Nouns Builder 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. Operatos <= or >= cost more gas than operators < or >
4. != 0 is cheaper than > 0
5. Variable1 = Variable1 + (-) Variable2 is cheaper in gas cost than variable1 += (-=) variable2.
6. Using private rather than public for constants, saves gas
7. Using bools for storage incurs overhead
8. ABI.ENCODE() is less efficient than ABI.ENCODEPACKED()
9. Multiplication/division by two should use bit shifting

Details

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

Description

++I (--I) cost less gas than I++ (I--) especially in a loop.

Proof of concept

contract TestPost {
	function testPost() public {
		uint256 i;
		i++;
	}
}
contract TestPre {
	function testPre() public {
		uint256 i;
		++i;
	}
}

• Transaction cost of testPost is 21333 gas
• Transaction cost of testPre is 21328 gas
• After the test it's possible to save 5 gas per ocurrence with this optimization.

Lines in the code

Token.sol#L91 Token.sol#L154 Governor.sol#L230 ERC721Votes.sol#L162 ERC721Votes.sol#L207 ERC721Votes.sol#L222

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

Governor.sol#L27 ERC721Votes.sol#L21 EIP712.sol#L19

3. 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)

Proof of concept

contract TestMaxEqual {

	function testMaxEqual() public {
		uint256 i = 1;
		if (i >= 1){
			i++;
		}
	}
}

contract TestMax {

	function TestMax() public {
		uint256 i = 1;
		if (i > 0){
			i++;
		}
	}
}

• Transaction cost of TestMaxEqual is 21367 gas
• Transaction cost of TestMax is 21364 gas
• After the test it's possible to save 3 gas per ocurrence with this optimization.

Lines in the code

Auction.sol#L98 Treasury.sol#L89 ERC721Votes.sol#L61 ERC721Votes.sol#L78 Initializable.sol#L56

4. != 0 is cheaper than > 0

Description

Replace all > 0 for != 0

Lines in the code

ERC1967Upgrade.sol#L61 ERC721Votes.sol#L203 Address.sol#L50

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

Lines in the code

Token.sol#L88 Token.sol#L118 Governor.sol#L280 Governor.sol#L285 Governor.sol#L290 MetadataRenderer.sol#L140

6. 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

Governor.sol#L27

7. 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

Auction.sol#L136 Auction.sol#L349 AuctionTypesV1.sol#L35 Treasury.sol#L164 Address.sol#L40 Initializable.sol#L20 Initializable.sol#L34 Pausable.sol#L15 MetadataRenderer.sol#L231 GovernorTypesV1.sol#L52 GovernorTypesV1.sol#L53 GovernorTypesV1.sol#L54 MetadataRendererTypesV1.sol#L11

8. ABI.ENCODE() is less efficient than ABI.ENCODEPACKED()

Lines in the code

Governor.sol#L104 Governor.sol#L230 Treasury.sol#L107 EIP712.sol#L69 MetadataRenderer.sol#L251 MetadataRenderer.sol#L309

9. Multiplication/division by two should use bit shifting

Description

<x> * 2 is equivalent to <x> << 1 and <x> / 2 is the same as <x> >> 1. The MUL and DIV opcodes cost 5 gas, whereas SHL and SHR only cost 3 gas

Lines in the code

ERC721Votes.sol#L95