I have some mathematical algorithm I have reason to run as an on-chain function in a smart contract. After unrolling for-loops I’m looking at I’m guessing 10000 lines of code where each line is doing simple arithmetic (adding or multiplying floating point numbers in small arrays).
I know for a fact the function can be computed 3000-5000 times per second on a 2.3 GHz Intel i5, when written in C depending on parameter tweaks.
Before writing the code my ‘gut feel’ is I’m looking at 1,000,000 gas for something like this, based on some simple hardhat tests with large for-loops.
Running this on a main chain looks like a joke, but running this on Polygon or some kind of roll-up looks like it might not be ridiculously expensive?
I estimate users will need to call the function/transaction maybe 5 or 10 times total. I also estimate that the on-chain data will be around 5 kilobytes per transaction (or 2kb with on-chain decompression). The majority of participants to the smart contract would likely be willing to spend $120 total on those 5 or 10 transactions but $10000 might not be out of the question for certain corporate use-cases.
Ballpark, does this sound like it adds up or have I vastly underestimated the cost of gas or on-chain data?
Do you actually need the math function on-chain? What makes this function so special and complicated that it can’t be simplified with existing gas-efficient libraries? Have you already written up the algo in solidity? (assuming you have since you mentioned hardhat)
Have you considered using an optimistic prover? You can publish a pairing of {inputs,outputs} without actually running the algorithm, and if anyone challenges it, then they can pay the gas to run this complex algorithm (I think this can be done with ZK provers as well) and show the results were wrong. This might require some stake (0.1 ETH?) when people push new {input,output} sets though, since there needs to be a penalty for lying. Of course whoever calls you out for lying should get their gas reimbursed, plus maybe some reward.
To answer your original question, polygon or a rollup may be the right choice. Consider also: Gnosis chain and Celo. Those are fairly cheap at the moment, but still large enough to offer good security. My recent calculations were showing less than 0.03 USD per 1 million gas for all of these chains. Fuse is a very inexpensive EVM chain but is less secure due to low marketcap of the FUSE token, so keep this in mind if you expect your project to have significant TVL.
Finally, note that gas costs are primarily driven by storage reads/writes, which is non-volatile memory. “memory” in the solidity sense is expensive-ish, and that is data that doesn’t persist after the transaction finishes. Try to minimize writes/reads of storage first, then memory if possible to reduce your gas costs. Keep in mind one “read/write” is 32 bytes, so you can pack data cleverly to reduce total reads/writes