distances.hpp

Go to the documentation of this file.

#ifndef KNNCOLLE_DISTANCES_HPP
#define KNNCOLLE_DISTANCES_HPP
 
#include <cmath>
 
namespace knncolle {
 
struct MockDistance {
    template<typename Output_, typename DataX_, typename DataY_, typename Dim_>
    static Output_ raw_distance(const DataX_* x, const DataY_* y, Dim_ num_dimensions) {
        Output_ output = 0;
        for (Dim_ d = 0; d < num_dimensions; ++d, ++x, ++y) {
            auto delta = static_cast<Output_>(*x) - *y; // see below for comments.
            output += delta * delta;
        }
        return output;
    }
 
    template<typename Output_>
    static Output_ normalize(Output_ raw) {
        return raw;
    }
 
    template<typename Output_>
    static Output_ denormalize(Output_ norm) {
        return norm;
    }
};
 
struct EuclideanDistance {
    template<typename Output_, typename DataX_, typename DataY_, typename Dim_>
    static Output_ raw_distance(const DataX_* x, const DataY_* y, Dim_ num_dimensions) {
        Output_ output = 0;
        for (Dim_ d = 0; d < num_dimensions; ++d, ++x, ++y) {
            auto delta = static_cast<Output_>(*x) - static_cast<Output_>(*y); // casting to ensure consistent precision regardless of DataX_, DataY_.
            output += delta * delta;
        }
        return output;
    }
 
    template<typename Output_>
    static Output_ normalize(Output_ raw) {
        return std::sqrt(raw);
    }
 
    template<typename Output_>
    static Output_ denormalize(Output_ norm) {
        return norm * norm;
    }
};
 
struct ManhattanDistance {
    template<typename Output_, typename DataX_, typename DataY_, typename Dim_>
    static Output_ raw_distance(const DataX_* x, const DataY_* y, Dim_ num_dimensions) {
        Output_ output = 0;
        for (Dim_ d = 0; d < num_dimensions; ++d, ++x, ++y) {
            output += std::abs(static_cast<Output_>(*x) - static_cast<Output_>(*y)); // casting to ensure consistent precision regardless of DataX_, DataY_.
        }
        return output;
    }
 
    template<typename Output_>
    static Output_ normalize(Output_ raw) {
        return raw;
    }
 
    template<typename Output_>
    static Output_ denormalize(Output_ norm) {
        return norm;
    }
};
 
}
 
#endif