Forgotten Runes Warrior Guild contest - slywaters's results

Gas Report

Variables do not need to be initialized with 'empty' values such as 0, false, or address(0)

Uninitialized variables by default contain a value equivalent to 0: uints are initialized to 0; bools to false; addresses to address(0).

Explicitly assigning these values to variables when they are declared increases gas costs while providing no funciton.

e.g. change this code:

uint256 var = 0;

to

uint256 var;

For more information, please consult the following resources:

Tips and Tricks to Save Gas and Reduce Bytecode Size

The following lines of code are affected:

code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsGuild.sol:24:    uint256 public numMinted = 0;
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:162:        for (uint256 i = 0; i < numWarriors; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:220:        for (uint256 i = 0; i < numWarriors; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:259:        for (uint256 i = 0; i < count; i++) {

Unchecked increment can be used in for-loop

Newer versions of the Solidity compiler will check for integer overflows and underflows automatically. This provides safety but increases gas costs.

When an unsigned integer is guaranteed to never overflow, the unchecked feature of Solidity can be used to save gas costs.

A common case for this is for-loops using a strictly-less-than comparision in their conditional statement, e.g.:

uint256 length = someArray.length;
for (uint256 i; i < length; ++i) {
}

In cases like this, the maximum value for length is 2**256 - 1. Therefore, the maximum value of i is 2**256 - 2 as it will always be strictly less than length.

This example can be replaced with the following construction to reduce gas costs:

for (uint i = 0; i < length; i = unchecked_inc(i)) {
    // do something that doesn't change the value of i
}

function unchecked_inc(uint i) returns (uint) {
    unchecked {
        return i + 1;
    }
}

For more information, consult the following resources:

Solidity gas optimizations

Solidity docs: underflows, overflows, and unchecked

The following lines of code are affected:

code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:162:        for (uint256 i = 0; i < numWarriors; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:220:        for (uint256 i = 0; i < numWarriors; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:259:        for (uint256 i = 0; i < count; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:355:        for (uint256 i = startIdx; i < endIdx + 1; i++) {

Replace postfix increment (var++) with prefix increment (++var)

Using ++i costs less gas than using i++. In the context of a for-loop, gas is saved on each iteration.

The following lines of code are affected:

Replace strict greater-than-zero operation (> 0) with does-not-equal-zero (!= 0) operation

When checking whether a value is equal to zero, using the construction var != 0 is costs less gas than using var > 0. Note that this is true only when the comparison occurs in a conditional context and the Solidity compiler is using the Optimizer.

For more information, please consult the following resources:

Twitter discussion detailing the gas costs of != 0 vs > 0 in require() calls

Solidity Compiler: Optimizer options

The following lines of code are affected:

code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:162:        for (uint256 i = 0; i < numWarriors; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:220:        for (uint256 i = 0; i < numWarriors; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:259:        for (uint256 i = 0; i < count; i++) {
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:355:        for (uint256 i = startIdx; i < endIdx + 1; i++) {

Shorter require() messages can save gas costs

Revert message strings included in calls to require() are stored in 32-byte chunks when contracts are deployed. To optimize gas costs, consider using revert messages that are less than 32 bytes in length.

For more information, see the following resource: Gas optimization tips: Shorter revert strings

The following lines of code are affected:

code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsGuild.sol:70:          'ERC721Metadata: URI query for nonexistent token'
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:142:        'You can summon no more than 20 Warriors at a time'
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:148:        'Ether value sent is not sufficient'
code4rena/2022-05-runes/contracts/ForgottenRunesWarriorsMinter.sol:212:        'You can summon no more than 20 Warriors at a time'