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Add precision modifier for seconds in chrono format #3148

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merged 7 commits into from
Nov 2, 2022
Merged

Add precision modifier for seconds in chrono format #3148

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85a4cef
Reuse precision modifier in seconds specification
Sep 28, 2022
21a828c
Apply clang-format
Oct 20, 2022
6ecde30
Make write_fractional_seconds more readable
Oct 21, 2022
e74bc99
Add alias for typename Duration::rep
Oct 26, 2022
54fa95f
Fixes
Nov 2, 2022
e30efa7
Fix build: make n unsigned properly
Nov 2, 2022
5408dd1
Merge write_fractional_seconds call
SappyJoy Nov 2, 2022
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102 changes: 87 additions & 15 deletions include/fmt/chrono.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1056,31 +1056,91 @@ void write_fractional_seconds(OutputIt& out, Duration d) {
}
}

template <typename Char, typename OutputIt, typename Duration>
void write_fractional_seconds(OutputIt& out, Duration d, int precision) {
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Let's merge this overload with the one above to reduce code duplication.

constexpr auto num_fractional_digits =
count_fractional_digits<Duration::period::num,
Duration::period::den>::value;

using subsecond_precision = std::chrono::duration<
typename std::common_type<typename Duration::rep,
std::chrono::seconds::rep>::type,
std::ratio<1, detail::pow10(num_fractional_digits)>>;
if (precision > 0) {
*out++ = '.';
auto fractional =
detail::abs(d) - std::chrono::duration_cast<std::chrono::seconds>(d);
auto subseconds =
std::chrono::treat_as_floating_point<
typename subsecond_precision::rep>::value
? fractional.count()
: std::chrono::duration_cast<subsecond_precision>(fractional)
.count();
uint32_or_64_or_128_t<long long> n =
to_unsigned(to_nonnegative_int(subseconds, max_value<long long>()));
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Can subseconds be negative?

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@SappyJoy SappyJoy Nov 2, 2022 •
edited
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It's nonnegative because fractional is nonnegative:

const auto fractional = detail::abs(d) - std::chrono::duration_cast<std::chrono::seconds>(d);

But subseconds can be signed or unsigned and to_unsigned raises error if argument is unsigned, so i'll make static_cast.

int num_digits = detail::count_digits(n);
int zeroes =
std::min(std::max(0, num_fractional_digits - num_digits), precision);
if (num_fractional_digits > num_digits) out = std::fill_n(out, zeroes, '0');
int remaining = precision - zeroes;
if (remaining < num_digits) {
n /= to_unsigned(detail::pow10(to_unsigned(num_digits - remaining)));
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, remaining, '0');
}
}

// Format subseconds which are given as a floating point type with an appropiate
// number of digits. We cannot pass the Duration here, as we explicitly need to
// pass the Rep value in the chrono_formatter.
template <typename Duration>
void write_floating_seconds(memory_buffer& buf, Duration duration) {
FMT_ASSERT(std::is_floating_point<typename Duration::rep>::value, "");
using Rep = typename Duration::rep;
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nit: Rep -> rep to follow naming conventions

FMT_ASSERT(std::is_floating_point<Rep>::value, "");
auto num_fractional_digits =
count_fractional_digits<Duration::period::num,
Duration::period::den>::value;
// For non-integer values, we ensure at least 6 digits to get microsecond
// precision.
auto val = duration.count();
if (num_fractional_digits < 6 &&
static_cast<typename Duration::rep>(std::round(val)) != val)
static_cast<Rep>(std::round(val)) != val)
num_fractional_digits = 6;

format_to(
std::back_inserter(buf), runtime("{:.{}f}"),
std::fmod(val *
static_cast<typename Duration::rep>(Duration::period::num) /
static_cast<typename Duration::rep>(Duration::period::den),
static_cast<typename Duration::rep>(60)),
static_cast<Rep>(Duration::period::num) /
static_cast<Rep>(Duration::period::den),
static_cast<Rep>(60)),
num_fractional_digits);
}

template <typename Duration>
void write_floating_seconds(memory_buffer& buf, Duration duration,
int precision) {
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Similarly, let's merge the two write_floating_seconds overloads.

using Rep = typename Duration::rep;
if (precision < 0) {
write_floating_seconds(buf, duration);
return;
}

FMT_ASSERT(std::is_floating_point<Rep>::value, "");
auto val = duration.count();

format_to(
std::back_inserter(buf), runtime("{:.{}f}"),
std::fmod(val *
static_cast<Rep>(Duration::period::num) /
static_cast<Rep>(Duration::period::den),
static_cast<Rep>(60)),
precision);
}

template <typename OutputIt, typename Char,
typename Duration = std::chrono::seconds>
class tm_writer {
Expand Down Expand Up @@ -1518,6 +1578,9 @@ class tm_writer {
};

struct chrono_format_checker : null_chrono_spec_handler<chrono_format_checker> {
bool is_floating_point = false;
bool has_precision = false;
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We only need one flag for the condition has_precision && !is_floating_point, something like has_precision_integral.


