mul_fixed::base_field_elem: Refactor base_field_elem::Config.

This commit does not result in circuit changes.

src/circuit/gadget/ecc/chip.rs

@@ -11,10 +11,12 @@ use arrayvec::ArrayVec;
 use group::prime::PrimeCurveAffine;
 use halo2::{
     circuit::{Chip, Layouter},
-    plonk::{Advice, Column, ConstraintSystem, Error, Fixed, Selector},
+    plonk::{Advice, Column, ConstraintSystem, Error, Fixed},
 };
 use pasta_curves::{arithmetic::CurveAffine, pallas};
 
+use std::convert::TryInto;
+
 pub(super) mod add;
 pub(super) mod add_incomplete;
 pub(super) mod mul;
@@ -148,8 +150,8 @@ pub struct EccConfig {
     mul_fixed_full: mul_fixed::full_width::Config,
     /// Fixed-base signed short scalar multiplication
     mul_fixed_short: mul_fixed::short::Config,
-    /// Canonicity checks on base field element used as scalar in fixed-base mul
-    pub q_mul_fixed_base_field: Selector,
+    /// Fixed-base mul using a base field element as a scalar
+    mul_fixed_base_field: mul_fixed::base_field_elem::Config,
 
     /// Witness point
     witness_point: witness_point::Config,
@@ -196,11 +198,6 @@ impl EccChip {
         lagrange_coeffs: [Column<Fixed>; 8],
         range_check: LookupRangeCheckConfig<pallas::Base, { sinsemilla::K }>,
     ) -> <Self as Chip<pallas::Base>>::Config {
-        // The following columns need to be equality-enabled for their use in sub-configs:
-        //
-        // mul_fixed::base_field_element::Config:
-        // - [advices[6], advices[7], advices[8]]: canon_advices
-        //
         // TODO: Refactor away from `impl From<EccConfig> for _` so that sub-configs can
         // equality-enable the columns they need to.
         for column in &advices {
@@ -241,6 +238,14 @@ impl EccChip {
         // Create gate that is only used in short fixed-base scalar mul.
         let mul_fixed_short = mul_fixed::short::Config::configure(meta, mul_fixed);
 
+        // Create gate that is only used in fixed-base mul using a base field element.
+        let mul_fixed_base_field = mul_fixed::base_field_elem::Config::configure(
+            meta,
+            advices[6..9].try_into().unwrap(),
+            range_check,
+            mul_fixed,
+        );
+
         let config = EccConfig {
             advices,
             add_incomplete,
@@ -249,17 +254,11 @@ impl EccChip {
             mul_fixed,
             mul_fixed_full,
             mul_fixed_short,
-            q_mul_fixed_base_field: meta.selector(),
+            mul_fixed_base_field,
             witness_point,
             lookup_config: range_check,
         };
 
-        // Create gate that is only used in fixed-base mul using a base field element.
-        {
-            let base_field_config: mul_fixed::base_field_elem::Config = (&config).into();
-            base_field_config.create_gate(meta);
-        }
-
         config
     }
 }
@@ -448,7 +447,7 @@ impl EccInstructions<pallas::Affine> for EccChip {
         base_field_elem: CellValue<pallas::Base>,
         base: &Self::FixedPointsBaseField,
     ) -> Result<Self::Point, Error> {
-        let config: mul_fixed::base_field_elem::Config = self.config().into();
+        let config = self.config().mul_fixed_base_field;
         config.assign(
             layouter.namespace(|| format!("base-field elem fixed-base mul of {:?}", base)),
             base_field_elem,

src/circuit/gadget/ecc/chip/mul_fixed/base_field_elem.rs

@@ -1,4 +1,4 @@
-use super::super::{EccBaseFieldElemFixed, EccConfig, EccPoint, NullifierK};
+use super::super::{EccBaseFieldElemFixed, EccPoint, NullifierK};
 use super::H_BASE;
 
 use crate::{
@@ -18,6 +18,7 @@ use pasta_curves::{arithmetic::FieldExt, pallas};
 
 use std::convert::TryInto;
 
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct Config {
     q_mul_fixed_base_field: Selector,
     canon_advices: [Column<Advice>; 3],
@@ -25,13 +26,22 @@ pub struct Config {
     super_config: super::Config,
 }
 
-impl From<&EccConfig> for Config {
-    fn from(config: &EccConfig) -> Self {
+impl Config {
+    pub(crate) fn configure(
+        meta: &mut ConstraintSystem<pallas::Base>,
+        canon_advices: [Column<Advice>; 3],
+        lookup_config: LookupRangeCheckConfig<pallas::Base, { sinsemilla::K }>,
+        super_config: super::Config,
+    ) -> Self {
+        for advice in canon_advices.iter() {
+            meta.enable_equality((*advice).into());
+        }
+
         let config = Self {
-            q_mul_fixed_base_field: config.q_mul_fixed_base_field,
-            canon_advices: [config.advices[6], config.advices[7], config.advices[8]],
-            lookup_config: config.lookup_config,
-            super_config: config.mul_fixed,
+            q_mul_fixed_base_field: meta.selector(),
+            canon_advices,
+            lookup_config,
+            super_config,
         };
 
         let add_incomplete_advices = config.super_config.add_incomplete_config.advice_columns();
@@ -42,12 +52,12 @@ impl From<&EccConfig> for Config {
             );
         }
 
+        config.create_gate(meta);
+
         config
     }
-}
 
-impl Config {
-    pub fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
+    fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
         // Check that the base field element is canonical.
         meta.create_gate("Canonicity checks", |meta| {
             let q_mul_fixed_base_field = meta.query_selector(self.q_mul_fixed_base_field);