openvm_circuit/arch/hasher/
poseidon2.rs

1use std::{
2    array::{self, from_fn},
3    marker::PhantomData,
4};
5
6use openvm_poseidon2_air::p3_symmetric::Permutation;
7use openvm_stark_backend::p3_field::{FieldAlgebra, PrimeField32};
8use p3_baby_bear::{BabyBear, Poseidon2BabyBear};
9
10use crate::{
11    arch::{hasher::Hasher, vm_poseidon2_config, POSEIDON2_WIDTH},
12    system::memory::CHUNK,
13};
14
15pub fn vm_poseidon2_hasher<F: PrimeField32>() -> Poseidon2Hasher<F> {
16    assert_eq!(F::ORDER_U32, BabyBear::ORDER_U32, "F must be BabyBear");
17    let config = vm_poseidon2_config::<BabyBear>();
18    let (external_constants, internal_constants) =
19        config.constants.to_external_internal_constants();
20    Poseidon2Hasher {
21        poseidon2: Poseidon2BabyBear::new(external_constants, internal_constants),
22        _marker: PhantomData,
23    }
24}
25
26/// `F` must be BabyBear. Don't use this for anything performance sensitive.
27pub struct Poseidon2Hasher<F: Clone> {
28    poseidon2: Poseidon2BabyBear<POSEIDON2_WIDTH>,
29    _marker: PhantomData<F>,
30}
31
32impl<F: PrimeField32> Hasher<{ CHUNK }, F> for Poseidon2Hasher<F> {
33    fn compress(&self, lhs: &[F; CHUNK], rhs: &[F; CHUNK]) -> [F; CHUNK] {
34        let mut state = from_fn(|i| {
35            if i < CHUNK {
36                BabyBear::from_canonical_u32(lhs[i].as_canonical_u32())
37            } else {
38                BabyBear::from_canonical_u32(rhs[i - CHUNK].as_canonical_u32())
39            }
40        });
41        self.poseidon2.permute_mut(&mut state);
42        array::from_fn(|i| F::from_canonical_u32(state[i].as_canonical_u32()))
43    }
44}