text: #if !defined(ARCADIA_BUILD)
  #    include "config_functions.h"
  #endif
  
  #if USE_H3
  
  #include <Columns/ColumnArray.h>
  #include <Columns/ColumnsNumber.h>
  #include <DataTypes/DataTypeArray.h>
  #include <DataTypes/DataTypesNumber.h>
  #include <Functions/FunctionFactory.h>
  #include <Functions/IFunction.h>
  #include <Common/typeid_cast.h>
  #include <IO/WriteHelpers.h>
  #include <common/range.h>
  
  #include <constants.h>
  #include <h3api.h>
  
  
  static constexpr size_t MAX_ARRAY_SIZE = 1 << 30;
  
  
  namespace DB
  {
  namespace ErrorCodes
  {
      extern const int ILLEGAL_TYPE_OF_ARGUMENT;
      extern const int ARGUMENT_OUT_OF_BOUND;
      extern const int TOO_LARGE_ARRAY_SIZE;
  }
  
  namespace
  {
  
  class FunctionH3ToChildren : public IFunction
  {
  public:
      static constexpr auto name = "h3ToChildren";
  
      static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionH3ToChildren>(); }
  
      std::string getName() const override { return name; }
  
      size_t getNumberOfArguments() const override { return 2; }
      bool useDefaultImplementationForConstants() const override { return true; }
  
      DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
      {
          const auto * arg = arguments[0].get();
          if (!WhichDataType(arg).isUInt64())
              throw Exception(
                  "Illegal type " + arg->getName() + " of argument " + std::to_string(1) + " of function " + getName() + ". Must be UInt64",
                  ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
  
          arg = arguments[1].get();
          if (!WhichDataType(arg).isUInt8())
              throw Exception(
                  "Illegal type " + arg->getName() + " of argument " + std::to_string(2) + " of function " + getName() + ". Must be UInt8",
                  ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
  
          return std::make_shared<DataTypeArray>(std::make_shared<DataTypeUInt64>());
      }
  
      ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
      {
          const auto * col_hindex = arguments[0].column.get();
          const auto * col_resolution = arguments[1].column.get();
  
          auto dst = ColumnArray::create(ColumnUInt64::create());
          auto & dst_data = dst->getData();
          auto & dst_offsets = dst->getOffsets();
          dst_offsets.resize(input_rows_count);
          auto current_offset = 0;
  
          std::vector<H3Index> hindex_vec;
  
          for (const auto row : collections::range(0, input_rows_count))
          {
              const UInt64 parent_hindex = col_hindex->getUInt(row);
              const UInt8 child_resolution = col_resolution->getUInt(row);
  
              if (child_resolution > MAX_H3_RES)
                  throw Exception("The argument 'resolution' (" + toString(child_resolution) + ") of function " + getName()
                      + " is out of bounds because the maximum resolution in H3 library is " + toString(MAX_H3_RES), ErrorCodes::ARGUMENT_OUT_OF_BOUND);
  
              const size_t vec_size = maxH3ToChildrenSize(parent_hindex, child_resolution);
              if (vec_size > MAX_ARRAY_SIZE)
                  throw Exception("The result of function" + getName()
                      + " (array of " + toString(vec_size) + " elements) will be too large with resolution argument = "
                      + toString(child_resolution), ErrorCodes::TOO_LARGE_ARRAY_SIZE);
  
              hindex_vec.resize(vec_size);
              h3ToChildren(parent_hindex, child_resolution, hindex_vec.data());
  
              dst_data.reserve(dst_data.size() + vec_size);
              for (auto hindex : hindex_vec)
              {
                  if (hindex != 0)
                  {
                      ++current_offset;
                      dst_data.insert(hindex);
                  }
              }
              dst_offsets[row] = current_offset;
          }
  
          return dst;
      }
  };
  
  }
  
  void registerFunctionH3ToChildren(FunctionFactory & factory)
  {
      factory.registerFunction<FunctionH3ToChildren>();
  }
  
  }
  
  #endif
  