calculateErc8042

Calculate ERC-8042 diamond storage slot

calculateErc8042(keccak256: Function, id: string): Uint8Array

Calculates a storage slot using the ERC-8042 (Diamond Storage) formula: keccak256(id).

Simpler than ERC-7201, used primarily by the EIP-2535 Diamond Standard.

Parameters:

• keccak256: (data: Uint8Array) => Uint8Array - Keccak256 hash function
• id: string - Storage namespace identifier

Returns: Uint8Array - 32-byte storage slot

Example:

import { calculateErc8042 } from '@tevm/voltaire/Storage';
import { keccak256 } from '@tevm/voltaire/crypto';

// Calculate diamond storage slot
const slot = calculateErc8042(keccak256, 'diamond.standard.storage');

console.log(Buffer.from(slot).toString('hex'));
// "7de7edef0e40c7e2c3f605e6af81b038a7b4dd40e1f1e8c7f3f7d9e4f5c3b2a1"

Defined in: src/primitives/Storage/calculateErc8042.js

Formula

result = keccak256(id)

Simple single hash of the namespace identifier. No byte manipulation or decrementation.

Usage Patterns

Diamond Standard Storage

import { calculateErc8042 } from '@tevm/voltaire/Storage';
import { keccak256 } from '@tevm/voltaire/crypto';

// Calculate storage for diamond facets
const facetSlot = calculateErc8042(keccak256, 'diamond.storage.facet');
const ownerSlot = calculateErc8042(keccak256, 'diamond.storage.owner');

// Convert for Solidity
const hexSlot = '0x' + Buffer.from(facetSlot).toString('hex');

console.log(`
library DiamondStorage {
  bytes32 constant DIAMOND_STORAGE_POSITION = ${hexSlot};

  struct FacetStorage {
    address[] facets;
    mapping(bytes4 => address) selectorToFacet;
  }

  function diamondStorage() internal pure returns (FacetStorage storage ds) {
    bytes32 position = DIAMOND_STORAGE_POSITION;
    assembly {
      ds.slot := position
    }
  }
}
`);

Legacy Diamond Implementations

import { calculateErc8042 } from '@tevm/voltaire/Storage';
import { keccak256 } from '@tevm/voltaire/crypto';

// Common diamond storage locations
const DIAMOND_STORAGE = calculateErc8042(keccak256, 'diamond.standard.diamond.storage');
const OWNERSHIP_STORAGE = calculateErc8042(keccak256, 'diamond.standard.ownership.storage');
const ACCESS_CONTROL = calculateErc8042(keccak256, 'diamond.standard.access.control');

// These match existing diamond implementations

When to Use ERC-8042

Use ERC-8042 when:

• Implementing EIP-2535 Diamond Standard
• Compatibility with existing diamond contracts required
• Following established diamond patterns
• Simpler formula preferred

Use ERC-7201 when:

• General upgradeable proxy patterns
• Need related storage slots (last byte cleared)
• Maximum collision resistance required
• Not tied to diamond standard

Comparison with ERC-7201

Feature	ERC-8042	ERC-7201
Formula	keccak256(id)	keccak256(keccak256(id) - 1) & ~0xff
Complexity	Simple	More complex
Related slots	None	256 (last byte)
Collision resistance	Standard	Higher
Gas cost	Slightly lower	Slightly higher
Primary use	Diamond Standard	General proxies

Diamond Standard Integration

import { calculateErc8042 } from '@tevm/voltaire/Storage';
import { keccak256 } from '@tevm/voltaire/crypto';

// Generate storage slots for facets
const facets = [
  'OwnershipFacet',
  'DiamondCutFacet',
  'DiamondLoupeFacet',
  'ERC20Facet',
  'ERC721Facet'
];

const slots = facets.map(name => ({
  name,
  namespace: `diamond.${name.toLowerCase()}.storage`,
  slot: calculateErc8042(keccak256, `diamond.${name.toLowerCase()}.storage`)
}));

slots.forEach(({ name, namespace, slot }) => {
  console.log(`${name}:`);
  console.log(`  Namespace: ${namespace}`);
  console.log(`  Slot: 0x${Buffer.from(slot).toString('hex')}`);
});

See Also

• calculateErc7201 - Enhanced namespaced storage
• ERC-8042 Specification
• EIP-2535 Diamond Standard
• Keccak256 - Hash function documentation