a new function called checkDebtSizeInPool():

   function checkDebtSizeInPool(Pool memory pool, uint256 debt) private pure {

   if (debt < pool.minLoanSize) revert LoanTooSmall();

   if (debt > pool.poolBalance) revert LoanTooLarge();

   }

   At lines 246, 384 and 619 implement a new function called calculateAndCheckValidLoanRatio():

   function calculateAndCheckValidLoanRatio(Pool memory pool, uint256 debt, uint256 collateral) private pure {

   uint256 loanRatio = (debt * 10 ** 18) / collateral;

   if (loanRatio > pool.maxLoanRatio) revert RatioTooHigh();

   }

3. Adjustment in refinance():
   Line 595.

   Replace the keccak256 encoding to get the pool ID for the already existing getPoolId() function.

   bytes32 oldPoolId = getPoolId(loans[loanId].lender, loans[loanId].loanToken, loans[loanId].collateralToken);

Test by test breakdown 🧑‍🔬

🚧 Note ⚠️: All tests but LenderTest:test_createPool have been included due to gas consumption changes being detected on them.

Test Name	Optimized Gas	Original Gas	Gas Saved
LenderTest:test_startAuction	626,592	626,519	-73
LenderTest:testFuzz_buyLoan	822,547	822,978	431
LenderTest:testFuzz_repay	509,976	509,918	-58
LenderTest:testFail_borrowTooLarge	246,285	246,264	-21
LenderTest:test_borrow	616,362	616,289	-73
LenderTest:testFuzz_seize	603,516	604,712	1,196
LenderTest:testFuzz_borrow	247,726	247,705	-21
LenderTest:test_giveLoan	854,193	853,996	-197
LenderTest:test_seize	546,648	546,589	-59
LenderTest:testFuzz_refinance	808,686	808,483	-203
LenderTest:testFail_repayNoTokens	617,851	617,778	-73
LenderTest:testFail_buyLoanTooLate	834,746	834,673	-73
LenderTest:testFail_buyLoanRateTooHigh	835,244	835,171	-73
LenderTest:test_repay	523,992	523,934	-58
LenderTest:test_buyLoan	857,779	857,706	-73
LenderTest:testFuzz_createPool	102,898	104,646	1,748
LenderTest:testFail_borrowTooSmall	246,349	246,328	-21
LenderTest:test_refinance	850,486	850,199	-287
LenderTest:testFail_startAuction	621,961	621,888	-73
LenderTest:testFail_seizeTooEarly	632,373	632,300	-73
LenderTest:test_interest	622,282	622,209	-73
TOTAL	12,382,620	12,389,631	1,793

Total saved percentage => 0.01%.

📘 Notice ℹ️: The percentage has been calculated with these numbers from the TOTAL:

( 1,793 / 12,389,631 ) * 100

They mean:

(totalGasSaved / originalGasCost) * 100

Forge Snapshots Used 📸

Original

LenderTest:testFail_borrowTooLarge() (gas: 246264)

LenderTest:testFail_borrowTooSmall() (gas: 246328)

LenderTest:testFail_buyLoanRateTooHigh() (gas: 835171)

LenderTest:testFail_buyLoanTooLate() (gas: 834673)

LenderTest:testFail_repayNoTokens() (gas: 617778)

LenderTest:testFail_seizeTooEarly() (gas: 632300)

LenderTest:testFail_startAuction() (gas: 621888)

LenderTest:testFuzz_borrow(uint256,uint256) (runs: 256, μ: 247705, ~: 247702)

LenderTest:testFuzz_buyLoan(uint256) (runs: 256, μ: 822978, ~: 833057)

LenderTest:testFuzz_createPool(uint256,uint256) (runs: 256, μ: 104646, ~: 22504)

LenderTest:testFuzz_refinance(uint256,uint256) (runs: 256, μ: 808483, ~: 808483)

LenderTest:testFuzz_repay(uint256) (runs: 256, μ: 509918, ~: 509917)

LenderTest:testFuzz_seize(uint256) (runs: 256, μ: 604712, ~: 605664)

LenderTest:test_borrow() (gas: 616289)

LenderTest:test_buyLoan() (gas: 857706)

LenderTest:test_createPool() (gas: 240654)

LenderTest:test_giveLoan() (gas: 853996)

LenderTest:test_interest() (gas: 622209)

LenderTest:test_refinance() (gas: 850199)

LenderTest:test_repay() (gas: 523934)

LenderTest:test_seize() (gas: 546589)

LenderTest:test_startAuction() (gas: 626519)

Optimized

LenderTest:test_startAuction | 626592 | 626519 | -73

LenderTest:testFuzz_buyLoan | 822547 | 822978 | 431

LenderTest:testFuzz_repay | 509976 | 509918 | -58

LenderTest:testFail_borrowTooLarge | 246285 | 246264 | -21

LenderTest:test_borrow | 616362 | 616289 | -73

LenderTest:testFuzz_seize | 603516 | 604712 | 1196

LenderTest:testFuzz_borrow | 247726 | 247705 | -21

LenderTest:test_giveLoan | 854193 | 853996 | -197

LenderTest:test_seize | 546648 | 546589 | -59

LenderTest:test_createPool | 240654 | 240654 | 0

LenderTest:testFuzz_refinance | 808686 | 808483 | -203

LenderTest:testFail_repayNoTokens | 617851 | 617778 | -73

LenderTest:testFail_buyLoanTooLate | 834746 | 834673 | -73

LenderTest:testFail_buyLoanRateTooHigh | 835244 | 835171 | -73

LenderTest:test_repay | 523992 | 523934 | -58

LenderTest:test_buyLoan | 857779 | 857706 | -73

LenderTest:testFuzz_createPool | 102898 | 104646 | 1748

LenderTest:testFail_borrowTooSmall | 246349 | 246328 | -21

LenderTest:test_refinance | 850486 | 850199 | -287

LenderTest:testFail_startAuction | 621961 | 621888 | -73

LenderTest:testFail_seizeTooEarly | 632373 | 632300 | -73

LenderTest:test_interest | 622282 | 622209 | -73

🚧 Note ⚠️: The figures presented represent total gas consumption. Not every individual modification necessarily contributes to gas savings. Some changes might increase gas costs, while others decrease them. However, the net effect can still result in overall reduced gas consumption. To fully understand the impact of each change, a more detailed, granular analysis is essential for each modification.