Foundation Drop contest - ajtra's results

Index

1. Post-increment/decrement cost more gas then pre-increment/decrement
2. Call to KECCAK256 should use IMMUTABLE rather than constant
3. Array length should not be looked up in every loop of a for-loop
4. Operatos <= or >= cost more gas than operators < or >
5. != 0 is cheaper than > 0
6. Variable1 = Variable1 + (-) Variable2 is cheaper in gas cost than variable1 += (-=) variable2.
7. Use bytes32 instead of string
8. Require / Revert strings longer than 32 bytes cost extra gas
9. Use custom errors rather than REVERT()/REQUIRE() strings to save deployment gas
10. Using private rather than public for constants, saves gas
11. Initialize variables with default values are not needed
12. Using bools for storage incurs overhead
13. Uncheked arithmetic when it is not possible for them to overflow
14. Refactoring the code of NFTCollection._baseURI to save gas
15. Refactoring the code of BytesLibrary.startsWith to save gas

Details

1. Post-increment/decrement cost more gas then pre-increment/decrement

Description

++I (--I) cost less gas than I++ (I--)

Lines in the code

NFTCollectionFactory.sol#L207 NFTCollectionFactory.sol#L231

2. Call to KECCAK256 should use IMMUTABLE rather than constant

Description

Expressions for constant values such as a call to KECCAK256 should use IMMUTABLE rather than constant

Lines in the code

MinterRole.sol#L19 NFTDropMarketFixedPriceSale.sol#L70

3. Array length should not be looked up in every loop of a for-loop

Description

Storage array length checks incur an extra Gwarmaccess (100 gas) per loop. Store the array length in a variable and use it in the for loop helps to save gas

Lines in the code

MarketFees.sol#L126 MarketFees.sol#L198 MarketFees.sol#L484 MarketFees.sol#L503

4. Operatos <= or >= cost more gas than operators < or >

Description

Change all <= / >= operators for < / > and remember to increse / decrese in consecuence to maintain the logic (example, a <= b for a < b + 1)

Lines in the code

NFTCollection.sol#L268 NFTDropCollection.sol#L179 NFTDropCollection.sol#L181 NFTDropCollection.sol#L275 MarketFees.sol#L526 SequentialMintCollection.sol#L89 NFTDropMarketFixedPriceSale.sol#L240

5. != 0 is cheaper than > 0

Description

Replace all > 0 for != 0

Lines in the code

NFTDropCollection.sol#L88 NFTDropCollection.sol#L130 NFTDropCollection.sol#L131 MarketFees.sol#L244

6. Variable1 = Variable1 + (-) Variable2 is cheaper in gas cost than variable1 += (-=) variable2.

Description

Lines in the code

MarketFees.sol#L134 MarketFees.sol#L150 MarketFees.sol#L199 MarketFees.sol#L490 MarketFees.sol#L505 MarketFees.sol#L527

7. Use bytes32 instead of string

Description

Use bytes32 instead of string when it's possible to save some gas. In this project, it's probably that the symbol is not going to be bigger than 32 bytes so it's possible to change it from string to bytes32 to save some gas.

Lines in the code

NFTCollection.sol#L108 NFTCollectionFactory.sol#L138 NFTCollectionFactory.sol#L163 NFTCollectionFactory.sol#L259 NFTCollectionFactory.sol#L288 NFTCollectionFactory.sol#L326 NFTCollectionFactory.sol#L365 NFTCollectionFactory.sol#L388 NFTDropCollection.sol#L123

8. Require / Revert strings longer than 32 bytes cost extra gas

Description

Each extra memory word of bytes past the original 32 incurs an MSTORE which costs 3 gas

Lines in the code

NFTCollection.sol#L158 NFTCollection.sol#L263 NFTCollection.sol#L264 NFTCollection.sol#L268 NFTCollection.sol#L327 NFTCollectionFactory.sol#L173 NFTCollectionFactory.sol#L182 NFTCollectionFactory.sol#L203 NFTCollectionFactory.sol#L227 NFTCollectionFactory.sol#L262 NFTDropCollection.sol#L88 NFTDropCollection.sol#L93 NFTDropCollection.sol#L130 NFTDropCollection.sol#L131 NFTDropCollection.sol#L172 NFTDropCollection.sol#L179 NFTDropCollection.sol#L238 AddressLibrary.sol#L31 ContractFactory.sol#L22 ContractFactory.sol#L31 MinterRole.sol#L22 SequentialMintCollection.sol#L58 SequentialMintCollection.sol#L63 SequentialMintCollection.sol#L74 SequentialMintCollection.sol#L87 SequentialMintCollection.sol#L88 SequentialMintCollection.sol#L89 AdminRole.sol#L19

9. Use custom errors rather than REVERT()/REQUIRE() strings to save deployment gas

Description

Custom errors are available from solidity version 0.8.4. Custom errors save ~50 gas each time they’re hitby avoiding having to allocate and store the revert string. Not defining the strings also save deployment gas.

