Generic transaction decompressor

[Agusx1211]

This decompressor contract can handle compressed sequence transactions; everything can be compressed (nonce, address, transactions, signature). The compression methods are:

• Packing of data (remove extra 0s from ABI encoding)
• References to duplicated data
• Alternative representation of numbers (2**N, 2**N - 1, 10**N * X, etc.)
• Known values (function signatures, transaction structure, etc.)
• Cache data on contract storage (when calldata is more expensive than storage)

Current gas savings for compressed data are:

• ~15% when used on L1s
• ~50% when used on L2s

The decompressor is written in huff as it does not need to be trusted; it has no special permissions. It works as a state machine that has the only task of inflating the transactions.

It additionally can:

• Execute many compressed transactions at once
• Present the stored cache (to be used by a second version)
• Decompress a transaction without executing it

Notice that, in an attempt to reduce gas costs, the contract does not have standard Solidity selectors; it instead only uses the first single byte as a selector. The following methods do exist:

• 0x00: Decompress and execute a transaction
• 0x01: Decompress and execute many transactions
• 0x02: Read the cached address on index (takes 32 bytes as a parameter)
• 0x03: Read the cached bytes32 on index (takes 32 bytes as a parameter)
• 0x04: Returns the count of cached values (packed, uses 16 bytes for each)
• 0x05: Reads N storage slots (takes 32 x N parameters, without size prefix)
• 0x06: Decompress and return the execution data of a transaction
• 0x07: Decompress and return the execution data of many transactions

Any other selector will lead to undefined behavior. Similarly, the contract uses CALLVALUE as a replacement for PUSH0, so it MUST be called with msg.value == 0; the contract does not validate it, sending funds to it will result in undefined behavior.