From 3716491ec51c34a918834857c67300eea180ba02 Mon Sep 17 00:00:00 2001
From: Paul Dreik <github@pauldreik.se>
Date: Mon, 3 Jun 2019 07:03:29 +0200
Subject: [PATCH] fix UB in on_second

---
 include/fmt/chrono.h | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 23367e58cfc3..48368408224e 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -660,7 +660,19 @@ struct chrono_formatter {
 
     if (ns == numeric_system::standard) {
       write(second(), 2);
-      auto ms = get_milliseconds(std::chrono::duration<Rep, Period>(val));
+#ifdef FMT_SAFE_DURATION_CAST
+    int ec;
+    //convert rep->Rep
+    using Crep=std::chrono::duration<rep, Period>;
+    using CRep=std::chrono::duration<Rep, Period>;
+    auto tmpval = safe_duration_cast::safe_duration_cast<CRep>(Crep{val}, ec);
+    if (ec) {
+      FMT_THROW(format_error("value would cause UB or the wrong result"));
+    }
+#else
+      auto tmpval=std::chrono::duration<Rep, Period>(val);
+#endif
+      auto ms = get_milliseconds(tmpval);
       if (ms != std::chrono::milliseconds(0)) {
         *out++ = '.';
         write(ms.count(), 3);