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Add blockhash to docs (#5653)

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Co-authored-by: ernestognw <ernestognw@gmail.com>
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2025-04-29 19:04:32 -04:00
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docs/modules/ROOT/pages/utilities.adoc
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@ -386,3 +386,22 @@ await instance.multicall([
instance.interface.encodeFunctionData("bar")
]);
----
=== Historical Block Hashes
xref:api:utils.adoc#Blockhash[`Blockhash`] provides L2 protocol developers with extended access to historical block hashes beyond Ethereum's native 256-block limit. By leveraging https://eips.ethereum.org/EIPS/eip-2935[EIP-2935]'s history storage contract, the library enables access to block hashes up to 8,191 blocks in the past, making it invaluable for L2 fraud proofs and state verification systems.
The library seamlessly combines native `BLOCKHASH` opcode access for recent blocks (≤256) with EIP-2935 history storage queries for older blocks (257-8,191). It handles edge cases gracefully by returning zero for future blocks or those beyond the history window, matching the EVM's behavior. The implementation uses gas-efficient assembly for static calls to the history storage contract.
[source,solidity]
----
contract L1Inbox {
using Blockhash for uint256;
function verifyBlockHash(uint256 blockNumber, bytes32 expectedHash) public view returns (bool) {
return blockNumber.blockHash() == expectedHash;
}
}
----
IMPORTANT: After EIP-2935 activation, it takes 8,191 blocks to completely fill the history storage. Before that, only block hashes since the fork block will be available.