`StepCircuit` trait

Check Step Circuit first.

Also, due to the support of the halo2 ecosystem, you can learn more Circuit development from the halo2 book.

Trait

pub trait StepCircuit<const ARITY: usize, F: PrimeField> {
    type Config: Clone;

    fn configure(cs: &mut ConstraintSystem<F>) -> Self::Config;

    fn synthesize_step(
        &self,
        config: Self::Config,
        layouter: &mut impl Layouter<F>,
        z_i: &[AssignedCell<F, F>; ARITY],
    ) -> Result<[AssignedCell<F, F>; ARITY], SynthesisError>;

    fn process_step(
        &self,
        z_i: &[F; ARITY],
        k_table_size: u32,
    ) -> Result<[F; ARITY], SynthesisError>;
}

• const ARITY: usize - Each step of `IVC` structhas an input and an output (z_in, z_out), this parameter determines the size of this input.

• type Config- This type stores information about which columns and challenges we need for the circuit.

• fn configure- The function should create Config, as well as create all gates. Gadgets and chips from halo2 can be reused in this method.

• fn synthesize_step - Directly synthesize the witness, at this stage the PLONKish table must be filled in using Layouter. Gadgets and chips from halo2 can be reused in this method.

• fn process_step (optional for implementation) - This function must do the same F(z_in) -> z_out as synthesize_step. Due to some restrictions, we must supply as one of the public inputs (instance column) inside the folding scheme a hash that depends on z_out. By default, this method is done through the synthesize_step call, however, if the synthesis is long, it is possible to optimize it through a manual implementation in the off-circuit mode.