From c1d430e61ab306e0e1d454fea6e07b4f66667a65 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <victor.zverovich@gmail.com>
Date: Sat, 4 May 2019 16:33:17 -0700
Subject: [PATCH] Improve handling of negative durations

---
 include/fmt/chrono.h | 13 ++++++++-----
 test/chrono-test.cc  |  4 ++++
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 9de56df9..39369add 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -430,11 +430,14 @@ struct chrono_formatter {
 
   explicit chrono_formatter(FormatContext& ctx, OutputIt o,
                             std::chrono::duration<Rep, Period> d)
-      : context(ctx),
-        out(o),
-        val(d.count()),
-        s(std::chrono::duration_cast<seconds>(d)),
-        ms(std::chrono::duration_cast<milliseconds>(d - s)) {}
+      : context(ctx), out(o), val(d.count()) {
+    if (d.count() < 0) {
+      d = -d;
+      *out++ = '-';
+    }
+    s = std::chrono::duration_cast<seconds>(d);
+    ms = std::chrono::duration_cast<milliseconds>(d - s);
+  }
 
   int hour() const { return to_int(mod((s.count() / 3600), 24)); }
 
diff --git a/test/chrono-test.cc b/test/chrono-test.cc
index 8965af92..573606d8 100644
--- a/test/chrono-test.cc
+++ b/test/chrono-test.cc
@@ -310,4 +310,8 @@ TEST(ChronoTest, LargeDuration) {
   EXPECT_EQ("40", fmt::format("{:%S}", std::chrono::duration<double>(1e20)));
 }
 
+TEST(ChronoTest, NegativeDuration) {
+  EXPECT_EQ("-00:01", fmt::format("{:%M:%S}", std::chrono::duration<double>(-1)));
+}
+
 #endif  // FMT_STATIC_THOUSANDS_SEPARATOR