Index mapping encoding and decoding

Author: geonove

ddsketch/include/index_mapping.hpp

@@ -43,12 +43,15 @@ class IndexMapping {
   double get_relative_accuracy() const;
   double min_indexable_value() const;
   double max_indexable_value() const;
-  void encode(std::ostream& os);
+  void serialize(std::ostream& os) const;
 
-  template<IndexMappingLayout layout>
-  static IndexMapping* decode(std::istream& is);
+  static Derived deserialize(std::istream& is);
 
   ~IndexMapping() = default;
+
+protected:
+  Derived& derived();
+  const Derived& derived() const;
 };
 
 }

ddsketch/include/index_mapping_decode.hpp

@@ -24,7 +24,6 @@
 
 #include "common_defs.hpp"
 #include "index_mapping.hpp"
-#include "linearly_interpolated_mapping.hpp"
 
 namespace datasketches {
 
@@ -44,6 +43,35 @@ inline std::ostream& operator<<(std::ostream& os, const IndexMappingLayout& obj)
       return os << "INVALID";
   }
 }
+
+template<class Derived>
+Derived IndexMapping<Derived>::deserialize(std::istream &is) {
+  const auto gamma = read<double>(is);
+  const auto index_offset = read<double>(is);
+
+
+  return Derived(gamma, index_offset);
+}
+
+template<class Derived>
+Derived& IndexMapping<Derived>::derived() {
+  return *static_cast<Derived*>(this);
+}
+
+template<class Derived>
+const Derived& IndexMapping<Derived>::derived() const {
+  return *static_cast<const Derived*>(this);
+}
+
+template<class Derived>
+void IndexMapping<Derived>::serialize(std::ostream &os) const {
+  derived().serialize(os);
+}
+
+template<class Derived>
+double IndexMapping<Derived>::get_relative_accuracy() const {
+  return derived().get_relative_accuracy();
+}
 }
 
 

ddsketch/include/index_mapping_impl.hpp

@@ -102,8 +102,7 @@ double LogLikeIndexMapping<Derived>::max_indexable_value() const {
 }
 
 template<class Derived>
-void LogLikeIndexMapping<Derived>::serialize(std::ostream &os) const {
-  // write(os, layout());
+void LogLikeIndexMapping<Derived>::serialize(std::ostream& os) const {
   write(os, gamma);
   write(os, index_offset);
 }

ddsketch/include/log_like_index_mapping_impl.hpp

@@ -94,4 +94,22 @@ TEMPLATE_TEST_CASE("test index mapping validity", "[indexmappingtest}",
     bound = mapping->upper_bound(index);
   }
 }
+
+TEMPLATE_TEST_CASE("encode - decode", "[indexmappingtest",
+  LinearlyInterpolatedMapping,
+  LogarithmicMapping,
+  QuadraticallyInterpolatedMapping,
+  QuarticallyInterpolatedMapping
+) {
+  const double gamma = 42;
+  const double index_offset = 4321;
+  TestType mapping(gamma, index_offset);
+
+  std::stringstream ss;
+  mapping.serialize(ss);
+
+  const TestType decoded_mapping = IndexMapping<TestType>::deserialize(ss);
+
+  REQUIRE(mapping.get_relative_accuracy() == decoded_mapping.get_relative_accuracy());
+}
 }