Introduce BoolVar struct (#94)

* update nix and rust * introduce BoolVar, first pass * update more APIs * use true_var() and false_var() instead * update CHANGELOG * address comments
EspressoSystems · Aug 9, 2022 · 918d038 · 918d038
1 parent 682bba7
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -6,6 +6,7 @@
 - Refactored `UniversalSNARK` trait (#80, #87)
 - Restore `no_std` compliance (#85, #87)
 - Use [blst](https://github.com/supranational/blst) library for BLS signature/VRF (#89)
+- Introduce `struct BoolVar` whenever necessary and possible (#91)
 
 ## v0.1.2
 

diff --git a/nix/nixpkgs.json b/nix/nixpkgs.json
@@ -1,4 +1,4 @@
 {
-  "url": "https://github.com/nixos/nixpkgs/archive/db8ab32efd3a4ad59044848d889480954e458f25.tar.gz",
-  "sha256": "1i7ayivjm3rx62qq263jjj55m0nzhn4b99wax25kw6a8zhhwcwjb"
+  "url": "https://github.com/nixos/nixpkgs/archive/6f38b43c8c84c800f93465b2241156419fd4fd52.tar.gz",
+  "sha256": "0xw3y3jx1bcnwsc0imacbp5m8f51b66s9h8kk8qnfbckwv67dhgd"
 }
diff --git a/nix/oxalica_rust_overlay.json b/nix/oxalica_rust_overlay.json
@@ -1,7 +1,7 @@
 {
     "owner": "oxalica",
     "repo": "rust-overlay",
-    "rev": "9d7c777625640b70a4d211f62711fa316bca7176",
-    "sha256": "025bw59nl12jqf4nrvbn0a8xn03aj9bz54nvf1rb25zl2l1nkrnd",
+    "rev": "53f8467a9ef7a49c8729b28660bb83d1a75da508",
+    "sha256": "aeno3vAJm5ReC2ZCOQoZHDoNsBsqM64HgSWgqhzF6yk=",
     "fetchSubmodules": true
-}
+}
diff --git a/plonk/src/circuit/basic.rs b/plonk/src/circuit/basic.rs
@@ -5,7 +5,7 @@
 // along with the Jellyfish library. If not, see <https://mit-license.org/>.
 
 //! Basic instantiations of Plonk-based constraint systems
-use super::{Arithmetization, Circuit, GateId, Variable, WireId};
+use super::{Arithmetization, BoolVar, Circuit, GateId, Variable, WireId};
 use crate::{
     circuit::{gates::*, SortedLookupVecAndPolys},
     constants::{compute_coset_representatives, GATE_WIDTH, N_MUL_SELECTORS},
@@ -264,6 +264,18 @@ impl<F: FftField> PlonkCircuit<F> {
     pub fn range_size(&self) -> Result<usize, PlonkError> {
         Ok(1 << self.range_bit_len()?)
     }
+
+    /// creating a `BoolVar` without checking if `v` is a boolean value!
+    /// You should absolutely sure about what you are doing.
+    /// You should normally only use this API if you already enforce `v` to be a
+    /// boolean value using other constraints.
+    pub(crate) fn create_boolean_variable_unchecked(
+        &mut self,
+        a: F,
+    ) -> Result<BoolVar, PlonkError> {
+        let var = self.create_variable(a)?;
+        Ok(BoolVar::new_unchecked(var))
+    }
 }
 
 impl<F: FftField> Circuit<F> for PlonkCircuit<F> {
@@ -715,23 +727,6 @@ impl<F: FftField> PlonkCircuit<F> {
         Ok(())
     }
 
-    // Check whether the variable `var` is a boolean value
-    // this is used to return error to invalid parameter early in the circuit
-    // building development lifecycle, it should NOT be used as a circuit constraint
-    // for which you should use bool_gate() instead
-    #[inline]
-    pub(crate) fn check_bool(&self, var: Variable) -> Result<(), PlonkError> {
-        let val = self.witness(var)?;
-        if val != F::zero() && val != F::one() {
-            Err(ParameterError(
-                "Expecting a boolean value, something is wrong with your circuit logic".to_string(),
-            )
-            .into())
-        } else {
-            Ok(())
-        }
-    }
-
     // Return the variable that maps to a wire `(i, j)` where i is the wire type and
     // j is the gate index. If gate `j` is a padded dummy gate, return zero
     // variable.

