conditional add (doesn't work yet)

plonky2/src/gadgets/curve.rs

@@ -4,6 +4,7 @@ use plonky2_field::field_types::Field;
 use crate::curve::curve_types::{AffinePoint, Curve, CurveScalar};
 use crate::gadgets::nonnative::NonNativeTarget;
 use crate::hash::hash_types::RichField;
+use crate::iop::target::BoolTarget;
 use crate::plonk::circuit_builder::CircuitBuilder;
 
 /// A Target representing an affine point on the curve `C`. We use incomplete arithmetic for efficiency,
@@ -117,6 +118,23 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
         AffinePointTarget { x: x3, y: y3 }
     }
 
+    pub fn curve_conditional_add<C: Curve>(
+        &mut self,
+        p1: &AffinePointTarget<C>,
+        p2: &AffinePointTarget<C>,
+        b: BoolTarget,
+    ) -> AffinePointTarget<C> {
+        let to_add_x = self.mul_nonnative_by_bool(&p2.x, b);
+        let to_add_y = self.mul_nonnative_by_bool(&p2.y, b);
+        let sum_x = self.add_nonnative(&p1.x, &to_add_x);
+        let sum_y = self.add_nonnative(&p1.y, &to_add_y);
+        
+        AffinePointTarget { 
+            x: sum_x,
+            y: sum_y,
+        }
+    }
+
     pub fn curve_scalar_mul<C: Curve>(
         &mut self,
         p: &AffinePointTarget<C>,
@@ -295,6 +313,38 @@ mod tests {
         verify(proof, &data.verifier_only, &data.common)
     }
 
+    #[test]
+    fn test_curve_conditional_add() -> Result<()> {
+        const D: usize = 2;
+        type C = PoseidonGoldilocksConfig;
+        type F = <C as GenericConfig<D>>::F;
+
+        let config = CircuitConfig::standard_ecc_config();
+
+        let pw = PartialWitness::new();
+        let mut builder = CircuitBuilder::<F, D>::new(config);
+
+        let g = Secp256K1::GENERATOR_AFFINE;
+        let double_g = g.double();
+        let g_plus_2g = (g + double_g).to_affine();
+        let g_plus_2g_expected = builder.constant_affine_point(g_plus_2g);
+
+        let g_expected = builder.constant_affine_point(g);
+        let double_g_target = builder.curve_double(&g_expected);
+        let t = builder._true();
+        let f = builder._false();
+        let g_plus_2g_actual = builder.curve_conditional_add(&g_expected, &double_g_target, t);
+        let g_actual = builder.curve_conditional_add(&g_expected, &double_g_target, f);
+
+        builder.connect_affine_point(&g_plus_2g_expected, &g_plus_2g_actual);
+        builder.connect_affine_point(&g_expected, &g_actual);
+
+        let data = builder.build::<C>();
+        let proof = data.prove(pw).unwrap();
+
+        verify(proof, &data.verifier_only, &data.common)
+    }
+
     #[test]
     #[ignore]
     fn test_curve_mul() -> Result<()> {

plonky2/src/gadgets/curve_windowed_mul.rs

@@ -120,7 +120,7 @@ mod tests {
         let pw = PartialWitness::new();
         let mut builder = CircuitBuilder::<F, D>::new(config);
 
-        let num_points = 8;
+        let num_points = 16;
         let points: Vec<_> = (0..num_points)
             .map(|_| {
                 let g = (CurveScalar(Secp256K1Scalar::rand()) * Secp256K1::GENERATOR_PROJECTIVE)
@@ -130,7 +130,7 @@ mod tests {
             .collect();
 
         let mut rng = rand::thread_rng();
-        let access_index = rng.gen::<usize>() % 8;
+        let access_index = rng.gen::<usize>() % num_points;
 
         let access_index_target = builder.constant(F::from_canonical_usize(access_index));
         let selected = builder.random_access_curve_points(access_index_target, points.clone());