Holograph contest - Saintcode_'s results

USE CALLDATA INSTEAD OF MEMORY

When a function with a memory array is called externally, the abi.decode() step has to use a for-loop to copy each index of the calldata to the memory index. Each iteration of this for-loop costs at least 60 gas (i.e. 60 * <mem_array>.length). Using calldata directly, obliviates the need for such a loop in the contract code and runtime execution.

When arguments are read-only on external functions, the data location should be calldata Instances: -Holographer.sol lines 147, 218 -HolographERC20.sol lines 499, 524, 641 -HolographERC721 llines 238, 456, 620

<ARRAY>.LENGTH SHOULD NOT BE LOOKED UP IN EVERY LOOP OF A FOR-LOOP

Reading array length at each iteration of the loop consumes more gas than necessary. In the best case scenario (length read on a memory variable), caching the array length in the stack saves around 3 gas per iteration. In the worst case scenario (external calls at each iteration), the amount of gas wasted can be massive.

Consider storing the array’s length in a variable before the for-loop, and use this new variable instead

Instances: -HolographOperator.sol line 871 -HolographERC20.sol line 564 -PA1D.sol lines 432, 437, 454, 474

<X> += <Y> COSTS MORE GAS THAN <X> = <X> + <Y> FOR STATE VARIABLES

Instances: -HolographOperator.sol lines 378, 382, 834 -HolographERC20.sol lines 685, 686, 702, 633

++I INSTEAD OF I++ (OR USE ASSEMBLY WHEN APPLICABLE)

Use ++i instead of i++. This is especially useful in for loops but this optimization can be used anywhere in your code.

Instances: -HolographOperator.sol lines 781, 871 -HolographERC20.sol lines 564, 713 -HolographERC721.sol lines 357, 716, 779 -PA1D.sol lines 307, 323, 340, 356, 394, 414, 432, 437, 454, 474

USE MULTIPLE REQUIRE() STATMENTS INSTEAD OF REQUIRE(EXPRESSION && EXPRESSION && ...)

Instances: -Holographer.sol line 166 -HolographERC721.sol line 464

IT COSTS MORE GAS TO INITIALIZE VARIABLES WITH THEIR DEFAULT VALUE THAN LETTING THE DEFAULT VALUE BE APPLIED

If a variable is not set/initialized, it is assumed to have the default value (0 for uint, false for bool, address(0) for address…). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

As an example: for (uint256 i = 0; i < numIterations; ++i) { should be replaced with for (uint256 i; i < numIterations; ++i) {

Instances: -HolographBridge.sol lines 380, 310, 311, 781 -HolographERC721.sol line 357, 716 -PA1D.sol lines 307, 323, 340, 356, 394, 414, 432, 437, 454, 474

>= COSTS LESS GAS THAN >

The compiler uses opcodes GT and ISZERO for solidity code that uses >, but only requires LT for >=, which saves 3 gas

Instances: -HolographBridge line 218 in this case is cheaper to use hTokenValue >= 1 -HolographOperator.sol lines 309, 350, 363, 393, 519, 1126 -HolographERC712.sol lines 815

++I/I++ SHOULD BE UNCHECKED{++I}/UNCHECKED{I++} WHEN IT IS NOT POSSIBLE FOR THEM TO OVERFLOW, AS IS THE CASE WHEN USED IN FOR- AND WHILE-LOOPS

The unchecked keyword is new in solidity version 0.8.0, so this only applies to that version or higher, which these instances are. This saves 30-40 gas per loop for (uint256 i = 0; i < orders.length; /** NOTE: Removed i++ **/ ) { // Do the thing // Unchecked pre-increment is cheapest unchecked { ++i; } }

Instances: -HolographOperator.sol lines 781, 871 -HolographERC20.sol lines 564 -HolographERC721.sol lines 357, 716, 779 -PA1D.sol lines 307, 323, 340, 356, 394, 414, 432, 437, 454, 474

USE CUSTOM ERRORS RATHER THAN REVERT()/REQUIRE() STRINGS TO SAVE GAS

Custom errors are available from solidity version 0.8.4. Custom errors save ~50 gas each time they’re hitby avoiding having to allocate and store the revert string. Not defining the strings also save deployment gas