Use temporary variable for array.length

[code423n4]

Handle

PPrieditis

Vulnerability details

Impact

You are paying 100 gas (SSLOAD_COLD - COLD-READ) every time you read array.length from storage.

You can't avoid reading from storage once, but each subsequent read can be done via a supporting memory variable, this will cost 3 extra gas for storing, and just 3 gas for each time the value is read.

The same issue but for different contest: code-423n4/2021-10-union-findings#92

Recommended Mitigation Steps

Use local variable for array.length if value is necessary more than once.

Below is a list of places where .length is used in a loop:
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXLPStaking.sol#L206
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L297
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L379
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L399
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L414
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L437
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXStakingZap.sol#L192
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXStakingZap.sol#L203

Below is a list of places where .length is used more than once:
--- NFTXMarketplaceZap.sol: function buyAndSwap1155WETH()
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L303
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L304
--- NFTXMarketplaceZap.sol: function buyAndRedeem()
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L327
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L328
--- NFTXMarketplaceZap.sol: function buyAndRedeemWETH()
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L353
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXMarketplaceZap.sol#L354
--- NFTXStakingZap.sol: function provideInventory721()
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXStakingZap.sol#L185
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXStakingZap.sol#L192
--- NFTXVaultUpgradeable.sol: function redeemTo()
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L227
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L231
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L239
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L240
--- NFTXVaultUpgradeable.sol: function swapTo()
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L267
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L273
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L277
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L281
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L285
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L286
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L406
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L419
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L430
https://github.com/code-423n4/2021-12-nftx/blob/main/nftx-protocol-v2/contracts/solidity/NFTXVaultUpgradeable.sol#L444

[dmvt]

duplicate #198