Gwc19 poly commit gadget

libsnark/gadgetlib1/gadgets/curves/scalar_multiplication.hpp

@@ -72,7 +72,8 @@ class variable_or_identity : public gadget<libff::Fr<ppT>>
     pb_variable<FieldT> is_identity_var;
 };
 
-/// Selector gadget for variable_or_identity
+/// Selector gadget for variable_or_identity. Outputs one of two
+/// variable_or_identity objects, depending on a scalar parameter.
 template<
     typename ppT,
     typename groupT,
@@ -401,6 +402,51 @@ class point_mul_by_scalar_gadget : public gadget<typename groupT::base_field>
         protoboard<Field> &pb, const std::string &annotation_prefix);
 };
 
+/// Generic gadget to perform scalar multiplication of variable_or_identity
+/// group points by scalar variables. Used by the individual group element
+/// implementations.
+template<
+    typename ppT,
+    typename groupT,
+    typename groupVarT,
+    typename selectorGadgetT,
+    typename addGadgetT,
+    typename dblGadgetT>
+class point_variable_or_identity_mul_by_scalar_gadget
+    : public gadget<typename groupT::base_field>
+{
+public:
+    using Field = libff::Fr<ppT>;
+    using nFr = libff::Fr<other_curve<ppT>>;
+
+    using varMulByScalar = point_mul_by_scalar_gadget<
+        ppT,
+        groupT,
+        groupVarT,
+        selectorGadgetT,
+        addGadgetT,
+        dblGadgetT>;
+
+    using groupVarOrIdentity = variable_or_identity<ppT, groupT, groupVarT>;
+    using selectVarIdentityGadget =
+        variable_or_identity_selector<ppT, groupT, groupVarT, selectorGadgetT>;
+
+    varMulByScalar scalar_mul;
+    groupVarOrIdentity selected_result;
+    selectVarIdentityGadget select_result;
+
+    point_variable_or_identity_mul_by_scalar_gadget(
+        protoboard<Field> &pb,
+        const pb_linear_combination<Field> &scalar,
+        const groupVarOrIdentity &P,
+        const groupVarOrIdentity &result,
+        const std::string &annotation_prefix);
+
+    void generate_r1cs_constraints();
+    void generate_r1cs_witness();
+    const groupVarOrIdentity &result() const;
+};
+
 } // namespace libsnark
 
 #include "libsnark/gadgetlib1/gadgets/curves/scalar_multiplication.tcc"

libsnark/gadgetlib1/gadgets/curves/scalar_multiplication.tcc

@@ -821,6 +821,103 @@ pb_variable_array<libff::Fr<ppT>> point_mul_by_scalar_gadget<
     return bits;
 }
 
+template<
+    typename ppT,
+    typename groupT,
+    typename groupVarT,
+    typename selectorGadgetT,
+    typename addGadgetT,
+    typename dblGadgetT>
+point_variable_or_identity_mul_by_scalar_gadget<
+    ppT,
+    groupT,
+    groupVarT,
+    selectorGadgetT,
+    addGadgetT,
+    dblGadgetT>::
+    point_variable_or_identity_mul_by_scalar_gadget(
+        protoboard<Field> &pb,
+        const pb_linear_combination<Field> &scalar,
+        const groupVarOrIdentity &P,
+        const groupVarOrIdentity &result,
+        const std::string &annotation_prefix)
+    : gadget<libff::Fr<ppT>>(pb, annotation_prefix)
+    , scalar_mul(
+          pb,
+          scalar,
+          P.value,
+          groupVarOrIdentity(pb, FMT(annotation_prefix, " scalar_mul_result")),
+          FMT(annotation_prefix, " scalar_mul"))
+    // result = P.is_identity ? P : scalar_mul_result
+    //        = select(P.is_identity, scalar_mul_result, P)
+    , selected_result(result)
+    , select_result(
+          pb,
+          P.is_identity,
+          scalar_mul.result(),
+          P,
+          selected_result,
+          FMT(annotation_prefix, " select_result"))
+{
+}
+
+template<
+    typename ppT,
+    typename groupT,
+    typename groupVarT,
+    typename selectorGadgetT,
+    typename addGadgetT,
+    typename dblGadgetT>
+void point_variable_or_identity_mul_by_scalar_gadget<
+    ppT,
+    groupT,
+    groupVarT,
+    selectorGadgetT,
+    addGadgetT,
+    dblGadgetT>::generate_r1cs_constraints()
+{
+    scalar_mul.generate_r1cs_constraints();
+    select_result.generate_r1cs_constraints();
+}
+
+template<
+    typename ppT,
+    typename groupT,
+    typename groupVarT,
+    typename selectorGadgetT,
+    typename addGadgetT,
+    typename dblGadgetT>
+void point_variable_or_identity_mul_by_scalar_gadget<
+    ppT,
+    groupT,
+    groupVarT,
+    selectorGadgetT,
+    addGadgetT,
+    dblGadgetT>::generate_r1cs_witness()
+{
+    scalar_mul.generate_r1cs_witness();
+    select_result.generate_r1cs_witness();
+}
+
+template<
+    typename ppT,
+    typename groupT,
+    typename groupVarT,
+    typename selectorGadgetT,
+    typename addGadgetT,
+    typename dblGadgetT>
+const variable_or_identity<ppT, groupT, groupVarT>
+    &point_variable_or_identity_mul_by_scalar_gadget<
+        ppT,
+        groupT,
+        groupVarT,
+        selectorGadgetT,
+        addGadgetT,
+        dblGadgetT>::result() const
+{
+    return selected_result;
+}
+
 } // namespace libsnark
 
 #endif // LIBSNARK_GADGETLIB1_GADGETS_CURVE_SCALAR_MULTIPLICATION_TCC_

libsnark/gadgetlib1/gadgets/curves/weierstrass_g1_gadget.hpp

@@ -254,6 +254,16 @@ using G1_mul_by_scalar_gadget = point_mul_by_scalar_gadget<
     G1_add_gadget<wppT>,
     G1_dbl_gadget<wppT>>;
 
+template<typename wppT>
+using G1_variable_or_identity_mul_by_scalar_gadget =
+    point_variable_or_identity_mul_by_scalar_gadget<
+        wppT,
+        libff::G1<other_curve<wppT>>,
+        G1_variable<wppT>,
+        G1_variable_selector_gadget<wppT>,
+        G1_add_gadget<wppT>,
+        G1_dbl_gadget<wppT>>;
+
 } // namespace libsnark
 
 #include <libsnark/gadgetlib1/gadgets/curves/weierstrass_g1_gadget.tcc>

libsnark/gadgetlib1/gadgets/curves/weierstrass_g2_gadget.hpp

@@ -292,6 +292,16 @@ using G2_mul_by_scalar_gadget = point_mul_by_scalar_gadget<
     G2_add_gadget<wppT>,
     G2_dbl_gadget<wppT>>;
 
+template<typename wppT>
+using G2_variable_or_identity_mul_by_scalar_gadget =
+    point_variable_or_identity_mul_by_scalar_gadget<
+        wppT,
+        libff::G2<other_curve<wppT>>,
+        G2_variable<wppT>,
+        G2_variable_selector_gadget<wppT>,
+        G2_add_gadget<wppT>,
+        G2_dbl_gadget<wppT>>;
+
 } // namespace libsnark
 
 #include <libsnark/gadgetlib1/gadgets/curves/weierstrass_g2_gadget.tcc>