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Implement c++20 std::chrono::duration subsecond formatting (#2623)
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* Add support for subsecond printing for std::chrono::duration according to the c++20 standard

* Remove assert test that overflows intmax_t

* * Hopefully fix int64_t to int32_t conversion errors.
* Allow proper Duration::rep type to propagate via template argument deduction

* * Hopefully fix int64_t to int32_t conversion errors.
* Allow proper Duration::rep type to propagate via template argument deduction

* Fix sign conversion (-Wsign-conversion) warning treated as error in num_digits()

* Format chrono.h with clang-format

* Remove extra forward slash in doxygen style comment

Co-authored-by: Victor Zverovich <[email protected]>

* Apply all suggestions from GitHub, except for replacing the utility subsecond_helper class with a function

* * Move logic of handling subseconds from utility class to function with name write_fractional_seconds()
* Revert write(Rep value, int width) function to previous state

* Fix -Wshadow warning

* Remove unsued get_subseconds() function, its logic has been moved to write_fractional_seconds()

* Change comment from lowercase int to uppercase Int

* Simplify test check

* Integrate suggested changes

* Remove static from detail functions, they are no longer member functions of a class and static is unnecessary.
* Change comment from "amount" to "number"

Co-authored-by: Victor Zverovich <[email protected]>
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@matrackif @vitaut
matrackif and vitaut authored Dec 9, 2021
1 parent 9d5b9de commit 0bbc970
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Showing 2 changed files with 111 additions and 34 deletions.
98 changes: 69 additions & 29 deletions include/fmt/chrono.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1388,21 +1388,21 @@ inline bool isfinite(T) {
return true;
}

// Converts value to int and checks that it's in the range [0, upper).
template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
inline int to_nonnegative_int(T value, int upper) {
// Converts value to Int and checks that it's in the range [0, upper).
template <typename T, typename Int, FMT_ENABLE_IF(std::is_integral<T>::value)>
inline Int to_nonnegative_int(T value, Int upper) {
FMT_ASSERT(value >= 0 && to_unsigned(value) <= to_unsigned(upper),
"invalid value");
(void)upper;
return static_cast<int>(value);
return static_cast<Int>(value);
}
template <typename T, FMT_ENABLE_IF(!std::is_integral<T>::value)>
inline int to_nonnegative_int(T value, int upper) {
template <typename T, typename Int, FMT_ENABLE_IF(!std::is_integral<T>::value)>
inline Int to_nonnegative_int(T value, Int upper) {
FMT_ASSERT(
std::isnan(value) || (value >= 0 && value <= static_cast<T>(upper)),
"invalid value");
(void)upper;
return static_cast<int>(value);
return static_cast<Int>(value);
}

template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
Expand Down Expand Up @@ -1459,15 +1459,35 @@ inline std::chrono::duration<Rep, std::milli> get_milliseconds(
#endif
}

template <typename Rep, typename Period,
FMT_ENABLE_IF(std::is_floating_point<Rep>::value)>
inline std::chrono::duration<Rep, std::milli> get_milliseconds(
// Returns the number of digits according to the c++ 20 spec
// In the range [0, 18], if more than 18 fractional digits are required,
// then we return 6 for microseconds precision.
constexpr int num_digits(long long num, long long den, int n = 0) {
return num % den == 0 ? n : (n > 18 ? 6 : num_digits(num * 10, den, n + 1));
}

constexpr long long pow10(std::uint32_t n) {
return n == 0 ? 1 : 10 * pow10(n - 1);
}

template <class Rep, class Period,
FMT_ENABLE_IF(std::numeric_limits<Rep>::is_signed)>
constexpr std::chrono::duration<Rep, Period> abs(
std::chrono::duration<Rep, Period> d) {
using common_type = typename std::common_type<Rep, std::intmax_t>::type;
auto ms = mod(d.count() * static_cast<common_type>(Period::num) /
static_cast<common_type>(Period::den) * 1000,
1000);
return std::chrono::duration<Rep, std::milli>(static_cast<Rep>(ms));
// We need to compare the duration using the count() method directly
// due to a compiler bug in clang-11 regarding the spaceship operator,
// when -Wzero-as-null-pointer-constant is enabled.
// In clang-12 the bug has been fixed. See
// https://bugs.llvm.org/show_bug.cgi?id=46235 and the reproducible example:
// https://www.godbolt.org/z/Knbb5joYx
return d.count() >= d.zero().count() ? d : -d;
}

template <class Rep, class Period,
FMT_ENABLE_IF(!std::numeric_limits<Rep>::is_signed)>
static constexpr std::chrono::duration<Rep, Period> abs(
std::chrono::duration<Rep, Period> d) {
return d;
}

template <typename Char, typename Rep, typename OutputIt,
Expand Down Expand Up @@ -1630,6 +1650,38 @@ struct chrono_formatter {
out = format_decimal<char_type>(out, n, num_digits).end;
}

template <class Duration> void write_fractional_seconds(Duration d) {
constexpr auto fractional_width =
detail::num_digits(Duration::period::num, Duration::period::den);

