binomial_coefficient_log.hpp

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#ifndef STAN_MATH_OPENCL_KERNELS_DEVICE_FUNCTIONS_BINOMIAL_COEFFICIENT_LOG_HPP
#define STAN_MATH_OPENCL_KERNELS_DEVICE_FUNCTIONS_BINOMIAL_COEFFICIENT_LOG_HPP
#ifdef STAN_OPENCL
 
#include <stan/math/opencl/stringify.hpp>
#include <string>
 
namespace stan {
namespace math {
namespace opencl_kernels {
 
// \cond
static constexpr const char* binomial_coefficient_log_device_function
    = "\n"
      "#ifndef "
      "STAN_MATH_OPENCL_KERNELS_DEVICE_FUNCTIONS_BINOMIAL_COEFFICIENT_LOG\n"
      "#define "
      "STAN_MATH_OPENCL_KERNELS_DEVICE_FUNCTIONS_BINOMIAL_COEFFICIENT_"
      "LOG\n" STRINGIFY(
          // \endcond
          double binomial_coefficient_log(double n, double k) {
            if (isnan(n) || isnan(k)) {
              return NAN;
            }
 
            // Choosing the more stable of the symmetric branches
            if (n > -1 && k > n / 2.0 + 1e-8) {
              k = n - k;
            }
 
            double n_plus_1 = n + 1;
            double n_plus_1_mk = n_plus_1 - k;
 
            if (k == 0) {
              return 0;
            } else if (n_plus_1 < LGAMMA_STIRLING_DIFF_USEFUL) {
              return lgamma(n_plus_1) - lgamma(k + 1) - lgamma(n_plus_1_mk);
            } else {
              return -lbeta(n_plus_1_mk, k + 1) - log1p(n);
            }
          }
          // \cond
          ) "\n#endif\n";  // NOLINT
// \endcond
 
}  // namespace opencl_kernels
}  // namespace math
}  // namespace stan
 
#endif
#endif  // BINOMIAL_COEFFICIENT_LOG_HPP