chip::witness_point: Refactor witness_point::Config.

src/circuit/gadget/ecc/chip.rs

@@ -165,10 +165,8 @@ pub struct EccConfig {
     /// when the scalar is a signed short exponent or a base-field element.
     pub q_mul_fixed_running_sum: Selector,
 
-    /// Witness point (can be identity)
-    pub q_point: Selector,
-    /// Witness non-identity point
-    pub q_point_non_id: Selector,
+    /// Witness point
+    witness_point: witness_point::Config,
 
     /// Lookup range check using 10-bit lookup table
     pub lookup_config: LookupRangeCheckConfig<pallas::Base, { sinsemilla::K }>,
@@ -249,6 +247,9 @@ impl EccChip {
         let running_sum_config =
             RunningSumConfig::configure(meta, q_mul_fixed_running_sum, advices[4]);
 
+        // Create witness point gate
+        let witness_point = witness_point::Config::configure(meta, advices[0], advices[1]);
+
         let config = EccConfig {
             advices,
             lagrange_coeffs,
@@ -264,18 +265,11 @@ impl EccChip {
             q_mul_fixed_short: meta.selector(),
             q_mul_fixed_base_field: meta.selector(),
             q_mul_fixed_running_sum,
-            q_point: meta.selector(),
-            q_point_non_id: meta.selector(),
+            witness_point,
             lookup_config: range_check,
             running_sum_config,
         };
 
-        // Create witness point gate
-        {
-            let config: witness_point::Config = (&config).into();
-            config.create_gate(meta);
-        }
-
         // Create incomplete point addition gate
         {
             let config: add_incomplete::Config = (&config).into();
@@ -408,7 +402,7 @@ impl EccInstructions<pallas::Affine> for EccChip {
         layouter: &mut impl Layouter<pallas::Base>,
         value: Option<pallas::Affine>,
     ) -> Result<Self::Point, Error> {
-        let config: witness_point::Config = self.config().into();
+        let config = self.config().witness_point;
         layouter.assign_region(
             || "witness point",
             |mut region| config.point(value, 0, &mut region),
@@ -420,7 +414,7 @@ impl EccInstructions<pallas::Affine> for EccChip {
         layouter: &mut impl Layouter<pallas::Base>,
         value: Option<pallas::Affine>,
     ) -> Result<Self::NonIdentityPoint, Error> {
-        let config: witness_point::Config = self.config().into();
+        let config = self.config().witness_point;
         layouter.assign_region(
             || "witness non-identity point",
             |mut region| config.point_non_id(value, 0, &mut region),

src/circuit/gadget/ecc/chip/witness_point.rs

@@ -1,4 +1,4 @@
-use super::{CellValue, EccConfig, EccPoint, NonIdentityEccPoint, Var};
+use super::{CellValue, EccPoint, NonIdentityEccPoint, Var};
 
 use group::prime::PrimeCurveAffine;
 
@@ -9,7 +9,7 @@ use halo2::{
 };
 use pasta_curves::{arithmetic::CurveAffine, pallas};
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct Config {
     q_point: Selector,
     q_point_non_id: Selector,
@@ -19,19 +19,25 @@ pub struct Config {
     pub y: Column<Advice>,
 }
 
-impl From<&EccConfig> for Config {
-    fn from(ecc_config: &EccConfig) -> Self {
-        Self {
-            q_point: ecc_config.q_point,
-            q_point_non_id: ecc_config.q_point_non_id,
-            x: ecc_config.advices[0],
-            y: ecc_config.advices[1],
-        }
-    }
+impl Config {
+    pub(super) fn configure(
+        meta: &mut ConstraintSystem<pallas::Base>,
+        x: Column<Advice>,
+        y: Column<Advice>,
+    ) -> Self {
+        let config = Self {
+            q_point: meta.selector(),
+            q_point_non_id: meta.selector(),
+            x,
+            y,
+        };
+
+        config.create_gate(meta);
+
+        config
     }
 
-impl Config {
-    pub(super) fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
+    fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
         let curve_eqn = |meta: &mut VirtualCells<pallas::Base>| {
             let x = meta.query_advice(self.x, Rotation::cur());
             let y = meta.query_advice(self.y, Rotation::cur());