New cpp folder structure

Signed-off-by: Alexander Borsuk <me@alex.bio>

libs/indexer/feature_impl.cpp

@@ -0,0 +1,19 @@
+#include "indexer/feature_impl.hpp"
+
+#include <algorithm>
+#include <cmath>
+
+namespace feature
+{
+
+uint8_t PopulationToRank(uint64_t p)
+{
+  return std::min(0xFFl, std::lround(std::log(double(p)) / std::log(1.1)));
+}
+
+uint64_t RankToPopulation(uint8_t r)
+{
+  return static_cast<uint64_t>(std::pow(1.1, r));
+}
+
+} // namespace feature