Add circuit::RegionIndex and circuit::RegionStart newtypes

src/circuit.rs

@@ -28,11 +28,47 @@ pub trait Chip: Sized {
     fn load(layouter: &mut impl Layouter<Self>) -> Result<(), Error>;
 }
 
+/// Index of a region in a layouter
+#[derive(Clone, Copy, Debug)]
+pub struct RegionIndex(usize);
+
+impl From<usize> for RegionIndex {
+    fn from(idx: usize) -> RegionIndex {
+        RegionIndex(idx)
+    }
+}
+
+impl std::ops::Deref for RegionIndex {
+    type Target = usize;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+/// Starting row of a region in a layouter
+#[derive(Clone, Copy, Debug)]
+pub struct RegionStart(usize);
+
+impl From<usize> for RegionStart {
+    fn from(idx: usize) -> RegionStart {
+        RegionStart(idx)
+    }
+}
+
+impl std::ops::Deref for RegionStart {
+    type Target = usize;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
 /// A pointer to a cell within a circuit.
 #[derive(Clone, Copy, Debug)]
 pub struct Cell {
     /// Identifies the region in which this cell resides.
-    region_index: usize,
+    region_index: RegionIndex,
     row_offset: usize,
     column: Column<Any>,
 }

src/circuit/layouter.rs

@@ -5,7 +5,7 @@ use std::collections::{HashMap, HashSet};
 use std::fmt;
 use std::marker::PhantomData;
 
-use super::{Cell, Chip, Layouter, Permutation, Region};
+use super::{Cell, Chip, Layouter, Permutation, Region, RegionIndex, RegionStart};
 use crate::plonk::{Advice, Any, Assignment, Column, Error, Fixed};
 
 /// Helper trait for implementing a custom [`Layouter`].
@@ -70,7 +70,8 @@ pub trait RegionLayouter<C: Chip>: fmt::Debug {
 pub struct SingleChip<'a, C: Chip, CS: Assignment<C::Field> + 'a> {
     cs: &'a mut CS,
     config: C::Config,
-    regions: Vec<usize>,
+    /// Stores the starting row for each region.
+    regions: Vec<RegionStart>,
     /// Stores the first empty row for each column.
     columns: HashMap<Column<Any>, usize>,
     _marker: PhantomData<C>,
@@ -115,7 +116,7 @@ impl<'a, C: Chip, CS: Assignment<C::Field> + 'a> Layouter<C> for SingleChip<'a,
         let region_index = self.regions.len();
 
         // Get shape of the region.
-        let mut shape = RegionShape::new(region_index);
+        let mut shape = RegionShape::new(region_index.into());
         {
             let region: &mut dyn RegionLayouter<C> = &mut shape;
             assignment(region.into())?;
@@ -127,7 +128,7 @@ impl<'a, C: Chip, CS: Assignment<C::Field> + 'a> Layouter<C> for SingleChip<'a,
         for column in &shape.columns {
             region_start = cmp::max(region_start, self.columns.get(column).cloned().unwrap_or(0));
         }
-        self.regions.push(region_start);
+        self.regions.push(region_start.into());
 
         // Update column usage information.
         for column in shape.columns {
@@ -135,7 +136,7 @@ impl<'a, C: Chip, CS: Assignment<C::Field> + 'a> Layouter<C> for SingleChip<'a,
         }
 
         self.cs.enter_region(name);
-        let mut region = SingleChipRegion::new(self, region_index);
+        let mut region = SingleChipRegion::new(self, region_index.into());
         let result = {
             let region: &mut dyn RegionLayouter<C> = &mut region;
             assignment(region.into())
@@ -166,14 +167,14 @@ impl<'a, C: Chip, CS: Assignment<C::Field> + 'a> Layouter<C> for SingleChip<'a,
 /// the set of columns it uses as well as the number of rows it uses.
 #[derive(Debug)]
 pub struct RegionShape {
-    region_index: usize,
+    region_index: RegionIndex,
     columns: HashSet<Column<Any>>,
     row_count: usize,
 }
 
 impl RegionShape {
     /// Create a new `RegionShape` for a region at `region_index`.
-    pub fn new(region_index: usize) -> Self {
+    pub fn new(region_index: RegionIndex) -> Self {
         RegionShape {
             region_index,
             columns: HashSet::default(),
@@ -182,7 +183,7 @@ impl RegionShape {
     }
 
     /// Get the `region_index` of a `RegionShape`.
-    pub fn region_index(&self) -> usize {
+    pub fn region_index(&self) -> RegionIndex {
         self.region_index
     }
 
@@ -245,7 +246,7 @@ impl<C: Chip> RegionLayouter<C> for RegionShape {
 
 struct SingleChipRegion<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> {
     layouter: &'r mut SingleChip<'a, C, CS>,
-    region_index: usize,
+    region_index: RegionIndex,
 }
 
 impl<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> fmt::Debug
@@ -260,7 +261,7 @@ impl<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> fmt::Debug
 }
 
 impl<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> SingleChipRegion<'r, 'a, C, CS> {
-    fn new(layouter: &'r mut SingleChip<'a, C, CS>, region_index: usize) -> Self {
+    fn new(layouter: &'r mut SingleChip<'a, C, CS>, region_index: RegionIndex) -> Self {
         SingleChipRegion {
             layouter,
             region_index,
@@ -281,7 +282,7 @@ impl<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> RegionLayouter<C>
         self.layouter.cs.assign_advice(
             annotation,
             column,
-            self.layouter.regions[self.region_index] + offset,
+            *self.layouter.regions[*self.region_index] + offset,
             to,
         )?;
 
@@ -302,7 +303,7 @@ impl<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> RegionLayouter<C>
         self.layouter.cs.assign_fixed(
             annotation,
             column,
-            self.layouter.regions[self.region_index] + offset,
+            *self.layouter.regions[*self.region_index] + offset,
             to,
         )?;
 
@@ -333,9 +334,9 @@ impl<'r, 'a, C: Chip, CS: Assignment<C::Field> + 'a> RegionLayouter<C>
         self.layouter.cs.copy(
             permutation.index,
             left_column,
-            self.layouter.regions[left.region_index] + left.row_offset,
+            *self.layouter.regions[*left.region_index] + left.row_offset,
             right_column,
-            self.layouter.regions[right.region_index] + right.row_offset,
+            *self.layouter.regions[*right.region_index] + right.row_offset,
         )?;
 
         Ok(())