using subsecond_precision = std::chrono::duration<
typename std::common_type<typename Duration::rep,
std::chrono::seconds::rep>::type,
std::ratio<1, detail::pow10(fractional_width)>>;
// We could use c++ 17 if constexpr here.
if (std::ratio_less<typename subsecond_precision::period,
std::chrono::seconds::period>::value) {
*out++ = '.';
const auto subseconds =
std::chrono::treat_as_floating_point<
typename subsecond_precision::rep>::value
? (detail::abs(d) -
std::chrono::duration_cast<std::chrono::seconds>(d))
.count()
: std::chrono::duration_cast<subsecond_precision>(
detail::abs(d) -
std::chrono::duration_cast<std::chrono::seconds>(d))
.count();
uint32_or_64_or_128_t<long long> n =
to_unsigned(to_nonnegative_int(subseconds, max_value<long long>()));
int num_digits = detail::count_digits(n);
if (fractional_width > num_digits) {
out = std::fill_n(out, fractional_width - num_digits, '0');
}
out = format_decimal<char_type>(out, n, num_digits).end;
}
}

void write_nan() { std::copy_n("nan", 3, out); }
void write_pinf() { std::copy_n("inf", 3, out); }
void write_ninf() { std::copy_n("-inf", 4, out); }
Expand Down Expand Up @@ -1707,19 +1759,7 @@ struct chrono_formatter {

if (ns == numeric_system::standard) {
write(second(), 2);
#if FMT_SAFE_DURATION_CAST
// convert rep->Rep
using duration_rep = std::chrono::duration<rep, Period>;
using duration_Rep = std::chrono::duration<Rep, Period>;
auto tmpval = fmt_safe_duration_cast<duration_Rep>(duration_rep{val});
#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);
}
write_fractional_seconds(std::chrono::duration<rep, Period>{val});
return;
}
auto time = tm();
Expand Down Expand Up @@ -1748,7 +1788,7 @@ struct chrono_formatter {
on_24_hour_time();
*out++ = ':';
if (handle_nan_inf()) return;
write(second(), 2);
on_second(numeric_system::standard);
}

void on_am_pm() {
Expand Down
47 changes: 42 additions & 5 deletions test/chrono-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -543,15 +543,12 @@ TEST(chrono_test, negative_durations) {
}

TEST(chrono_test, special_durations) {
EXPECT_EQ(
"40.",
fmt::format("{:%S}", std::chrono::duration<double>(1e20)).substr(0, 3));
auto value = fmt::format("{:%S}", std::chrono::duration<double>(1e20));
EXPECT_EQ(value, "40");
auto nan = std::numeric_limits<double>::quiet_NaN();
EXPECT_EQ(
"nan nan nan nan nan:nan nan",
fmt::format("{:%I %H %M %S %R %r}", std::chrono::duration<double>(nan)));
(void)fmt::format("{:%S}",
std::chrono::duration<float, std::atto>(1.79400457e+31f));
EXPECT_EQ(fmt::format("{}", std::chrono::duration<float, std::exa>(1)),
"1Es");
EXPECT_EQ(fmt::format("{}", std::chrono::duration<float, std::atto>(1)),
Expand Down Expand Up @@ -585,4 +582,44 @@ TEST(chrono_test, weekday) {
}
}

TEST(chrono_test, cpp20_duration_subsecond_support) {
using attoseconds = std::chrono::duration<long long, std::atto>;
// Check that 18 digits of subsecond precision are supported.
EXPECT_EQ(fmt::format("{:%S}", attoseconds{999999999999999999}),
"00.999999999999999999");
EXPECT_EQ(fmt::format("{:%S}", attoseconds{673231113420148734}),
"00.673231113420148734");
EXPECT_EQ(fmt::format("{:%S}", attoseconds{-673231113420148734}),
"-00.673231113420148734");
EXPECT_EQ(fmt::format("{:%S}", std::chrono::nanoseconds{13420148734}),
"13.420148734");
EXPECT_EQ(fmt::format("{:%S}", std::chrono::nanoseconds{-13420148734}),
"-13.420148734");
EXPECT_EQ(fmt::format("{:%S}", std::chrono::milliseconds{1234}), "01.234");
{
// Check that {:%H:%M:%S} is equivalent to {:%T}.
auto dur = std::chrono::milliseconds{3601234};
auto formatted_dur = fmt::format("{:%T}", dur);
EXPECT_EQ(formatted_dur, "01:00:01.234");
EXPECT_EQ(fmt::format("{:%H:%M:%S}", dur), formatted_dur);
}
using nanoseconds_dbl = std::chrono::duration<double, std::nano>;
EXPECT_EQ(fmt::format("{:%S}", nanoseconds_dbl{-123456789}), "-00.123456789");
EXPECT_EQ(fmt::format("{:%S}", nanoseconds_dbl{9123456789}), "09.123456789");
// Verify that only the seconds part is extracted and printed.
EXPECT_EQ(fmt::format("{:%S}", nanoseconds_dbl{99123456789}), "39.123456789");
EXPECT_EQ(fmt::format("{:%S}", nanoseconds_dbl{99123000000}), "39.123000000");
{
// Now the hour is printed, and we also test if negative doubles work.
auto dur = nanoseconds_dbl{-99123456789};
auto formatted_dur = fmt::format("{:%T}", dur);
EXPECT_EQ(formatted_dur, "-00:01:39.123456789");
EXPECT_EQ(fmt::format("{:%H:%M:%S}", dur), formatted_dur);
}
// Check that durations with precision greater than std::chrono::seconds have
// fixed precision, and print zeros even if there is no fractional part.
EXPECT_EQ(fmt::format("{:%S}", std::chrono::microseconds{7000000}),
"07.000000");
}

#endif // FMT_STATIC_THOUSANDS_SEPARATOR

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