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code-423n4 / 2022-04-phuture-findings

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Gas Optimizations #7

Open code423n4 opened 2 years ago

code423n4 commented 2 years ago

1. Split up require statements instead of &&

Impact

Combining require statement conditions with && logic uses unnecessary gas. It is better to split up each part of the logical statement into separate require statements

Proof of Concept

Several instances of this issue was found https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/ChainlinkPriceOracle.sol#L51 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/ChainlinkPriceOracle.sol#L86 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/ManagedIndexReweightingLogic.sol#L30-L31 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/UniswapV2PriceOracle.sol#L46

Tools Used

Manual analysis

Recommended Mitigation Steps

Use separate require statements instead of concatenating with &&

2. Use prefix not postfix in loops

Impact

Using a prefix increment (++i) instead of a postfix increment (i++) saves gas for each loop cycle and so can have a big gas impact when the loop executes on a large number of elements.

Proof of Concept

There are three examples of this https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/UniswapV2PathPriceOracle.sol#L34 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/UniswapV2PathPriceOracle.sol#L49

Tools Used

Manual analysis

Recommended Mitigation Steps

Use prefix not postfix to increment in a loop

3. Short require strings save gas

Impact

Strings in solidity are handled in 32 byte chunks. A require string longer than 32 bytes uses more gas. Shortening these strings will save gas.

Proof of Concept

Several cases of this gas optimization were found. These are a few examples, but more may exist

  1. https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/UniswapV2PathPriceOracle.sol#L25
  2. https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/TopNMarketCapIndex.sol#L74
  3. https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/TopNMarketCapReweightingLogic.sol#L67

Tools Used

Manual analysis

Recommended Mitigation Steps

Shorten all require strings to less than 32 characters

4. Use != 0 instead of > 0

Impact

Using > 0 uses slightly more gas than using != 0. Use != 0 when comparing uint variables to zero, which cannot hold values below zero

Proof of Concept

Locations where this was found include https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/ManagedIndexReweightingLogic.sol#L56 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/ManagedIndexReweightingLogic.sol#L61 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/ManagedIndexReweightingLogic.sol#L98 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L76 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L86 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L98 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L114 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L141 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/PhutureIndex.sol#L56 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/PhutureIndex.sol#L64

Tools Used

grep

Recommended Mitigation Steps

Replace > 0 with != 0 to save gas

5. Cache array length before loop

Impact

Caching the array length outside a loop saves reading it on each iteration, as long as the array's length is not changed during the loop. This saves gas.

Proof of Concept

This optimization is already used in some places, but is not used in these places https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L39 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L60 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/IndexLogic.sol#L125 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/ManagedIndexReweightingLogic.sol#L38 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/TopNMarketCapReweightingLogic.sol#L37 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/TrackedIndexReweightingLogic.sol#L37 https://github.com/code-423n4/2022-04-phuture/blob/main/contracts/TrackedIndexReweightingLogic.sol#L66

Tools Used

Manual analysis

Recommended Mitigation Steps

Cache the array length before the for loop

jn-lp commented 2 years ago

Tips 2-5 were useful, thanks