fix chrono duration rounding with leading zeroes

fmtlib · Jan 16, 2024 · 8227a2f · 8227a2f
1 parent 13ec66b
commit 8227a2f
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Showing 3 changed files with 42 additions and 7 deletions.
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -140,7 +140,7 @@ set_verbose(FMT_INC_DIR ${CMAKE_INSTALL_INCLUDEDIR} CACHE STRING
             "Installation directory for include files, a relative path that "
             "will be joined with ${CMAKE_INSTALL_PREFIX} or an absolute path.")
 
-option(FMT_PEDANTIC "Enable extra warnings and expensive tests." OFF)
+option(FMT_PEDANTIC "Enable extra warnings and expensive tests." ON)
 option(FMT_WERROR "Halt the compilation with an error on compiler warnings."
        OFF)
 

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
@@ -1154,15 +1154,38 @@ void write_fractional_seconds(OutputIt& out, Duration d, int precision = -1) {
   } else {
     *out++ = '.';
     leading_zeroes = (std::min)(leading_zeroes, precision);
-    out = std::fill_n(out, leading_zeroes, '0');
     int remaining = precision - leading_zeroes;
-    if (remaining != 0 && remaining < num_digits) {
-      n /= to_unsigned(detail::pow10(to_unsigned(num_digits - remaining)));
-      out = format_decimal<Char>(out, n, remaining).end;
+    if (remaining < num_digits) { 
+      int num_truncated_digits = num_digits - remaining;
+      n /= to_unsigned(detail::pow10(to_unsigned(num_truncated_digits)-1)); //002999
+      const int old_num_digits = detail::count_digits(n);
+      int roundingDigit = n % 10;
+      n /= 10;
+      if (roundingDigit > 5 || (roundingDigit == 5 && n % 10 % 2 != 0)) {
+        n += 1;
+      } 
+      if (old_num_digits == detail::count_digits(n)) {
+        if (leading_zeroes) {
+          out = std::fill_n(out, leading_zeroes-1, '0');
+          *out++ = '1';
+          out = std::fill_n(out, remaining, '0');
+        }
+        else {
+          n -= 1;
+          out = format_decimal<Char>(out, n, remaining).end;
+        }
+      }
+      else {
+        out = std::fill_n(out, leading_zeroes, '0');
+        out = format_decimal<Char>(out, n, remaining).end;
+      }
       return;
     }
-    out = format_decimal<Char>(out, n, num_digits).end;
-    remaining -= num_digits;
+    out = std::fill_n(out, leading_zeroes, '0');
+    if (n) {
+      out = format_decimal<Char>(out, n, num_digits).end;
+      remaining -= num_digits;
+    }
     out = std::fill_n(out, remaining, '0');
   }
 }

diff --git a/test/chrono-test.cc b/test/chrono-test.cc
@@ -791,6 +791,18 @@ TEST(chrono_test, cpp20_duration_subsecond_support) {
             "01.234000");
   EXPECT_EQ(fmt::format("{:.6%S}", std::chrono::milliseconds{-1234}),
             "-01.234000");
+  EXPECT_EQ(fmt::format("{:.2%S}", std::chrono::milliseconds{12345}),
+            "12.34");
+  EXPECT_EQ(fmt::format("{:.2%S}", std::chrono::milliseconds{12375}),
+            "12.38");
+  EXPECT_EQ(fmt::format("{:.2%S}", std::chrono::milliseconds{-12375}),
+            "-12.38");
+  EXPECT_EQ(fmt::format("{:.2%S}", std::chrono::milliseconds{12054}),
+            "12.05");
+  EXPECT_EQ(fmt::format("{:.1%S}", std::chrono::milliseconds{12054}),
+            "12.1");
+  EXPECT_EQ(fmt::format("{:.2%S}", std::chrono::milliseconds{99999}),
+            "39.99");
   EXPECT_EQ(fmt::format("{:.3%S}", std::chrono::seconds{1234}), "34.000");
   EXPECT_EQ(fmt::format("{:.3%S}", std::chrono::hours{1234}), "00.000");
   EXPECT_EQ(fmt::format("{:.5%S}", dms(1.234)), "00.00123");