Mismatch between `circuit_index` documentation and implementation (internal masks not accounted for)

[ConstanceBeguier]

Crate

ragu_pcd

Severity

low

Repo commit

4a40b3e (2nd audit leg)

Description

The documentation of circuit_index states that circuit indices are assigned in the following order: internal circuits, internal masks, internal steps, then application steps.

However, the current implementation does not account for internal masks when computing indices. Only NUM_INTERNAL_CIRCUITS and NUM_INTERNAL_STEPS are used, which makes the documented ordering inaccurate.

Code

File name: crates/ragu_pcd/src/step/mod.rs

    /// Returns the circuit index for this step.
    ///
    /// Circuits are registered in the following order: internal circuits,
    /// internal masks, internal steps, then application steps.
    ///
    /// Pass the known number of application steps to validate and compute the
    /// final index of this step. Returns an error if an application step index
    /// exceeds the number of registered steps.
    pub(crate) fn circuit_index(&self, num_application_steps: usize) -> Result<CircuitIndex> {
        match self.index {
            StepIndex::Internal(i) => {
                // Internal steps come after internal circuits
                Ok(CircuitIndex::from_u32(
                    NUM_INTERNAL_CIRCUITS as u32 + i as u32,
                ))
            }
            StepIndex::Application(i) => {
                if i >= num_application_steps {
                    return Err(ragu_core::Error::Initialization(
                            "attempted to use application Step index that exceeds Application registered steps".into(),
                        ));
                }

                Ok(CircuitIndex::new(
                    NUM_INTERNAL_STEPS + NUM_INTERNAL_CIRCUITS + i,
                ))
            }
        }
    }

Recommendations

The documentation should be updated to reflect the actual behavior.

    /// Returns the circuit index for this step.
    ///
    /// Circuits are registered in the following order: internal circuits,
    /// internal steps, then application steps.
    ///
    /// Pass the known number of application steps to validate and compute the
    /// final index of this step. Returns an error if an application step index
    /// exceeds the number of registered steps.