Resolve a compressed Arbitrum address-table index
Some Arbitrum payload formats use a short integer for a registered address. Treating the number as the low bits of an Ethereum address silently sends the decoder down the wrong path.
Resolve the index on the originating chain
When the message format explicitly marks an address-table index, query the ArbAddressTable precompile on that child chain. The example uses Foundry cast and assumes index 12 exists. If you know the address instead, lookup(address) retrieves its registered index.
cast call 0x0000000000000000000000000000000000000066 \
"lookupIndex(uint256)(address)" 12 --rpc-url "$CHILD_RPC"
Associate the resolved 20-byte address with the original table index and chain ID. An index allocated on a development chain can resolve differently on the production chain even when the payload bytes are identical.
Check the encoding variant first
A format can support both a literal address and a compressed index. Decode its discriminant before querying the table. For a historical audit, confirm that registration existed at the message’s execution context where historical state is available. docs.arbitrum.io Arbitrum documentation