added configure for RangeCheckChip

src/zk/gadget/mod.rs

@@ -9,3 +9,6 @@ pub mod even_bits;
 
 /// Comparison gadget
 pub mod cmp;
+
+/// Range check gadget;
+pub mod range_check;

src/zk/gadget/range_check.rs

@@ -0,0 +1,82 @@
+use std::marker::PhantomData;
+
+use group::ff::PrimeFieldBits;
+use halo2_proofs::{
+    arithmetic::FieldExt,
+    circuit::{Chip, Layouter, Value},
+    plonk::{Advice, Column, ConstraintSystem, Error, Selector, TableColumn},
+    poly::Rotation,
+};
+
+#[derive(Clone, Debug)]
+pub struct RangeCheckConfig {
+    pub z: Column<Advice>,
+    pub s_rc: Selector,
+    pub k_values_table: TableColumn,
+}
+
+pub struct RangeCheckChip<F: FieldExt + PrimeFieldBits, const WINDOW_SIZE: usize> {
+    config: RangeCheckConfig,
+    _marker: PhantomData<F>,
+}
+
+impl<F: FieldExt + PrimeFieldBits, const WINDOW_SIZE: usize> Chip<F>
+    for RangeCheckChip<F, WINDOW_SIZE>
+{
+    type Config = RangeCheckConfig;
+    type Loaded = ();
+
+    fn config(&self) -> &Self::Config {
+        &self.config
+    }
+
+    fn loaded(&self) -> &Self::Loaded {
+        &()
+    }
+}
+
+impl<F: FieldExt + PrimeFieldBits, const WINDOW_SIZE: usize> RangeCheckChip<F, WINDOW_SIZE> {
+    pub fn configure(
+        meta: &mut ConstraintSystem<F>,
+        k_values_table: TableColumn,
+    ) -> <Self as Chip<F>>::Config {
+        let z = meta.advice_column();
+        let s_rc = meta.complex_selector();
+
+        let config = RangeCheckConfig { z, s_rc, k_values_table };
+
+        meta.lookup(|meta| {
+            let s_rc = meta.query_selector(config.s_rc);
+            let z_curr = meta.query_advice(config.z, Rotation::cur());
+            let z_next = meta.query_advice(config.z, Rotation::next());
+
+            //    z_next = (z_curr - k_i) / 2^K
+            // => k_i = z_curr - (z_next * 2^K)
+            vec![(s_rc * (z_curr - z_next * F::from(1 << WINDOW_SIZE)), config.k_values_table)]
+        });
+
+        config
+    }
+
+    /// `k_values_table` should be reused across different chips
+    /// which is why we don't limit it to a specific instance.
+    pub fn load_k_table(
+        layouter: &mut impl Layouter<F>,
+        k_values_table: TableColumn,
+    ) -> Result<(), Error> {
+        layouter.assign_table(
+            || format!("{} window table", WINDOW_SIZE),
+            |mut table| {
+                for index in 0..(1 << WINDOW_SIZE) {
+                    table.assign_cell(
+                        || "table",
+                        k_values_table,
+                        index,
+                        || Value::known(F::from(index as u64)),
+                    )?;
+                }
+                Ok(())
+            },
+        )
+    }
+}