Encode/decode index mapping

Author: geonove

ddsketch/CMakeLists.txt

@@ -63,4 +63,5 @@ install(FILES
         include/quadratically_interpolated_mapping.hpp
         include/quadratically_interpolated_mapping_impl.hpp
         include/store.hpp
+        include/index_mapping_decode.hpp
         DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/DataSketches")

ddsketch/include/index_mapping_decode.hpp

@@ -0,0 +1,35 @@
+//
+// Created by Andrea Novellini on 13/09/2025.
+//
+
+#ifndef DATASKETCHES_INDEX_MAPPING_DECODE_HPP
+#define DATASKETCHES_INDEX_MAPPING_DECODE_HPP
+
+#include "index_mapping.hpp"
+#include "logarithmic_mapping.hpp"
+#include "quadratically_interpolated_mapping.hpp"
+
+namespace datasketches {
+
+template<class Derived>
+template<IndexMappingLayout layout>
+IndexMapping<Derived>* IndexMapping<Derived>::decode(std::istream& is) const {
+  const auto gamma = read<double>(is);
+  const auto index_offset = read<double>(is);
+
+  switch (layout) {
+    case IndexMappingLayout::LOG:
+      return new LogarithmicMapping(gamma, index_offset);
+    case IndexMappingLayout::LOG_LINEAR:
+      return new LinearlyInterpolatedMapping(gamma, index_offset);
+    case IndexMappingLayout::LOG_QUADRATIC:
+      return new QuadraticallyInterpolatedMapping(gamma, index_offset);
+    case IndexMappingLayout::LOG_QUARTIC:
+      return new QuadraticallyInterpolatedMapping(gamma, index_offset);
+    default:
+      throw std::invalid_argument("Invalid index mapping layout");
+  }
+}
+}
+
+#endif //DATASKETCHES_INDEX_MAPPING_DECODE_HPP

ddsketch/include/index_mapping_impl.hpp

@@ -22,7 +22,9 @@
 
 #include <istream>
 
+#include "common_defs.hpp"
 #include "index_mapping.hpp"
+#include "linearly_interpolated_mapping.hpp"
 
 namespace datasketches {
 
@@ -42,18 +44,6 @@ inline std::ostream& operator<<(std::ostream& os, const IndexMappingLayout& obj)
       return os << "INVALID";
   }
 }
-
-template<class Derived>
-template<IndexMappingLayout layout>
-IndexMapping<Derived>* IndexMapping<Derived>::decode(std::istream& is) {
-  switch (layout) {
-    case IndexMappingLayout::LOG_LINEAR:
-      return nullptr;
-    default:
-      return nullptr;
-  }
-}
-
 }
 
 

ddsketch/include/log_like_index_mapping.hpp

@@ -38,7 +38,7 @@ class LogLikeIndexMapping : public IndexMapping<Derived> {
   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;
 
   bool operator==(const LogLikeIndexMapping<Derived>& other) const;
 

ddsketch/include/log_like_index_mapping_impl.hpp

@@ -21,7 +21,7 @@
 #define LOG_LIKE_INDEX_MAPPING_IMPL_HPP
 #include "log_like_index_mapping.hpp"
 #include <cmath>
-#include <iomanip>
+#include "common_defs.hpp"
 
 namespace datasketches {
 
@@ -102,8 +102,10 @@ double LogLikeIndexMapping<Derived>::max_indexable_value() const {
 }
 
 template<class Derived>
-void LogLikeIndexMapping<Derived>::encode(std::ostream &os) {
-  // TODO implement
+void LogLikeIndexMapping<Derived>::serialize(std::ostream &os) const {
+  // write(os, layout());
+  write(os, gamma);
+  write(os, index_offset);
 }
 
 template<class Derived>