ElasticSwap contest - sirhashalot's results

Handle

sirhashalot

Vulnerability details

Impact

The Exchange.sol removeLiquidity() function calls this.totalSupply() twice. To save gas, call it once and set the value to a variable, because using a variable is cheaper than a second function call.

Proof of Concept

There are two calls to this.totalSupply() in removeLiquidity()

Recommended Mitigation Steps

Move line 187, shown below, to a line before the require statement. Modify the require statement to reference the variable. The end result will look like:

uint256 totalSupplyOfLiquidityTokens = this.totalSupply();
require(totalSupplyOfLiquidityTokens > 0, "Exchange: INSUFFICIENT_LIQUIDITY");

Handle

sirhashalot

Vulnerability details

Impact

Strings are broken into 32 byte chunks for operations. Revert error strings over 32 bytes therefore consume extra gas as documented publicly

Proof of Concept

There are multiple examples of this gas optimization opportunity, including but not limited to:

• Exchange.sol line 137, line 179
• ExchangeFactory.sol line 75 (Warning: this require statement has a typo, the letter L should be uppercase)
• MathLib.sol line 337

Recommended Mitigation Steps

Reducing revert error strings to under 32 bytes decreases deployment time gas and runtime gas when the revert condition is met. Alternatively, the code could be modified to use custom errors, introduced in Solidity 0.8.4: https://blog.soliditylang.org/2021/04/21/custom-errors/