diff --git a/plonk/src/circuit/customized/ecc/glv.rs b/plonk/src/circuit/customized/ecc/glv.rs
@@ -7,7 +7,7 @@
 use crate::{
     circuit::{
         customized::ecc::{MultiScalarMultiplicationCircuit, PointVariable},
-        Circuit, PlonkCircuit, Variable,
+        BoolVar, Circuit, PlonkCircuit, Variable,
     },
     errors::PlonkError,
 };
@@ -93,17 +93,10 @@ where
         self.check_var_bound(scalar)?;
         self.check_point_var_bound(base)?;
 
-        let k_vars = scalar_decomposition_gate::<_, P, _>(self, &scalar)?;
+        let (s1_var, s2_var, s2_sign_var) = scalar_decomposition_gate::<_, P, _>(self, &scalar)?;
 
         let endo_base_var = endomorphism_circuit::<_, P>(self, base)?;
-        multi_scalar_mul_circuit::<_, P>(
-            self,
-            base,
-            k_vars[0],
-            &endo_base_var,
-            k_vars[1],
-            k_vars[2],
-        )
+        multi_scalar_mul_circuit::<_, P>(self, base, s1_var, &endo_base_var, s2_var, s2_sign_var)
     }
 }
 
@@ -114,7 +107,7 @@ fn multi_scalar_mul_circuit<F, P>(
     scalar_1: Variable,
     endo_base: &PointVariable,
     scalar_2: Variable,
-    scalar_2_sign_var: Variable,
+    scalar_2_sign_var: BoolVar,
 ) -> Result<PointVariable, PlonkError>
 where
     F: PrimeField,
@@ -273,7 +266,7 @@ macro_rules! int_to_fq {
 fn scalar_decomposition_gate<F, P, S>(
     circuit: &mut PlonkCircuit<F>,
     s_var: &Variable,
-) -> Result<([Variable; 3]), PlonkError>
+) -> Result<(Variable, Variable, BoolVar), PlonkError>
 where
     F: PrimeField,
     P: TEModelParameters<BaseField = F, ScalarField = S> + Clone,
@@ -466,7 +459,7 @@ where
 
     let k1_var = circuit.create_variable(int_to_fq!(k1_int))?;
     let k2_var = circuit.create_variable(int_to_fq!(k2_int))?;
-    let k2_sign_var = circuit.create_bool_variable(is_k2_positive)?;
+    let k2_sign_var = circuit.create_boolean_variable(is_k2_positive)?;
 
     let t_var = circuit.create_variable(int_to_fq!(t_int))?;
 
@@ -521,7 +514,8 @@ where
     };
 
     //  (f.3) either f.1 or f.2 is satisfied
-    let sat = circuit.conditional_select(k2_sign_var, k2_is_neg_sat, k2_is_pos_sat)?;
+    let sat =
+        circuit.conditional_select(k2_sign_var, k2_is_neg_sat.into(), k2_is_pos_sat.into())?;
     circuit.enforce_true(sat)?;
 
     //  (g) tmp2 + lambda_2 * k2_sign * k2 + s2  = t * t_sign * r2
@@ -551,11 +545,12 @@ where
     };
 
     //  (g.3) either g.1 or g.2 is satisfied
-    let sat = circuit.conditional_select(k2_sign_var, k2_is_neg_sat, k2_is_pos_sat)?;
+    let sat =
+        circuit.conditional_select(k2_sign_var, k2_is_neg_sat.into(), k2_is_pos_sat.into())?;
     circuit.enforce_true(sat)?;
 
     // extract the output
-    Ok([k1_var, k2_var, k2_sign_var])
+    Ok((k1_var, k2_var, k2_sign_var))
 }
 
 #[cfg(test)]
@@ -702,15 +697,15 @@ mod tests {
 
             let mut circuit: PlonkCircuit<Fq> = PlonkCircuit::new_ultra_plonk(16);
             let scalar_var = circuit.create_variable(field_switching(&scalar)).unwrap();
-            let res =
+            let (k1_var, k2_var, k2_sign_var) =
                 scalar_decomposition_gate::<_, EdwardsParameters, _>(&mut circuit, &scalar_var)
                     .unwrap();
 
-            let k1_rec = circuit.witness(res[0]).unwrap();
+            let k1_rec = circuit.witness(k1_var).unwrap();
             assert_eq!(field_switching::<_, Fq>(&k1), k1_rec);
 
-            let k2_rec = circuit.witness(res[1]).unwrap();
-            let k2_sign = circuit.witness(res[2]).unwrap();
+            let k2_rec = circuit.witness(k2_var).unwrap();
+            let k2_sign = circuit.witness(k2_sign_var.into()).unwrap();
             let k2_with_sign_rec = if k2_sign == Fq::one() {
                 field_switching::<_, Fr>(&k2_rec)
             } else {