okapi_bm25.h

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#ifndef META_OKAPI_BM25_H_
#define META_OKAPI_BM25_H_

#include "index/ranker/ranker.h"
#include "index/ranker/ranker_factory.h"

namespace meta
{
namespace index
{

class okapi_bm25 : public ranker
{
  public:
    const static std::string id;

    const static constexpr double default_k1 = 1.2;

    const static constexpr double default_b = 0.75;

    const static constexpr double default_k3 = 500.0;

    okapi_bm25(double k1 = default_k1, double b = default_b,
               double k3 = default_k3);

    double score_one(const score_data& sd) override;

  private:
    const double k1_;
    const double b_;
    const double k3_;
};

template <>
std::unique_ptr<ranker> make_ranker<okapi_bm25>(const cpptoml::table&);
}
}
#endif