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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

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Formula

result = keccak256(id)
Simple single hash of the namespace identifier. No byte manipulation or decrementation.

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Usage Patterns

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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
    }
  }
}
`);

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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

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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

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Comparison with ERC-7201

FeatureERC-8042ERC-7201
Formulakeccak256(id)keccak256(keccak256(id) - 1) & ~0xff
ComplexitySimpleMore complex
Related slotsNone256 (last byte)
Collision resistanceStandardHigher
Gas costSlightly lowerSlightly higher
Primary useDiamond StandardGeneral proxies

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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')}`);
});

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See Also