57663 sc insight gas storage optimization erc1155info struct in structures sol can save one slot through field reordering

• Submitted on: Oct 27th 2025 at 23:19:41 UTC by @chief_hunter888 for Audit Comp | Belong

• Report ID: #57663

• Report Type: Smart Contract

• Report severity: Insight

• Target: https://github.com/immunefi-team/audit-comp-belong/blob/main/contracts/v2/Structures.sol

Description

Brief Summary

The Structures.sol file defines multiple custom data structures (AccessTokenInfo, ERC1155Info, CustomerInfo, PromoterInfo, etc.) that contain a mix of fields: address, bool, and smaller integer types (uint96, uint128, uint24, etc.).

Problem: In the Structures.sol struct layout, several structs are not optimally packed for efficient storage utilisation, resulting in unnecessary consumption of additional 32-byte storage slots. This increases gas cost for storing these structs. Solidity packs contiguous smaller types (<32 bytes) together if adjacent in declaration order and combined size ≤ 32 bytes. Dynamic types and large types (address, uint256, string, bytes, mapping) start a new slot.

Solution: Move the bool transferable in ERC1155Info next to the static fields (addresses) so it can be packed into an existing slot rather than occupying its own slot. This reduces the number of storage slots used per ERC1155Info struct from 8 to 7, saving one 32-byte slot (≈ ~20,000 gas on initial write).

Context: Solidity Storage Basics - How to Optimize Solidity Storage

Each storage slot = 32 bytes (256 bits). Solidity packs contiguous smaller types (<32 bytes) together into the same slot if:

• They are adjacent in declaration order.

• Their combined size ≤ 32 bytes.

Group smaller types together before introducing larger ones (address, uint256, string, bytes, mapping, etc. always start a new slot).

Below are the relevant structs and the suggested reordering for ERC1155Info.

---

3. ERC1155Info

Current declaration in Structures.sol:

struct ERC1155Info {
    string name;
    string symbol;
    address defaultAdmin;
    address manager;
    address minter;
    address burner;
    string uri;
    bool transferable;
}

Improvement Suggestion

Dynamic fields (string) always occupy their own slots, so packing is limited. The bool transferable could be grouped before the dynamic fields (string) to share a slot with address burner (or any adjacent address). Reorder to place bool transferable adjacent to the addresses so it fits into the remaining bytes of an address slot instead of forcing a new slot.

Suggested optimized layout:

struct ERC1155Info {
    string name;
    string symbol;
    address defaultAdmin;
    bool transferable;
    address manager;
    address minter;
    address burner;
    string uri;
}

Rationale: The four addresses (4 × 20 bytes = 80 bytes) still occupy four slots, but the bool (1 byte) can now be packed into the slot containing an address, saving one full slot compared to the original layout where the bool was declared after dynamic fields and forced into its own slot.

✅ Saves 1 storage slot vs current layout.

---

ERC1155Info Finding Summary Details

Finding: The struct ERC1155Info — Can save 1 storage slot

Current Layout (rough):

• Slot 1-2: string name, string symbol (dynamic)

• Slot 3: address defaultAdmin (20 bytes) → 12 bytes wasted

• Slot 4: address manager (20 bytes) → 12 bytes wasted

• Slot 5: address minter (20 bytes) → 12 bytes wasted

• Slot 6: address burner (20 bytes) → 12 bytes wasted

• Slot 7+: string uri (dynamic)

• Slot 8+: bool transferable (1 byte) → 31 bytes wasted

Optimized: Move bool transferable next to any address to pack them together (20 + 1 = 21 bytes in one slot).

Improved storage layout (example):

• Slot 1-2: string name, string symbol (dynamic)

• Slot 3: address defaultAdmin (20 bytes) + bool (1 byte) → 11 bytes wasted

• Slot 4: address manager (20 bytes) → 12 bytes wasted

• Slot 5: address minter (20 bytes) → 12 bytes wasted

• Slot 6: address burner (20 bytes) → 12 bytes wasted

• Slot 7+: string uri (dynamic)

One full slot saved.

Example docstring for the optimized struct:

/// @title ERC1155Info
/// @notice Initialization/configuration data for a CreditToken (ERC-1155) collection.
struct ERC1155Info {
    string name;
    string symbol;
    address defaultAdmin;
    bool transferable;
    address manager;
    address minter;
    address burner;
    string uri;
}

---

Summary of Potential Storage Improvements

Struct	Slots Saved (Est.)	Change
NftMetadata	0	optimal
AccessTokenInfo	0	Optimal
ERC1155Info	1 slot	Move bool above dynamic fields
VestingWalletInfo	0	Optimal
StaticPriceParameters	0	Optimal
DynamicPriceParameters	0	Optimal
VenueRules	0	Optimal
VenueInfo	0	Optimal
CustomerInfo	0	Optimal
PromoterInfo	0	Optimal

---

Impact Details

Reordering the fields of ERC1155Info achieves a saving of one 32-byte storage slot. Each eliminated slot corresponds to a reduction of approximately:

• ~20,000 gas when first written (cold SSTORE), and

• ~5,000 gas for subsequent updates (warm writes differ depending on state transitions and EVM specifics).

This improvement is non-invasive, requires no logic changes, and directly enhances contract performance for storage-heavy operations (deployments, updates to these structs, or repeated writes).

