From a77a5fc505bbeab1cfa36be16d40f7799689317a Mon Sep 17 00:00:00 2001
From: Paul Dreik <github@pauldreik.se>
Date: Thu, 30 May 2019 05:45:55 +0200
Subject: [PATCH] fix UB on signed int overflow in chrono_formatter constructor

see https://github.com/fmtlib/fmt/issues/1179
---
 include/fmt/chrono.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 6ec420f44bda..3f7c3f4ed1c2 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -497,8 +497,16 @@ struct chrono_formatter {
   explicit chrono_formatter(FormatContext& ctx, OutputIt o,
                             std::chrono::duration<Rep, Period> d)
       : context(ctx), out(o), val(d.count()) {
-   // hmm, what happens if this is INT_MIN?
-   if (d.count() < 0) d = -d;
+   if (d.count() < 0) {
+       //protect against signed integer overflow
+       using TT=std::numeric_limits<Rep>;
+       if(TT::is_integer && TT::is_signed) {
+           if(d.count()==TT::min()) {
+               FMT_THROW(format_error("value would cause UB"));
+           }
+       }
+       d = -d;
+   }
    
     // this may overflow and/or the result may not fit in the
     // target type.