# dlib C++ Library - utilities.h

    // Copyright (C) 2016  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_DNn_UTILITIES_H_
    #define DLIB_DNn_UTILITIES_H_

    #include "../cuda/tensor.h"
    #include "utilities_abstract.h"
    #include "../geometry.h"
    #include <fstream>

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        inline void randomize_parameters (
            tensor& params,
            unsigned long num_inputs_and_outputs,
            dlib::rand& rnd
        )
        {
            for (auto& val : params)
            {
                // Draw a random number to initialize the layer according to formula (16)
                // from Understanding the difficulty of training deep feedforward neural
                // networks by Xavier Glorot and Yoshua Bengio.
                val = 2*rnd.get_random_float()-1;
                val *= std::sqrt(6.0/(num_inputs_and_outputs));
            }
        }

    // ----------------------------------------------------------------------------------------

        template <typename label_type>
        struct weighted_label
        {
            weighted_label()
            {}

            weighted_label(label_type label, float weight = 1.f)
                : label(label), weight(weight)
            {}

            label_type label{};
            float weight = 1.f;
        };

    // ----------------------------------------------------------------------------------------

        inline double log1pexp(double x)
        {
            using std::exp;
            using namespace std; // Do this instead of using std::log1p because some compilers
                                 // error out otherwise (E.g. gcc 4.9 in cygwin)
            if (x <= -37)
                return exp(x);
            else if (-37 < x && x <= 18)
                return log1p(exp(x));
            else if (18 < x && x <= 33.3)
                return x + exp(-x);
            else
                return x;
        }

    // ----------------------------------------------------------------------------------------

        template <typename T>
        T safe_log(T input, T epsilon = 1e-10)
        {
            // Prevent trying to calculate the logarithm of a very small number (let alone zero)
            return std::log(std::max(input, epsilon));
        }

    // ----------------------------------------------------------------------------------------

        static size_t tensor_index(
            const tensor& t,
            const long sample,
            const long k,
            const long r,
            const long c
        )
        {
            return ((sample * t.k() + k) * t.nr() + r) * t.nc() + c;
        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_DNn_UTILITIES_H_