1//! This module defines traits that a step function must implement
 2use bellperson::{gadgets::num::AllocatedNum, ConstraintSystem, SynthesisError};
 3use core::marker::PhantomData;
 4use ff::PrimeField;
 5
 6/// A helper trait for a step of the incremental computation (i.e., circuit for F)
 7pub trait StepCircuit<F: PrimeField>: Send + Sync + Clone {
 8  /// Sythesize the circuit for a computation step and return variable
 9  /// that corresponds to the output of the step z_{i+1}
10  fn synthesize<CS: ConstraintSystem<F>>(
11    &self,
12    cs: &mut CS,
13    z: AllocatedNum<F>,
14  ) -> Result<AllocatedNum<F>, SynthesisError>;
15
16  /// Execute the circuit for a computation step and return output
17  fn compute(&self, z: &F) -> F;
18}
19
20/// A trivial step circuit that simply returns the input
21#[derive(Clone, Debug, Default)]
22pub struct TrivialTestCircuit<F: PrimeField> {
23  _p: PhantomData<F>,
24}
25
26impl<F> StepCircuit<F> for TrivialTestCircuit<F>
27where
28  F: PrimeField,
29{
30  fn synthesize<CS: ConstraintSystem<F>>(
31    &self,
32    _cs: &mut CS,
33    z: AllocatedNum<F>,
34  ) -> Result<AllocatedNum<F>, SynthesisError> {
35    Ok(z)
36  }
37
38  fn compute(&self, z: &F) -> F {
39    *z
40  }
41}