Adding honk composer (#18)

* Basic split and honk composer

* A single fix for gcc

* Renamed the circuit constructor

Author: Rumata888

cpp/src/aztec/honk/circuit_constructors/circuit_constructor_base.cpp

@@ -0,0 +1,43 @@
+#include "circuit_constructor_base.hpp"
+
+namespace waffle {
+
+/**
+ * Join variable class b to variable class a.
+ *
+ * @param a_variable_idx Index of a variable in class a.
+ * @param b_variable_idx Index of a variable in class b.
+ * @param msg Class tag.
+ * */
+void CircuitConstructorBase::assert_equal(const uint32_t a_variable_idx,
+                                          const uint32_t b_variable_idx,
+                                          std::string const& msg)
+{
+    assert_valid_variables({ a_variable_idx, b_variable_idx });
+    bool values_equal = (get_variable(a_variable_idx) == get_variable(b_variable_idx));
+    if (!values_equal && !failed()) {
+        failure(msg);
+    }
+    uint32_t a_real_idx = real_variable_index[a_variable_idx];
+    uint32_t b_real_idx = real_variable_index[b_variable_idx];
+    // If a==b is already enforced, exit method
+    if (a_real_idx == b_real_idx)
+        return;
+    // Otherwise update the real_idx of b-chain members to that of a
+
+    auto b_start_idx = get_first_variable_in_class(b_variable_idx);
+    update_real_variable_indices(b_start_idx, a_real_idx);
+    // Now merge equivalence classes of a and b by tying last (= real) element of b-chain to first element of a-chain
+    auto a_start_idx = get_first_variable_in_class(a_variable_idx);
+    next_var_index[b_real_idx] = a_start_idx;
+    prev_var_index[a_start_idx] = b_real_idx;
+    bool no_tag_clash = (real_variable_tags[a_real_idx] == DUMMY_TAG || real_variable_tags[b_real_idx] == DUMMY_TAG ||
+                         real_variable_tags[a_real_idx] == real_variable_tags[b_real_idx]);
+    if (!no_tag_clash && !failed()) {
+        failure(msg);
+    }
+    if (real_variable_tags[a_real_idx] == DUMMY_TAG)
+        real_variable_tags[a_real_idx] = real_variable_tags[b_real_idx];
+}
+
+} // namespace waffle