src/zk/gadget: added configure for less_than gadget

src/zk/gadget/less_than.rs

@@ -0,0 +1,92 @@
+use std::marker::PhantomData;
+
+use group::ff::PrimeFieldBits;
+use halo2_proofs::{
+    arithmetic::FieldExt,
+    circuit::Chip,
+    plonk::{Advice, Column, ConstraintSystem, Selector},
+    poly::Rotation,
+};
+
+use super::range_check::{RangeCheckChip, RangeCheckConfig};
+
+#[derive(Clone, Debug)]
+pub struct LessThanConfig {
+    pub s_lt: Selector,
+    pub a: Column<Advice>,
+    pub b: Column<Advice>,
+    pub a_offset: Column<Advice>,
+    pub range_a_config: RangeCheckConfig,
+    pub range_a_offset_config: RangeCheckConfig,
+}
+
+#[derive(Clone, Debug)]
+pub struct LessThanChip<
+    F: FieldExt + PrimeFieldBits,
+    const NUM_OF_BITS: usize,
+    const WINDOW_SIZE: usize,
+    const NUM_OF_WINDOWS: usize,
+> {
+    config: LessThanConfig,
+    _marker: PhantomData<F>,
+}
+
+impl<
+        F: FieldExt + PrimeFieldBits,
+        const NUM_OF_BITS: usize,
+        const WINDOW_SIZE: usize,
+        const NUM_OF_WINDOWS: usize,
+    > Chip<F> for LessThanChip<F, NUM_OF_BITS, WINDOW_SIZE, NUM_OF_WINDOWS>
+{
+    type Config = LessThanConfig;
+    type Loaded = ();
+
+    fn config(&self) -> &Self::Config {
+        &self.config
+    }
+
+    fn loaded(&self) -> &Self::Loaded {
+        &()
+    }
+}
+
+impl<
+        F: FieldExt + PrimeFieldBits,
+        const NUM_OF_BITS: usize,
+        const WINDOW_SIZE: usize,
+        const NUM_OF_WINDOWS: usize,
+    > LessThanChip<F, NUM_OF_BITS, WINDOW_SIZE, NUM_OF_WINDOWS>
+{
+    pub fn construct(config: LessThanConfig) -> Self {
+        Self { config, _marker: PhantomData }
+    }
+
+    pub fn configure(
+        meta: &mut ConstraintSystem<F>,
+        a: Column<Advice>,
+        b: Column<Advice>,
+        a_offset: Column<Advice>,
+    ) -> LessThanConfig {
+        let s_lt = meta.selector();
+
+        // configure range check for `a` and `offset`
+        let k_values_table = meta.lookup_table_column();
+        let range_a_config = RangeCheckChip::<F, WINDOW_SIZE>::configure(meta, k_values_table);
+        let range_a_offset_config =
+            RangeCheckChip::<F, WINDOW_SIZE>::configure(meta, k_values_table);
+
+        let config = LessThanConfig { s_lt, a, b, a_offset, range_a_config, range_a_offset_config };
+
+        meta.create_gate("a_offset - 2^m + b - a", |meta| {
+            let s_lt = meta.query_selector(config.s_lt);
+            let a = meta.query_advice(config.a, Rotation::cur());
+            let b = meta.query_advice(config.b, Rotation::cur());
+            let a_offset = meta.query_advice(config.a_offset, Rotation::cur());
+
+            // a_offset - 2^m + b - a = 0
+            vec![s_lt * (a_offset + b - a)]
+        });
+
+        config
+    }
+}

src/zk/gadget/mod.rs

@@ -12,3 +12,6 @@ pub mod cmp;
 
 /// Range check gadget;
 pub mod range_check;
+
+/// Less than gadget
+pub mod less_than;

src/zk/gadget/range_check.rs

@@ -1,5 +1,4 @@
 use std::marker::PhantomData;
-
 use group::ff::PrimeFieldBits;
 use halo2_proofs::{
     arithmetic::FieldExt,