mul_fixed::full_width: Refactor full_width::Config.

This commit does not result in circuit changes.

src/circuit/gadget/ecc/chip.rs

@@ -145,7 +145,7 @@ pub struct EccConfig {
     pub mul_fixed: mul_fixed::Config,
 
     /// Fixed-base full-width scalar multiplication
-    pub q_mul_fixed_full: Selector,
+    mul_fixed_full: mul_fixed::full_width::Config,
     /// Fixed-base signed short scalar multiplication
     pub q_mul_fixed_short: Selector,
     /// Canonicity checks on base field element used as scalar in fixed-base mul
@@ -235,25 +235,22 @@ impl EccChip {
             add_incomplete,
         );
 
+        // Create gate that is only used in full-width fixed-base scalar mul.
+        let mul_fixed_full = mul_fixed::full_width::Config::configure(meta, mul_fixed);
+
         let config = EccConfig {
             advices,
             add_incomplete,
             add,
             mul,
             mul_fixed,
-            q_mul_fixed_full: meta.selector(),
+            mul_fixed_full,
             q_mul_fixed_short: meta.selector(),
             q_mul_fixed_base_field: meta.selector(),
             witness_point,
             lookup_config: range_check,
         };
 
-        // Create gate that is only used in full-width fixed-base scalar mul.
-        {
-            let mul_fixed_full_config: mul_fixed::full_width::Config = (&config).into();
-            mul_fixed_full_config.create_gate(meta);
-        }
-
         // Create gate that is only used in short fixed-base scalar mul.
         {
             let short_config: mul_fixed::short::Config = (&config).into();
@@ -426,7 +423,7 @@ impl EccInstructions<pallas::Affine> for EccChip {
         scalar: Option<pallas::Scalar>,
         base: &Self::FixedPoints,
     ) -> Result<(Self::Point, Self::ScalarFixed), Error> {
-        let config: mul_fixed::full_width::Config = self.config().into();
+        let config = self.config().mul_fixed_full;
         config.assign(
             layouter.namespace(|| format!("fixed-base mul of {:?}", base)),
             scalar,

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

@@ -1,4 +1,4 @@
-use super::super::{EccConfig, EccPoint, EccScalarFixed, OrchardFixedBasesFull};
+use super::super::{EccPoint, EccScalarFixed, OrchardFixedBasesFull};
 
 use crate::{
     circuit::gadget::utilities::{range_check, CellValue, Var},
@@ -12,22 +12,28 @@ use halo2::{
 };
 use pasta_curves::{arithmetic::FieldExt, pallas};
 
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct Config {
     q_mul_fixed_full: Selector,
     super_config: super::Config,
 }
 
-impl From<&EccConfig> for Config {
-    fn from(config: &EccConfig) -> Self {
-        Self {
-            q_mul_fixed_full: config.q_mul_fixed_full,
-            super_config: config.mul_fixed,
-        }
-    }
-}
-
 impl Config {
-    pub fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
+    pub(crate) fn configure(
+        meta: &mut ConstraintSystem<pallas::Base>,
+        super_config: super::Config,
+    ) -> Self {
+        let config = Self {
+            q_mul_fixed_full: meta.selector(),
+            super_config,
+        };
+
+        config.create_gate(meta);
+
+        config
+    }
+
+    fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
         // Check that each window `k` is within 3 bits
         meta.create_gate("Full-width fixed-base scalar mul", |meta| {
             let q_mul_fixed_full = meta.query_selector(self.q_mul_fixed_full);