FMT_NORETURN void unsupported() { FMT_THROW(format_error("no date")); }

template <typename Char>
Expand All @@ -1530,7 +1593,11 @@ struct chrono_format_checker : null_chrono_spec_handler<chrono_format_checker> {
FMT_CONSTEXPR void on_24_hour_time() {}
FMT_CONSTEXPR void on_iso_time() {}
FMT_CONSTEXPR void on_am_pm() {}
FMT_CONSTEXPR void on_duration_value() {}
FMT_CONSTEXPR void on_duration_value() const {
if (has_precision && !is_floating_point) {
FMT_THROW(format_error("precision not allowed for this argument type"));
}
}
FMT_CONSTEXPR void on_duration_unit() {}
};

Expand Down Expand Up @@ -1831,14 +1898,20 @@ struct chrono_formatter {
if (ns == numeric_system::standard) {
if (std::is_floating_point<rep>::value) {
auto buf = memory_buffer();
write_floating_seconds(buf, std::chrono::duration<rep, Period>(val));
write_floating_seconds(buf, std::chrono::duration<rep, Period>(val),
precision);
if (negative) *out++ = '-';
if (buf.size() < 2 || buf[1] == '.') *out++ = '0';
out = std::copy(buf.begin(), buf.end(), out);
} else {
write(second(), 2);
write_fractional_seconds<char_type>(
out, std::chrono::duration<rep, Period>(val));
if (precision >= 0) {
write_fractional_seconds<char_type>(
out, std::chrono::duration<rep, Period>(val), precision);
} else {
write_fractional_seconds<char_type>(
out, std::chrono::duration<rep, Period>(val));
}
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Now that write_fractional_seconds overloads have been merged, the if statement is no longer needed. You can just call

write_fractional_seconds<char_type>(
              out, std::chrono::duration<rep, Period>(val), precision);

}
return;
}
Expand Down Expand Up @@ -1999,18 +2072,17 @@ struct formatter<std::chrono::duration<Rep, Period>, Char> {
if (begin == end) return {begin, begin};
begin = detail::parse_width(begin, end, handler);
if (begin == end) return {begin, begin};
auto checker = detail::chrono_format_checker();
checker.is_floating_point = std::is_floating_point<Rep>::value;
if (*begin == '.') {
if (std::is_floating_point<Rep>::value)
begin = detail::parse_precision(begin, end, handler);
else
handler.on_error("precision not allowed for this argument type");
checker.has_precision = true;
begin = detail::parse_precision(begin, end, handler);
}
if (begin != end && *begin == 'L') {
++begin;
localized = true;
}
end = detail::parse_chrono_format(begin, end,
detail::chrono_format_checker());
end = detail::parse_chrono_format(begin, end, checker);
return {begin, end};
}

Expand Down
19 changes: 18 additions & 1 deletion test/chrono-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -466,7 +466,7 @@ TEST(chrono_test, format_default_fp) {

TEST(chrono_test, format_precision) {
EXPECT_THROW_MSG(
(void)fmt::format(runtime("{:.2}"), std::chrono::seconds(42)),
(void)fmt::format(runtime("{:.2%Q}"), std::chrono::seconds(42)),
fmt::format_error, "precision not allowed for this argument type");
EXPECT_EQ("1ms", fmt::format("{:.0}", dms(1.234)));
EXPECT_EQ("1.2ms", fmt::format("{:.1}", dms(1.234)));
Expand Down Expand Up @@ -611,12 +611,28 @@ TEST(chrono_test, cpp20_duration_subsecond_support) {
EXPECT_EQ(fmt::format("{:%S}", std::chrono::nanoseconds{-13420148734}),
"-13.420148734");
EXPECT_EQ(fmt::format("{:%S}", std::chrono::milliseconds{1234}), "01.234");
// Check subsecond presision modifier.
EXPECT_EQ(fmt::format("{:.6%S}", std::chrono::nanoseconds{1234}),
"00.000001");
EXPECT_EQ(fmt::format("{:.18%S}", std::chrono::nanoseconds{1234}),
"00.000001234000000000");
EXPECT_EQ(fmt::format("{:.{}%S}", std::chrono::nanoseconds{1234}, 6),
"00.000001");
EXPECT_EQ(fmt::format("{:.6%S}", std::chrono::milliseconds{1234}),
"01.234000");
EXPECT_EQ(fmt::format("{:.6%S}", std::chrono::milliseconds{-1234}),
"-01.234000");
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");
EXPECT_EQ(fmt::format("{:.8%S}", dms(1.234)), "00.00123400");
{
// 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);
EXPECT_EQ(fmt::format("{:.6%H:%M:%S}", dur), "01:00:01.234000");
}
using nanoseconds_dbl = std::chrono::duration<double, std::nano>;
EXPECT_EQ(fmt::format("{:%S}", nanoseconds_dbl{-123456789}), "-00.123456789");
Expand All @@ -630,6 +646,7 @@ TEST(chrono_test, cpp20_duration_subsecond_support) {
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);
EXPECT_EQ(fmt::format("{:.3%H:%M:%S}", dur), "-00:01:39.123");
}
// Check that durations with precision greater than std::chrono::seconds have
// fixed precision, and print zeros even if there is no fractional part.
Expand Down