mul_fixed::short: Refactor short::Config.

This commit does not result in circuit changes.

src/circuit/gadget/ecc/chip.rs

@@ -147,7 +147,7 @@ pub struct EccConfig {
     /// Fixed-base full-width scalar multiplication
     mul_fixed_full: mul_fixed::full_width::Config,
     /// Fixed-base signed short scalar multiplication
-    pub q_mul_fixed_short: Selector,
+    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,
 
@@ -238,6 +238,9 @@ impl EccChip {
         // 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);
 
+        // Create gate that is only used in short fixed-base scalar mul.
+        let mul_fixed_short = mul_fixed::short::Config::configure(meta, mul_fixed);
+
         let config = EccConfig {
             advices,
             add_incomplete,
@@ -245,18 +248,12 @@ impl EccChip {
             mul,
             mul_fixed,
             mul_fixed_full,
-            q_mul_fixed_short: meta.selector(),
+            mul_fixed_short,
             q_mul_fixed_base_field: meta.selector(),
             witness_point,
             lookup_config: range_check,
         };
 
-        // Create gate that is only used in short fixed-base scalar mul.
-        {
-            let short_config: mul_fixed::short::Config = (&config).into();
-            short_config.create_gate(meta);
-        }
-
         // 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();
@@ -437,7 +434,7 @@ impl EccInstructions<pallas::Affine> for EccChip {
         magnitude_sign: (CellValue<pallas::Base>, CellValue<pallas::Base>),
         base: &Self::FixedPointsShort,
     ) -> Result<(Self::Point, Self::ScalarFixedShort), Error> {
-        let config: mul_fixed::short::Config = self.config().into();
+        let config: mul_fixed::short::Config = self.config().mul_fixed_short;
         config.assign(
             layouter.namespace(|| format!("short fixed-base mul of {:?}", base)),
             magnitude_sign,

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

@@ -1,6 +1,6 @@
 use std::{array, convert::TryInto};
 
-use super::super::{EccConfig, EccPoint, EccScalarFixedShort};
+use super::super::{EccPoint, EccScalarFixedShort};
 use crate::{
     circuit::gadget::utilities::{bool_check, copy, CellValue, Var},
     constants::{ValueCommitV, L_VALUE, NUM_WINDOWS_SHORT},
@@ -13,24 +13,29 @@ use halo2::{
 };
 use pasta_curves::pallas;
 
-#[derive(Clone)]
+#[derive(Clone, Debug, Copy, Eq, PartialEq)]
 pub struct Config {
     // Selector used for fixed-base scalar mul with short signed exponent.
     q_mul_fixed_short: Selector,
     super_config: super::Config,
 }
 
-impl From<&EccConfig> for Config {
-    fn from(config: &EccConfig) -> Self {
-        Self {
-            q_mul_fixed_short: config.q_mul_fixed_short,
-            super_config: config.mul_fixed,
-        }
-    }
-}
-
 impl Config {
-    pub(crate) 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_short: meta.selector(),
+            super_config,
+        };
+
+        config.create_gate(meta);
+
+        config
+    }
+
+    fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
         meta.create_gate("Short fixed-base mul gate", |meta| {
             let q_mul_fixed_short = meta.query_selector(self.q_mul_fixed_short);
             let y_p = meta.query_advice(self.super_config.y_p, Rotation::cur());
@@ -444,7 +449,7 @@ pub mod tests {
             ) -> Result<(), Error> {
                 let column = config.advices[0];
 
-                let short_config: super::Config = (&config).into();
+                let short_config = config.mul_fixed_short;
                 let magnitude_sign = {
                     let magnitude = self.load_private(
                         layouter.namespace(|| "load magnitude"),