From 47fcd357ab6a9583f2307d1f78fdd674060efe61 Mon Sep 17 00:00:00 2001
From: khan <ajumashukurov@gmail.com>
Date: Fri, 6 Nov 2026 18:44:43 -0500
Subject: [PATCH] Avoid narrowing duration day counts to the original
 representation (#5003)

* Avoid narrowing duration day counts to the original representation

* Keep duration field values in the promoted representation

---------

Co-authored-by: Aikhan Jumashukurov <117706338+aikhanj@users.noreply.github.com>
---
 include/fmt/chrono.h | 18 +++++++-----------
 test/chrono-test.cc  | 10 ++++++++++
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index d4b44eb3..62d7a7c6 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -1703,20 +1703,16 @@ struct duration_formatter {
     return true;
   }
 
-  auto days() const -> Rep { return static_cast<Rep>(s.count() / 86400); }
-  auto hour() const -> Rep {
-    return static_cast<Rep>(mod((s.count() / 3600), 24));
-  }
+  auto days() const -> rep { return s.count() / 86400; }
+  auto hour() const -> rep { return mod((s.count() / 3600), 24); }
 
-  auto hour12() const -> Rep {
-    Rep hour = static_cast<Rep>(mod((s.count() / 3600), 12));
+  auto hour12() const -> rep {
+    auto hour = mod((s.count() / 3600), 12);
     return hour < 1 ? 12 : hour;
   }
 
-  auto minute() const -> Rep {
-    return static_cast<Rep>(mod((s.count() / 60), 60));
-  }
-  auto second() const -> Rep { return static_cast<Rep>(mod(s.count(), 60)); }
+  auto minute() const -> rep { return mod((s.count() / 60), 60); }
+  auto second() const -> rep { return mod(s.count(), 60); }
 
   auto time() const -> std::tm {
     auto time = std::tm();
@@ -1732,7 +1728,7 @@ struct duration_formatter {
     negative = false;
   }
 
-  void write(Rep value, int width, pad_type pad = pad_type::zero) {
+  void write(rep value, int width, pad_type pad = pad_type::zero) {
     write_sign();
     if (isnan(value)) return write_nan();
     uint32_or_64_or_128_t<int> n =
diff --git a/test/chrono-test.cc b/test/chrono-test.cc
index eac86bec..2b04a3a3 100644
--- a/test/chrono-test.cc
+++ b/test/chrono-test.cc
@@ -546,6 +546,16 @@ TEST(chrono_test, format_specs) {
   EXPECT_EQ(fmt::format("{:%q}", std::chrono::seconds(12345)), "s");
 }
 
+TEST(chrono_test, format_days_with_signed_char_rep) {
+  using signed_days = std::chrono::duration<signed char, std::ratio<86400>>;
+  EXPECT_EQ(fmt::format("{:%j}", signed_days(-128)), "-128");
+}
+
+TEST(chrono_test, format_days_with_unsigned_char_rep) {
+  using two_days = std::chrono::duration<unsigned char, std::ratio<172800>>;
+  EXPECT_EQ(fmt::format("{:%j}", two_days(200)), "400");
+}
+
 TEST(chrono_test, invalid_specs) {
   auto sec = std::chrono::seconds(0);
   EXPECT_THROW_MSG((void)fmt::format(runtime("{:%a}"), sec), fmt::format_error,