Computing Poseidon[0] hashes is too expensive to be done in a Solana
program in one transaction. Poseidon is a zero-knowlege proof friendly
hash function, used by the majority of ZK-based projects, including the
ones built on top of Solana.
This change introduces the `sol_poseidon` syscall which takes 2D byte
slice as an input and then calculates a Poseidon hash using a BN254
curve and the following Poseidon parameters:
* x^5 S-boxes
* width - 2 ≤ t ≤ 13
* inputs - 1 ≤ n ≤ 12
* 8 full rounds and partial rounds depending on t: [56, 57, 56, 60, 60,
63, 64, 63, 60, 66, 60, 65]
Computation of Poseidon hashes is done with the light-poseidon[1]
crate, which is audited[2] and compatible with Circom[3] (BN254 curve,
the same parameters and constants).
Proposed compute costs depend on number of inputs and are based on
light-poseidon benchmarks[4].
[0] https://www.poseidon-hash.info/
[1] https://crates.io/crates/light-poseidon
[2] https://github.com/Lightprotocol/light-poseidon/blob/main/assets/audit.pdf
[3] https://docs.circom.io/
[4] https://github.com/Lightprotocol/light-poseidon/tree/main#performance
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