Fix libsnark dependency build.

This changes libsnark to build in-place, instead of copying first to
a build directory. Previously, modifications made to the original
sources wouldn't get rebuilt without a 'make clean' because users
would be pointing to the copies.

This closes #2689.

src/snark/libsnark/gadgetlib1/gadgets/gadget_from_r1cs.tcc

@@ -0,0 +1,123 @@
+/** @file
+ *****************************************************************************
+
+ Implementation of interfaces for a gadget that can be created from an R1CS constraint system.
+
+ See gadget_from_r1cs.hpp .
+
+ *****************************************************************************
+ * @author     This file is part of libsnark, developed by SCIPR Lab
+ *             and contributors (see AUTHORS).
+ * @copyright  MIT license (see LICENSE file)
+ *****************************************************************************/
+
+#ifndef GADGET_FROM_R1CS_TCC_
+#define GADGET_FROM_R1CS_TCC_
+
+namespace libsnark {
+
+template<typename FieldT>
+gadget_from_r1cs<FieldT>::gadget_from_r1cs(protoboard<FieldT> &pb,
+                                           const std::vector<pb_variable_array<FieldT> > &vars,
+                                           const r1cs_constraint_system<FieldT> &cs,
+                                           const std::string &annotation_prefix) :
+    gadget<FieldT>(pb, annotation_prefix),
+    vars(vars),
+    cs(cs)
+{
+    cs_to_vars[0] = 0; /* constant term maps to constant term */
+
+    size_t cs_var_idx = 1;
+    for (auto va : vars)
+    {
+#ifdef DEBUG
+        printf("gadget_from_r1cs: translating a block of variables with length %zu\n", va.size());
+#endif
+        for (auto v : va)
+        {
+            cs_to_vars[cs_var_idx] = v.index;
+
+#ifdef DEBUG
+            if (v.index != 0)
+            {
+                // handle annotations, except for re-annotating constant term
+                const std::map<size_t, std::string>::const_iterator it = cs.variable_annotations.find(cs_var_idx);
+
+                std::string annotation = FMT(annotation_prefix, " variable_%zu", cs_var_idx);
+                if (it != cs.variable_annotations.end())
+                {
+                    annotation = annotation_prefix + " " + it->second;
+                }
+
+                pb.augment_variable_annotation(v, annotation);
+            }
+#endif
+            ++cs_var_idx;
+        }
+    }
+
+#ifdef DEBUG
+    printf("gadget_from_r1cs: sum of all block lengths: %zu\n", cs_var_idx-1);
+    printf("gadget_from_r1cs: cs.num_variables(): %zu\n", cs.num_variables());
+#endif
+
+    assert(cs_var_idx - 1 == cs.num_variables());
+}
+
+template<typename FieldT>
+void gadget_from_r1cs<FieldT>::generate_r1cs_constraints()
+{
+    for (size_t i = 0; i < cs.num_constraints(); ++i)
+    {
+        const r1cs_constraint<FieldT> &constr = cs.constraints[i];
+        r1cs_constraint<FieldT> translated_constr;
+
+        for (const linear_term<FieldT> &t: constr.a.terms)
+        {
+            translated_constr.a.terms.emplace_back(linear_term<FieldT>(pb_variable<FieldT>(cs_to_vars[t.index]), t.coeff));
+        }
+
+        for (const linear_term<FieldT> &t: constr.b.terms)
+        {
+            translated_constr.b.terms.emplace_back(linear_term<FieldT>(pb_variable<FieldT>(cs_to_vars[t.index]), t.coeff));
+        }
+
+        for (const linear_term<FieldT> &t: constr.c.terms)
+        {
+            translated_constr.c.terms.emplace_back(linear_term<FieldT>(pb_variable<FieldT>(cs_to_vars[t.index]), t.coeff));
+        }
+
+        std::string annotation = FMT(this->annotation_prefix, " constraint_%zu", i);
+
+#ifdef DEBUG
+        auto it = cs.constraint_annotations.find(i);
+        if (it != cs.constraint_annotations.end())
+        {
+            annotation = this->annotation_prefix + " " + it->second;
+        }
+#endif
+        this->pb.add_r1cs_constraint(translated_constr, annotation);
+    }
+}
+
+template<typename FieldT>
+void gadget_from_r1cs<FieldT>::generate_r1cs_witness(const r1cs_primary_input<FieldT> &primary_input,
+                                                     const r1cs_auxiliary_input<FieldT> &auxiliary_input)
+{
+    assert(cs.num_inputs() == primary_input.size());
+    assert(cs.num_variables() == primary_input.size() + auxiliary_input.size());
+
+    for (size_t i = 0; i < primary_input.size(); ++i)
+    {
+        this->pb.val(pb_variable<FieldT>(cs_to_vars[i+1])) = primary_input[i];
+    }
+
+    for (size_t i = 0; i < auxiliary_input.size(); ++i)
+    {
+        this->pb.val(pb_variable<FieldT>(cs_to_vars[primary_input.size()+i+1])) = auxiliary_input[i];
+    }
+}
+
+} // libsnark
+
+#endif // GADGET_FROM_R1CS_TCC_