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Pool Config Store

To keep track of which pairs have been enabled and what parameters to use for the underlying pool the Angstrom contract maintains the Pool Config Store. To save gas on batched reads the "code as storage" aka SSTORE2 pattern is employed. Instead of using say a normal mapping to keep track of the enabled pools and their parameters the data is instead stored as a list in the form of contract bytecode.

This is because reading a single cold storage slot costs 2100 gas and holds 32 bytes while reading the code of a cold contract costs 2600 gas, but can hold up to 24576 bytes. This does come with the tradeoff that updating/adding new pools is quite expensive, which is a worthy trade off since generally >1 pair / bundle is expected & updating the config should be relatively infrequent.

Pool Config​

Every valid Angstrom pair is configured to work with 1 underlying uniswap pool. The term "pair" and "pool" may be used interchangeably in these docs.

The parameters of a pool are:

  • tick_spacing: uint16 - The tickSpacing parameter of the underlying Uniswap V4 pool
  • fee_in_e6: uint24 - The fee for limit orders in that pair in 0.000001 % (1e-6). Capped to 20%.

Pool parameters are changeable after initial configuration. The underlying Uniswap pool must be initialized separately once a new set of parameters is set.

Pool Config Store Data​

To minimize the gas cost of looking up & validating these parameters when processing an Angstrom bundle they're stored in a "store contract", this is a contract that holds the data as its raw bytecode (padded with one leading 00 byte to prevent execution/destruction).

The store's bytecode is structured as follows:

store_bytecode = safety_byte config_entry+
safety_byte = 0x00
config_entry = pool_partial_key tick_spacing fee_in_e6

Store Key​

Solidity implementation

Pools in the store are uniquely identified by their store key. The store key is derived by hashing the sorted (asset0, asset1) and then truncating the upper 5 bytes (such that every config_entry is 27 bytes).

Store Index​

The "store index" is the 0-indexed entry offset in the store e.g. if there are 5 entries total and the pool is the 3rd, its store index is 2.