Circuit: optimized short range check on 4 and 5 bits (#86)

Short range checks on 4 and 5 bits are now performed with only one
lookup (instead of 2).

With this optimization, we  could come back to k=11 in the circuit.

src/circuit.rs

@@ -68,7 +68,7 @@ mod note_commit;
 mod value_commit_orchard;
 
 /// Size of the Orchard circuit.
-const K: u32 = 12;
+const K: u32 = 11;
 
 // Absolute offsets for public inputs.
 const ANCHOR: usize = 0;
@@ -342,10 +342,12 @@ impl plonk::Circuit<pallas::Base> for Circuit {
 
         // Fixed columns for the Sinsemilla generator lookup table
         let table_idx = meta.lookup_table_column();
+        let table_range_check_tag = meta.lookup_table_column();
         let lookup = (
             table_idx,
             meta.lookup_table_column(),
             meta.lookup_table_column(),
+            table_range_check_tag,
         );
 
         // Instance column used for public inputs
@@ -381,7 +383,8 @@ impl plonk::Circuit<pallas::Base> for Circuit {
 
         // We have a lot of free space in the right-most advice columns; use one of them
         // for all of our range checks.
-        let range_check = LookupRangeCheckConfig::configure(meta, advices[9], table_idx);
+        let range_check =
+            LookupRangeCheckConfig::configure(meta, advices[9], table_idx, table_range_check_tag);
 
         // Configuration for curve point operations.
         // This uses 10 advice columns and spans the whole circuit.
@@ -1287,8 +1290,8 @@ mod tests {
                     K,
                     &circuits[0],
                 );
-            assert_eq!(usize::from(circuit_cost.proof_size(1)), 5088);
-            assert_eq!(usize::from(circuit_cost.proof_size(2)), 7360);
+            assert_eq!(usize::from(circuit_cost.proof_size(1)), 5120);
+            assert_eq!(usize::from(circuit_cost.proof_size(2)), 7392);
             usize::from(circuit_cost.proof_size(instances.len()))
         };
 
@@ -1405,7 +1408,7 @@ mod tests {
             let test_case_bytes = fs::read("src/circuit_proof_test_case.bin").unwrap();
             read_test_case(&test_case_bytes[..]).expect("proof must be valid")
         };
-        assert_eq!(proof.0.len(), 5088);
+        assert_eq!(proof.0.len(), 5120);
 
         assert!(proof.verify(&vk, &[instance]).is_ok());
     }

src/circuit/commit_ivk.rs

@@ -734,10 +734,12 @@ mod tests {
                 }
 
                 let table_idx = meta.lookup_table_column();
+                let table_range_check_tag = meta.lookup_table_column();
                 let lookup = (
                     table_idx,
                     meta.lookup_table_column(),
                     meta.lookup_table_column(),
+                    table_range_check_tag,
                 );
                 let lagrange_coeffs = [
                     meta.fixed_column(),
@@ -750,7 +752,12 @@ mod tests {
                     meta.fixed_column(),
                 ];
 
-                let range_check = LookupRangeCheckConfig::configure(meta, advices[9], table_idx);
+                let range_check = LookupRangeCheckConfig::configure(
+                    meta,
+                    advices[9],
+                    table_idx,
+                    table_range_check_tag,
+                );
                 let sinsemilla_config = SinsemillaChip::<
                     OrchardHashDomains,
                     OrchardCommitDomains,

src/circuit/gadget/mux_chip.rs

@@ -215,6 +215,7 @@ mod tests {
                     MuxChip::configure(meta, advices[0], advices[1], advices[2], advices[3]);
 
                 let table_idx = meta.lookup_table_column();
+                let table_range_check_tag = meta.lookup_table_column();
 
                 let lagrange_coeffs = [
                     meta.fixed_column(),
@@ -228,7 +229,12 @@ mod tests {
                 ];
                 meta.enable_constant(lagrange_coeffs[0]);
 
-                let range_check = LookupRangeCheckConfig::configure(meta, advices[9], table_idx);
+                let range_check = LookupRangeCheckConfig::configure(
+                    meta,
+                    advices[9],
+                    table_idx,
+                    table_range_check_tag,
+                );
 
                 let ecc_config = EccChip::<OrchardFixedBases>::configure(
                     meta,

src/circuit/note_commit.rs

@@ -2369,10 +2369,12 @@ mod tests {
                 }
 
                 let table_idx = meta.lookup_table_column();
+                let table_range_check_tag = meta.lookup_table_column();
                 let lookup = (
                     table_idx,
                     meta.lookup_table_column(),
                     meta.lookup_table_column(),
+                    table_range_check_tag,
                 );
                 let lagrange_coeffs = [
                     meta.fixed_column(),
@@ -2385,7 +2387,12 @@ mod tests {
                     meta.fixed_column(),
                 ];
 
-                let range_check = LookupRangeCheckConfig::configure(meta, advices[9], table_idx);
+                let range_check = LookupRangeCheckConfig::configure(
+                    meta,
+                    advices[9],
+                    table_idx,
+                    table_range_check_tag,
+                );
                 let sinsemilla_config = SinsemillaChip::<
                     OrchardHashDomains,
                     OrchardCommitDomains,

src/circuit/value_commit_orchard.rs

@@ -169,10 +169,12 @@ mod tests {
                 meta.enable_equality(primary);
 
                 let table_idx = meta.lookup_table_column();
+                let table_range_check_tag = meta.lookup_table_column();
                 let lookup = (
                     table_idx,
                     meta.lookup_table_column(),
                     meta.lookup_table_column(),
+                    table_range_check_tag,
                 );
 
                 let lagrange_coeffs = [
@@ -187,7 +189,12 @@ mod tests {
                 ];
                 meta.enable_constant(lagrange_coeffs[0]);
 
-                let range_check = LookupRangeCheckConfig::configure(meta, advices[9], table_idx);
+                let range_check = LookupRangeCheckConfig::configure(
+                    meta,
+                    advices[9],
+                    table_idx,
+                    table_range_check_tag,
+                );
 
                 let sinsemilla_config = SinsemillaChip::configure(
                     meta,