Gas Optimizations

Summary Of Findings:

	Issue
1	Optimizing for loop's in `mintLegendaryGobbler` and `revealGobblers` method
2	Cache state variable in `legendaryGobblerPrice()` method
3	Optimizing formula in `mintReservedGobblers` method

Detailed Report on Gas Optimization Findings:

1. Optimizing for loop's in `mintLegendaryGobbler` and `revealGobblers` method

The mintLegendaryGobbler function in ArtGobblers.sol can save gas by modifying the for loop in the following way:

The following diff shows the mitigation:

diff --git "a/.\\orig.txt" "b/.\\modified.txt"
index 1d26328..a09619f 100644
--- "a/.\\orig.txt"
+++ "b/.\\modified.txt"
@@ -429,7 +429,9 @@ contract ArtGobblers is GobblersERC721, LogisticVRGDA, Owned, ERC1155TokenReceiv

             uint256 id; // Storing outside the loop saves ~7 gas per iteration.

-            for (uint256 i = 0; i < cost; ++i) {
+            for (uint256 i = 0; ; ++i) {
+       if(i == cost) break;  //gas saving here.
+
                 id = gobblerIds[i];

                 if (id >= FIRST_LEGENDARY_GOBBLER_ID) revert CannotBurnLegendary(id);

The forge gas report shows an average saving of 36 (72774 - 72738) and a maximum saving of 168 (456707 - 456539) from this single change.

The same kind of change could be made in the for loop in the revealGobblers function as well. The diff information shows the exact change:

diff --git "a/.\\orig.txt" "b/.\\modified.txt"
index 1d26328..f755227 100644
--- "a/.\\orig.txt"
+++ "b/.\\modified.txt"
@@ -589,7 +589,8 @@ contract ArtGobblers is GobblersERC721, LogisticVRGDA, Owned, ERC1155TokenReceiv
         // Implements a Knuth shuffle. If something in
         // here can overflow, we've got bigger problems.
         unchecked {
-            for (uint256 i = 0; i < numGobblers; ++i) {
+            for (uint256 i = 0; ; ++i) {
+       if(i == numGobblers) break;
                 /*//////////////////////////////////////////////////////////////
                                       DETERMINE RANDOM SWAP
                 //////////////////////////////////////////////////////////////*/

The forge gas report shows an average saving of 64 (525805 - 525741) and a maximum saving of 303 (2907828 - 2907525) gas for the revealGobblers function from this single change.

2. Cache state variable in `legendaryGobblerPrice()` method

The legendaryGobblerPrice function in ArtGobblers.sol can save gas by using the cached state variable in one of the formulas. The diff below shows the change.

diff --git "a/.\\orig.txt" "b/.\\modified.txt"
index 1d26328..39f7a95 100644
--- "a/.\\orig.txt"
+++ "b/.\\modified.txt"
@@ -490,7 +490,7 @@ contract ArtGobblers is GobblersERC721, LogisticVRGDA, Owned, ERC1155TokenReceiv
             if (numMintedAtStart > mintedFromGoo) revert LegendaryAuctionNotStarted(numMintedAtStart - mintedFromGoo);

             // Compute how many gobblers were minted since the auction began.
-            uint256 numMintedSinceStart = numMintedFromGoo - numMintedAtStart;
+            uint256 numMintedSinceStart = mintedFromGoo - numMintedAtStart;

             // prettier-ignore
             // If we've minted the full interval or beyond it, the price has decayed to 0.

The forge gas report shows an average saving of 109 (1646 - 1537) gas for legendaryGobblerPrice function from this single change.

3. Optimizing formula in `mintReservedGobblers` method

The mintReservedGobblers function in ArtGobblers.sol can save gas by modifying one of the formulas. The diff below shows the change.

diff --git "a/.\\orig.txt" "b/.\\modified.txt"
index 1d26328..2e5a111 100644
--- "a/.\\orig.txt"
+++ "b/.\\modified.txt"
@@ -841,7 +841,7 @@ contract ArtGobblers is GobblersERC721, LogisticVRGDA, Owned, ERC1155TokenReceiv
             // Optimistically increment numMintedForReserves, may be reverted below. Overflow in this
             // calculation is possible but numGobblersEach would have to be so large that it would cause the
             // loop in _batchMint to run out of gas quickly. Shift left by 1 is equivalent to multiplying by 2.
-            uint256 newNumMintedForReserves = numMintedForReserves += (numGobblersEach << 1);
+            uint256 newNumMintedForReserves = numMintedForReserves += (numGobblersEach + numGobblersEach);

             // Ensure that after this mint gobblers minted to reserves won't comprise more than 20% of
             // the sum of the supply of goo minted gobblers and the supply of gobblers minted to reserves.

The forge gas report shows an average saving of 3 gas (65982 - 65979) from this single change.

Conclusions:

	Issue	Max Gas Saved
1	Optimizing for loop in `mintLegendaryGobbler` method	168
2	Optimizing for loop in `revealGobblers` method	303
3	Cache state variable in `legendaryGobblerPrice()` method	109
4	Optimizing formula in `mintReservedGobblers` method	3

code-423n4 / 2022-09-artgobblers-findings