Simplify duration cast

Author: vitaut

include/fmt/chrono.h

@@ -161,17 +161,6 @@ auto safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
                         int& ec) -> To {
   using From = std::chrono::duration<FromRep, FromPeriod>;
   ec = 0;
-  if (std::isnan(from.count())) {
-    // nan in, gives nan out. easy.
-    return To{std::numeric_limits<typename To::rep>::quiet_NaN()};
-  }
-  // maybe we should also check if from is denormal, and decide what to do about
-  // it.
-
-  // +-inf should be preserved.
-  if (std::isinf(from.count())) {
-    return To{from.count()};
-  }
 
   // the basic idea is that we need to convert from count() in the from type
   // to count() in the To type, by multiplying it with this:
@@ -469,6 +458,8 @@ template <typename To, typename FromRep, typename FromPeriod,
                             std::is_floating_point<typename To::rep>::value)>
 auto duration_cast(std::chrono::duration<FromRep, FromPeriod> from) -> To {
 #if FMT_SAFE_DURATION_CAST
+  // Preserve infinity and NaN.
+  if (!is_finite(from.count())) return static_cast<To>(from.count());
   // Throwing version of safe_duration_cast is only available for
   // integer to integer or float to float casts.
   int ec;