text: #ifndef STAN_MATH_FWD_SCAL_FUN_EXP2_HPP
  #define STAN_MATH_FWD_SCAL_FUN_EXP2_HPP
  
  #include <stan/math/fwd/core.hpp>
  #include <stan/math/prim/scal/fun/exp2.hpp>
  #include <stan/math/prim/scal/fun/constants.hpp>
  #include <cmath>
  
  namespace stan {
    namespace math {
  
      template <typename T>
      inline fvar<T>
      exp2(const fvar<T>& x) {
        using std::log;
        return fvar<T>(exp2(x.val_), x.d_ * exp2(x.val_) * LOG_2);
      }
  
    }
  }
  #endif
  