fix: gas optimization branch

[aaitor]

Description

The objective of this change would be to reduce the amount of gas used for the NFT1155Subscription contract, specially for the burn mechanism.

Is this PR related with an open issue?

Related to Issue #

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Follows the code style of this project.
• Tests Cover Changes
• Documentation

Funny gif

[aaitor]

current burn in v3.5.7:

[kupermind]

Try to squeeze the whole struct such that in summary its fields are <= 256 bits (aka uint256, 32 bytes or one slot). For example, the expirationBlock / mintBlock can be defined as uint64 as (for example, Arbitrum) is a bit faster than 2 blocks per second, and one might calculate for how long this value is safe.

As for the amountMinted, depending on the projected total supply and decimals, this might be bounded by uint96?

After these changes, we have uint64 + uint96 + uint64 + uint8 (bool) < uint256.

[aaitor]

The problem of that approach is would break compatibility with existing subscriptions minted. Probably this contract only could be upgraded adding a new mapping but existing subscriptions could not be burned anymore.

[kupermind]

@aaitor Couple of more things:

• Cache _msgSender() before using in multiple places, also try to cache anything that is read from storage, for further multiple usage;
• Get memory array from _tokens[_key] and loop over it. Also note, that you are pushing into the same _tokens[_key] array, and depending on how the compiler treats the _tokens[_key].length, you might parse elements that were just added.
• Think about the algorithm whether it's possible to reduce the loop size or pre-collect data / use maps?

[aaitor]

I pushed a new contract without the time expiration feature (so no track of expiring blocks needed). It comes with a significant reduction on gas cost:

In the test burn gas cost goes from Avg 129k to 64k with is the half.

This new contract NFT1155SubscriptionWithoutBlocks is adapted to the functionality you needed and don't include the overhead of the blocks control and storage.