How to identify the ask asset from an exchange transaction given only first 16 bytes of issuance txid

Question

In the first part of the raw exchange transaction, the metadata only contains half the issuance txid of the asset being asked for. When this raw exchange transaction is passed to decoderawexchange, multichain is able to decode the asset. My question is, how does multichain decode the asset asked for given just half the issuance txid?

Answer 1

MultiChain maintains a full list of all assets issued on the blockchain, so it's not a problem doing a lookup in this list with just the first 16 bytes of the issuance txid.

Comments

What is the rationale of using only 16 bytes for the asset lookup, Is it because the chance of a collision with another asset issuance txid beginning with the same 16 bytes is too low to become a concern?

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Precisely, it's just to save space in the transaction. The collision probability is still absolutely miniscule, if we assume that no more than a few billion assets will ever be issued on the same blockchain.