OpenSea Seaport contest - 0x29A's results

Gas optimizations

Cache arrays length on loops

Caching the array length in memory can yield significant gas savings when the array length is high.

On file contracts/lib/OrderCombiner.sol you can cache the offers length and the consideration length;

diff --git a/contracts/lib/OrderCombiner.sol b/contracts/lib/OrderCombiner.sol
index babef49..6a5dd59 100644
--- a/contracts/lib/OrderCombiner.sol
+++ b/contracts/lib/OrderCombiner.sol
@@ -242,9 +242,10 @@ contract OrderCombiner is OrderFulfiller, FulfillmentApplier {
 
                 // Retrieve array of offer items for the order in question.
                 OfferItem[] memory offer = advancedOrder.parameters.offer;
-
+                // cache offer length
+                uint256 offerLength = offer.length;
                 // Iterate over each offer item on the order.
-                for (uint256 j = 0; j < offer.length; ++j) {
+                for (uint256 j = 0; j < offerLength; ++j) {
                     // Retrieve the offer item.
                     OfferItem memory offerItem = offer[j];
 
@@ -594,8 +595,9 @@ contract OrderCombiner is OrderFulfiller, FulfillmentApplier {
                     advancedOrder.parameters.consideration
                 );
 
+                uint256 considerationLength = consideration.length;
                 // Iterate over each consideration item to ensure it is met.
-                for (uint256 j = 0; j < consideration.length; ++j) {
+                for (uint256 j = 0; j < considerationLength; ++j) {
                     // Retrieve remaining amount on the consideration item.
                     uint256 unmetAmount = consideration[j].startAmount;

On file contracts/lib/OrderFulfiller.sol you can cache the offers length and the consideration length;

diff --git a/contracts/lib/OrderFulfiller.sol b/contracts/lib/OrderFulfiller.sol
index 0060ba9..3878254 100644
--- a/contracts/lib/OrderFulfiller.sol
+++ b/contracts/lib/OrderFulfiller.sol
@@ -214,7 +214,8 @@ contract OrderFulfiller is
             }
 
             // Iterate over each offer on the order.
-            for (uint256 i = 0; i < orderParameters.offer.length; ) {
+            uint256 totalOrderParameters = orderParameters.offer.length;
+            for (uint256 i = 0; i < totalOrderParameters; ) {
                 // Retrieve the offer item.
                 OfferItem memory offerItem = orderParameters.offer[i];

Use pre increment and pre decrement instead of post increment and post decrement

++i costs less gas compared to i++ or i += 1 for unsigned integers. This is because the pre-increment operation is cheaper. Source

diff --git a/contracts/lib/OrderCombiner.sol b/contracts/lib/OrderCombiner.sol
index babef49..915ed2f 100644
--- a/contracts/lib/OrderCombiner.sol
+++ b/contracts/lib/OrderCombiner.sol
@@ -226,7 +226,7 @@ contract OrderCombiner is OrderFulfiller, FulfillmentApplier {
                 orderHashes[i] = orderHash;
 
                 // Decrement the number of fulfilled orders.
-                maximumFulfilled--;
+                --maximumFulfilled;
 
                 // Place the start time for the order on the stack.
                 uint256 startTime = advancedOrder.parameters.startTime;
@@ -487,7 +487,7 @@ contract OrderCombiner is OrderFulfiller, FulfillmentApplier {
                 // If offerer and recipient on the execution are the same...
                 if (execution.item.recipient == execution.offerer) {
                     // increment total filtered executions.
-                    totalFilteredExecutions += 1;
+                    ++totalFilteredExecutions;
                 } else {
                     // Otherwise, assign the execution to the executions array.
                     executions[i - totalFilteredExecutions] = execution;
@@ -512,7 +512,7 @@ contract OrderCombiner is OrderFulfiller, FulfillmentApplier {
                 // If offerer and recipient on the execution are the same...
                 if (execution.item.recipient == execution.offerer) {
                     // increment total filtered executions.
-                    totalFilteredExecutions += 1;
+                    ++totalFilteredExecutions;
                 } else {
                     // Otherwise, assign the execution to the executions array.
                     executions[
@@ -765,7 +765,7 @@ contract OrderCombiner is OrderFulfiller, FulfillmentApplier {
                 // If offerer and recipient on the execution are the same...
                 if (execution.item.recipient == execution.offerer) {
                     // increment total filtered executions.
-                    totalFilteredExecutions += 1;
+                    ++totalFilteredExecutions;
                 } else {
                     // Otherwise, assign the execution to the executions array.
                     executions[i - totalFilteredExecutions] = execution;

Assembly casting of address/bytes32 to uint256

function toUint256(bytes32 value) internal pure returns (uint256 result) {
    assembly {
        result := value
    }
}

function toUint256(address value) internal pure returns (uint256 result) {
    assembly {
        result := value
    }
}

In ConduitController.sol

• L63(9 gas):

- if (address(uint160(bytes20(conduitKey))) != msg.sender) {
+ if (toUint256(conduitKey) != toUint256(msg.sender)) {

• L197(18 gas):

- if (newPotentialOwner == address(0)) {
+ if (toUint256(newPotentialOwner) == 0) {

• L237(13 gas):

- if (msg.sender != _conduits[conduit].potentialOwner) {
+ if (toUint256(msg.sender) != toUint256(_conduits[conduit].potentialOwner)) {

• L321-L334(13 gas):

conduit = address(
    uint160(
        uint256(
            keccak256(
                abi.encodePacked(
                    bytes1(0xff),
                    address(this),
                    conduitKey,
                    _CONDUIT_CREATION_CODE_HASH
                )
            )
        )
    )
);

- if (msg.sender != _conduits[conduit].potentialOwner) {
+ if (toUint256(msg.sender) != toUint256(_conduits[conduit].potentialOwner)) {

• L485(13 gas):

- if (msg.sender != _conduits[conduit].owner) {
+ if (toUint256(msg.sender) != toUint256(_conduits[conduit].owner)) {

In OrderValidator.sol, L280(18-36 gas):

- if (msg.sender != offerer && msg.sender != zone) {
+ if (toUint256(msg.sender) != toUint256(offerer) && toUint256(msg.sender) != toUint256(zone)) {

In SignatureVerification.sol, L97(18 gas):

- } else if (recoveredSigner != signer) {
+ } else if (toUint256(recoveredSigner) != toUint256(signer)) {

In ZoneInteraction.sol

• L48-L49, (18-36 gas):

- msg.sender != zone &&
- msg.sender != offerer
+ toUint256(msg.sender) != toUint256(zone) &&
+ toUint256(msg.sender) != toUint256(offerer)

• L117-L118, (18-36 gas):

- msg.sender != zone &&
- msg.sender != offerer
+ toUint256(msg.sender) != toUint256(zone) &&
+ toUint256(msg.sender) != toUint256(offerer)

In Verifiers.sol, L76(18 gas):

- if (offerer == msg.sender) {
+ if (toUint256(offerer) == toUint256(msg.sender)) {