---

Proof of Concept

The optimized Structures.sol file (showing the adjusted ERC1155Info and full file for context):

// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.8.27;

struct NftMetadata {
    /// @notice The name of the NFT collection.
    string name;
    /// @notice The symbol representing the NFT collection.
    string symbol;
}

/// @title AccessTokenInfo
/// @notice Initialization/configuration data for an AccessToken (ERC-721) collection.
/// @dev
/// - `paymentToken` can be a token address or the NativeCurrency pseudo-address
///   (0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE).
/// - `feeNumerator` is used for ERC-2981 royalty configuration.
/// - `signature` is validated off-chain by a platform signer.
struct AccessTokenInfo {
    /// @notice ERC-20 used for payments, or NativeCurrency pseudo-address for native NativeCurrency.
    address paymentToken;
    /// @notice ERC-2981 royalty numerator (denominator defined by receiver).
    uint96 feeNumerator;
    /// @notice Whether transfers between users are allowed.
    bool transferable;
    /// @notice Collection-wide supply cap.
    uint256 maxTotalSupply;
    /// @notice Public mint price.
    uint256 mintPrice;
    /// @notice Whitelist mint price.
    uint256 whitelistMintPrice;
    /// @notice Optional collection expiration timestamp (seconds since epoch).
    uint256 collectionExpire;
    /// @notice Collection name and symbol stored as NftMetadata struct.
    NftMetadata metadata;
    /// @notice Contract-level metadata URI.
    string contractURI;
    /// @notice Backend signature authorizing creation with the provided fields.
    bytes signature;
}

/// @title ERC1155Info
/// @notice Initialization/configuration data for a CreditToken (ERC-1155) collection.
struct ERC1155Info {
    string name;
    string symbol;
    address defaultAdmin;
    bool transferable;
    address manager;
    address minter;
    address burner;
    string uri;
}

/// @title VestingWalletInfo
/// @notice Parameters configuring a vesting wallet schedule and metadata.
struct VestingWalletInfo {
    /// @notice Vesting start timestamp (TGE) in seconds since epoch.
    uint64 startTimestamp;
    /// @notice Cliff duration in seconds added to `startTimestamp` for the linear section to begin.
    uint64 cliffDurationSeconds;
    /// @notice Linear vesting duration in seconds counted from `cliff`.
    uint64 durationSeconds;
    /// @notice ERC-20 token being vested.
    address token;
    /// @notice Recipient of vested token releases.
    address beneficiary;
    /// @notice Total tokens allocated to this vesting schedule (must equal TGE + linear + tranches).
    uint256 totalAllocation;
    /// @notice One-off amount vested immediately at `startTimestamp`.
    uint256 tgeAmount;
    /// @notice Amount linearly vested over `durationSeconds` starting at `cliff`.
    uint256 linearAllocation;
    /// @notice Human-readable description of the vesting schedule.
    string description;
}

/// @title StaticPriceParameters
/// @notice Mint payload for static-priced mints validated by a platform signer.
struct StaticPriceParameters {
    /// @notice Token id to mint.
    uint256 tokenId;
    /// @notice Whether receiver is eligible for whitelist pricing.
    bool whitelisted;
    /// @notice Token metadata URI.
    string tokenUri;
    /// @notice Backend signature validating the payload.
    bytes signature;
}

/// @title DynamicPriceParameters
/// @notice Mint payload for dynamic-priced mints validated by a platform signer.
struct DynamicPriceParameters {
    /// @notice Token id to mint.
    uint256 tokenId;
    /// @notice Explicit price for this mint.
    uint256 price;
    /// @notice Token metadata URI.
    string tokenUri;
    /// @notice Backend signature validating the payload.
    bytes signature;
}

/// @title StakingTiers
/// @notice Tier levels derived from staked LONG balance.
enum StakingTiers {
    NoStakes,
    BronzeTier,
    SilverTier,
    GoldTier,
    PlatinumTier
}

/// @title PaymentTypes
/// @notice Venue-allowed payment currencies.
enum PaymentTypes {
    NoType,
    USDC,
    LONG,
    Both
}

/// @title BountyTypes
/// @notice Venue-allowed promoter bounty schemes.
enum BountyTypes {
    NoType,
    VisitBounty,
    SpendBounty,
    Both
}

/// @title LongPaymentTypes
/// @notice Venue-allowed Long payment options.
enum LongPaymentTypes {
    NoType,
    AutoStake,
    AutoConvert
}

/// @title VenueRules
/// @notice Venue-level configuration for payment and bounty types.
struct VenueRules {
    PaymentTypes paymentType;
    BountyTypes bountyType;
    LongPaymentTypes longPaymentType;
}

/// @title VenueInfo
/// @notice Signed payload authorizing a venue deposit and metadata update.
struct VenueInfo {
    VenueRules rules;
    address venue;
    uint256 amount;
    bytes32 referralCode;
    string uri;
    bytes signature;
}

/// @title CustomerInfo
/// @notice Signed payload authorizing a customer payment to a venue (and optional promoter attribution).
struct CustomerInfo {
    // Backend configurable
    bool paymentInUSDC;
    uint128 visitBountyAmount;
    uint24 spendBountyPercentage;
    // Actors
    address customer;
    address venueToPayFor;
    address promoter;
    // Amounts
    uint256 amount;
    bytes signature;
}

/// @title PromoterInfo
/// @notice Signed payload authorizing distribution of promoter payouts in USDC or LONG.
struct PromoterInfo {
    bool paymentInUSDC;
    address venue;
    uint256 amountInUSD;
    bytes signature;
}

---

Summary

• Reordering bool transferable to sit next to address fields in ERC1155Info saves one storage slot per struct instance.

• This is a low-risk, non-functional change that reduces gas cost for writes and updates related to ERC1155Info.

• No logic changes required — only declaration order adjustment to improve packing.