lgamma.hpp

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#ifndef STAN_MATH_PRIM_FUN_LGAMMA_HPP
#define STAN_MATH_PRIM_FUN_LGAMMA_HPP
 
#if !__MINGW32__ && !_BOOST_LGAMMA
// _REENTRANT must be defined during compilation to ensure that cmath
// exports the reentrant safe lgamma_r version.
#if !_REENTRANT
#error \
    "stan-math requires _REENTRANT being defined during compilation" \
    "to make lgamma_r available."
#endif
#include <cmath>
#else
// MinGW compilers on Windows do not provide the reentrant lgamma_r
// such that we fall back to boost whenever we are on MinGW.
#include <stan/math/prim/fun/boost_policy.hpp>
#include <boost/math/special_functions/gamma.hpp>
#include <limits>
#endif
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/functor/apply_scalar_unary.hpp>
 
namespace stan {
namespace math {
 
inline double lgamma(double x) {
#if !__MINGW32__ && !_BOOST_LGAMMA
  int sign = 1;
  return ::lgamma_r(x, &sign);
#else
  if (unlikely(x == 0.0))
    return std::numeric_limits<double>::infinity();
  return boost::math::lgamma(x, boost_policy_t<>());
#endif
}
 
inline double lgamma(int x) {
#if !__MINGW32__ && !_BOOST_LGAMMA
  int sign = 1;
  return ::lgamma_r(x, &sign);
#else
  if (unlikely(x == 0.0))
    return std::numeric_limits<double>::infinity();
  return boost::math::lgamma(x, boost_policy_t<>());
#endif
}
 
struct lgamma_fun {
  template <typename T>
  static inline auto fun(const T& x) {
    return lgamma(x);
  }
};
 
template <typename T, require_not_var_matrix_t<T>* = nullptr,
          require_not_nonscalar_prim_or_rev_kernel_expression_t<T>* = nullptr>
inline auto lgamma(const T& x) {
  return apply_scalar_unary<lgamma_fun, T>::apply(x);
}
 
}  // namespace math
}  // namespace stan
 
#endif