Move Permutation struct from crate::circuit -> plonk::circuit

examples/simple-example.rs

@@ -4,9 +4,11 @@ use std::marker::PhantomData;
 
 use halo2::{
     arithmetic::FieldExt,
-    circuit::{layouter::SingleChip, Cell, Chip, Layouter, Permutation},
+    circuit::{layouter::SingleChip, Cell, Chip, Layouter},
     dev::VerifyFailure,
-    plonk::{Advice, Assignment, Circuit, Column, ConstraintSystem, Error, Fixed, Instance},
+    plonk::{
+        Advice, Assignment, Circuit, Column, ConstraintSystem, Error, Fixed, Instance, Permutation,
+    },
     poly::Rotation,
 };
 

src/circuit.rs

@@ -4,7 +4,7 @@ use std::{fmt, marker::PhantomData};
 
 use crate::{
     arithmetic::FieldExt,
-    plonk::{Advice, Any, Column, ConstraintSystem, Error, Fixed},
+    plonk::{Advice, Any, Column, Error, Fixed, Permutation},
 };
 
 pub mod layouter;
@@ -73,24 +73,6 @@ pub struct Cell {
     column: Column<Any>,
 }
 
-/// A permutation configured by a chip.
-#[derive(Clone, Debug)]
-pub struct Permutation {
-    index: usize,
-    mapping: Vec<Column<Any>>,
-}
-
-impl Permutation {
-    /// Configures a new permutation for the given columns.
-    pub fn new<F: FieldExt>(meta: &mut ConstraintSystem<F>, columns: &[Column<Any>]) -> Self {
-        let index = meta.permutation(columns);
-        Permutation {
-            index,
-            mapping: columns.iter().copied().collect(),
-        }
-    }
-}
-
 /// A region of the circuit in which a [`Chip`] can assign cells.
 ///
 /// Inside a region, the chip may freely use relative offsets; the [`Layouter`] will

src/circuit/layouter.rs

@@ -5,8 +5,8 @@ use std::collections::{HashMap, HashSet};
 use std::fmt;
 use std::marker::PhantomData;
 
-use super::{Cell, Chip, Layouter, Permutation, Region, RegionIndex, RegionStart};
-use crate::plonk::{Advice, Any, Assignment, Column, Error, Fixed};
+use super::{Cell, Chip, Layouter, Region, RegionIndex, RegionStart};
+use crate::plonk::{Advice, Any, Assignment, Column, Error, Fixed, Permutation};
 
 /// Helper trait for implementing a custom [`Layouter`].
 ///
@@ -321,18 +321,18 @@ impl<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> RegionLayouter<C>
         right: Cell,
     ) -> Result<(), Error> {
         let left_column = permutation
-            .mapping
+            .mapping()
             .iter()
             .position(|c| c == &left.column)
             .ok_or(Error::SynthesisError)?;
         let right_column = permutation
-            .mapping
+            .mapping()
             .iter()
             .position(|c| c == &right.column)
             .ok_or(Error::SynthesisError)?;
 
         self.layouter.cs.copy(
-            permutation.index,
+            permutation.index(),
             left_column,
             *self.layouter.regions[*left.region_index] + left.row_offset,
             right_column,

src/plonk/circuit.rs

@@ -7,6 +7,7 @@ use std::{
 };
 
 use super::{lookup, permutation, Error};
+use crate::arithmetic::FieldExt;
 use crate::poly::Rotation;
 
 /// A column type
@@ -126,6 +127,34 @@ impl TryFrom<Column<Any>> for Column<Instance> {
     }
 }
 
+/// A permutation.
+#[derive(Clone, Debug)]
+pub struct Permutation {
+    index: usize,
+    mapping: Vec<Column<Any>>,
+}
+
+impl Permutation {
+    /// Configures a new permutation for the given columns.
+    pub fn new<F: FieldExt>(meta: &mut ConstraintSystem<F>, columns: &[Column<Any>]) -> Self {
+        let index = meta.permutation(columns);
+        Permutation {
+            index,
+            mapping: columns.iter().copied().collect(),
+        }
+    }
+
+    /// Returns index of permutation
+    pub fn index(&self) -> usize {
+        self.index
+    }
+
+    /// Returns mapping of permutation
+    pub fn mapping(&self) -> &[Column<Any>] {
+        &self.mapping
+    }
+}
+
 /// This trait allows a [`Circuit`] to direct some backend to assign a witness
 /// for a constraint system.
 pub trait Assignment<F: Field> {