Gas Optimizations

To prevent repeated code revision reverting, the following gas optimizations are done cumulatively, meaning each one adds to the last's codebase. These are also from running forge test --gas-report with a custom Foundry profile that limits fuzz runs to 100 and disables the IR pipeline.

1 - Use shr instead of dividing by 4

Replace the line here with:

route := shr(2, calldataload(BasicOrder_basicOrderType_cdPtr))

Saves on average 3 gas per fulfillBasicOrder() call according to tests. Saves 1 gas on median.

Before: fulfillBasicOrder ┆ 753 ┆ 578873 ┆ 214735 ┆ 3437148
After: fulfillBasicOrder ┆ 751 ┆ 578870 ┆ 214734 ┆ 3437146

2 - Short-Circuit a reverting inequality check

Replace the block starting here, copied below:

if (amount != 1) {
    revert InvalidERC721TransferAmount();
}

// Perform transfer via the token contract directly.
_performERC721Transfer(token, from, to, identifier);

With the following:

if (amount == 1) {
    // Perform transfer via the token contract directly.
    _performERC721Transfer(token, from, to, identifier);
} else {
    revert InvalidERC721TransferAmount();
}

This again saves extremely small amounts of gas on fulfillBasicOrder(), but hey, it's something.

Before: fulfillBasicOrder ┆ 751 ┆ 578870 ┆ 214734 ┆ 3437146
After: fulfillBasicOrder ┆ 751 ┆ 578870 ┆ 214733 ┆ 3437145

code-423n4 / 2022-05-opensea-seaport-findings