Lines in the code

NFTCollection.sol#L158 NFTCollection.sol#L263 NFTCollection.sol#L264 NFTCollection.sol#L268 NFTCollection.sol#L327 NFTCollectionFactory.sol#L173 NFTCollectionFactory.sol#L182 NFTCollectionFactory.sol#L203 NFTCollectionFactory.sol#L227 NFTCollectionFactory.sol#L262 NFTDropCollection.sol#L88 NFTDropCollection.sol#L93 NFTDropCollection.sol#L130 NFTDropCollection.sol#L131 NFTDropCollection.sol#L172 NFTDropCollection.sol#L179 NFTDropCollection.sol#L238 AddressLibrary.sol#L31 ContractFactory.sol#L22 ContractFactory.sol#L31 MinterRole.sol#L22 SequentialMintCollection.sol#L58 SequentialMintCollection.sol#L63 SequentialMintCollection.sol#L74 SequentialMintCollection.sol#L87 SequentialMintCollection.sol#L88 SequentialMintCollection.sol#L89 AdminRole.sol#L19

10. Using private rather than public for constants, saves gas

Description

If needed, the value can be read from the verified contract source code. Savings are due to the compiler not having to create non-payable getter functions for deployment calldata, and not adding another entry to the method ID table

Lines in the code

MinterRole.sol#L19 NFTDropMarketFixedPriceSale.sol#L70

11. Initialize variables with default values are not needed

Description

If a variable is not set/initialized, it is assumed to have the default value (0 for uint, false for bool, address(0) for address,...). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

Lines in the code

MarketFees.sol#L126 MarketFees.sol#L198 MarketFees.sol#L484 BytesLibrary.sol#L25 BytesLibrary.sol#L44

12. Using bools for storage incurs overhead

Description

Use uint256(1) and uint256(2) for true/false to avoid a Gwarmaccess (100 gas), and to avoid Gsset (20000 gas) when changing from 'false' to 'true', after having been 'true' in the past.

Lines in the code

NFTCollection.sol#L53 MarketFees.sol#L61 NFTDropMarketFixedPriceSale.sol#L232

13. Uncheked arithmetic when it is not possible for them to overflow

Description

The default “checked” behavior costs more gas when adding/diving/multiplying, because under-the-hood those checks are implemented as a series of opcodes that, prior to performing the actual arithmetic, check for under/overflow and revert if it is detected. if it can statically be determined there is no possible way for your arithmetic to under/overflow (such as a condition in an if statement), surrounding the arithmetic in an unchecked block will save gas.

For all for-loops in the code it is possible to change as the following example.

for (uint256 i;i < X;){ -- code -- unchecked { ++i; } }

Lines in the code

MarketFees.sol#L198

14. Refactoring the code of NFTCollection._baseURI to save gas

Description

In the case of _baseURI it's possible to refactor the code to save gas. 180 of gas is saved with the following change. (-) Remove the line (+) Add the line

  function _baseURI() internal view override returns (string memory) {
-   if (bytes(baseURI_).length != 0) {
-    return baseURI_;
-   }
-   return "ipfs://";
+	return (bytes(baseURI_).length != 0)?baseURI_:"ipfs://";
  }

Lines in the code

NFTCollection.sol#L332-L337

15. Refactoring the code of BytesLibrary.startsWith to save gas

Description

In the case of startsWith it's possible to refactor the code to save gas as the following way. 222 gas will be saved with this change. (-) Remove the line (+) Add the line

  function startsWith(bytes memory callData, bytes4 functionSig) internal pure returns (bool) {
    // A signature is 4 bytes long
-   if (callData.length < 4) {
-     return false;
-   }
-   unchecked {
-    for (uint256 i = 0; i < 4; ++i) {
-      if (callData[i] != functionSig[i]) {
-        return false;
-      }
-    }
-   }

-   return true;
+	return !(callData.length < 4 || callData[0] != functionSig[0]|| callData[1] != functionSig[1]|| callData[2] != functionSig[2]|| callData[3] != functionSig[3]);

  }

Lines in the code

BytesLibrary.sol#L38-L52

createNFTDropCollection gas reporter results:
  using > 0 (current):
    - 319246  ·     319578  ·      319361
  using != 0 (recommendation):
    -  319252  ·     319584  ·      319367
  impact: +6 gas