#ifndef STAN_MATH_REV_SCAL_FUN_ROUND_HPP
#define STAN_MATH_REV_SCAL_FUN_ROUND_HPP

#include <stan/math/rev/core.hpp>
#include <stan/math/prim/scal/fun/is_nan.hpp>
#include <stan/math/prim/scal/fun/round.hpp>
#include <limits>

namespace stan {
namespace math {

namespace {
class round_vari : public op_v_vari {
 public:
  explicit round_vari(vari* avi) : op_v_vari(round(avi->val_), avi) {}
  void chain() {
    if (unlikely(is_nan(avi_->val_)))
      avi_->adj_ = std::numeric_limits<double>::quiet_NaN();
  }
};
}  // namespace

/**
 * Returns the rounded form of the specified variable (C99).
 *
 * The derivative is zero everywhere but numbers half way between
 * whole numbers, so for convenience the derivative is defined to
 * be everywhere zero,
 *
 * \f$\frac{d}{dx} \mbox{round}(x) = 0\f$.
 *
 *
   \f[
   \mbox{round}(x) =
   \begin{cases}
     \lceil x \rceil & \mbox{if } x-\lfloor x\rfloor \geq 0.5 \\
     \lfloor x \rfloor & \mbox{if } x-\lfloor x\rfloor < 0.5 \\[6pt]
     \textrm{NaN} & \mbox{if } x = \textrm{NaN}
   \end{cases}
   \f]

   \f[
   \frac{\partial\, \mbox{round}(x)}{\partial x} =
   \begin{cases}
     0 & \mbox{if } -\infty\leq x\leq \infty \\[6pt]
     \textrm{NaN} & \mbox{if } x = \textrm{NaN}
   \end{cases}
   \f]
 *
 * @param a Specified variable.
 * @return Rounded variable.
 */
inline var round(const var& a) { return var(new round_vari(a.vi_)); }

}  // namespace math
}  // namespace stan
#endif
