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Optimize tm formatting #2602

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merged 2 commits into from
Nov 25, 2021
Merged

Optimize tm formatting #2602

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19e3e2f
Use predefined formats for C-locale
phprus Nov 11, 2021
d7b90d7
Add platform-specific 'z' formatter
phprus Nov 13, 2021
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164 changes: 117 additions & 47 deletions include/fmt/chrono.h
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
#include <ctime>
#include <locale>
#include <sstream>
#include <type_traits>

#include "format.h"

Expand Down Expand Up @@ -871,6 +872,22 @@ inline const char* tm_mon_short_name(int mon) {
return mon >= 0 && mon <= 11 ? short_name_list[mon] : "???";
}

template <typename T, typename = void>
struct has_member_data_tm_gmtoff : std::false_type {};
template <typename T>
struct has_member_data_tm_gmtoff<T, void_t<decltype(T::tm_gmtoff)>>
: std::true_type {};

#if defined(_WIN32)
inline void tzset_once() {
static bool init = []() -> bool {
_tzset();
return true;
}();
ignore_unused(init);
}
#endif

template <typename OutputIt, typename Char> class tm_writer {
private:
static constexpr int days_per_week = 7;
Expand Down Expand Up @@ -988,6 +1005,36 @@ template <typename OutputIt, typename Char> class tm_writer {
}
}

void write_utc_offset(long offset) {
if (offset < 0) {
*out_++ = '-';
offset = -offset;
} else {
*out_++ = '+';
}
offset /= 60;
write2(static_cast<int>(offset / 60));
write2(static_cast<int>(offset % 60));
}
void format_utc_offset_impl(std::true_type) {
write_utc_offset(tm_.tm_gmtoff);
}
void format_utc_offset_impl(std::false_type) {
#if defined(_WIN32)
tzset_once();
long offset = 0;
_get_timezone(&offset);
if (tm_.tm_isdst) {
long dstbias = 0;
_get_dstbias(&dstbias);
offset += dstbias;
}
write_utc_offset(-offset);
#else
format_localized('z');
#endif
}

void format_localized(char format, char modifier = 0) {
out_ = write<Char>(out_, tm_, loc_, format, modifier);
}
Expand Down Expand Up @@ -1018,13 +1065,16 @@ template <typename OutputIt, typename Char> class tm_writer {
format_localized('A');
}
void on_dec0_weekday(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('w', 'O');
write1(tm_wday());
if (is_classic_ || ns == numeric_system::standard) return write1(tm_wday());
format_localized('w', 'O');
}
void on_dec1_weekday(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('u', 'O');
auto wday = tm_wday();
write1(wday == 0 ? days_per_week : wday);
if (is_classic_ || ns == numeric_system::standard) {
auto wday = tm_wday();
write1(wday == 0 ? days_per_week : wday);
} else {
format_localized('u', 'O');
}
}

void on_abbr_month() {
Expand Down Expand Up @@ -1091,53 +1141,69 @@ template <typename OutputIt, typename Char> class tm_writer {
out_ = copy_str<Char>(std::begin(buf) + offset, std::end(buf), out_);
}

void on_utc_offset() { format_localized('z'); }
void on_utc_offset() {
format_utc_offset_impl(has_member_data_tm_gmtoff<std::tm>{});
}
void on_tz_name() { format_localized('Z'); }

void on_year(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('Y', 'E');
write_year(tm_year());
if (is_classic_ || ns == numeric_system::standard)
return write_year(tm_year());
format_localized('Y', 'E');
}
void on_short_year(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('y', 'O');
write2(split_year_lower(tm_year()));
if (is_classic_ || ns == numeric_system::standard)
return write2(split_year_lower(tm_year()));
format_localized('y', 'O');
}
void on_offset_year() {
if (is_classic_) return write2(split_year_lower(tm_year()));
format_localized('y', 'E');
}
void on_offset_year() { format_localized('y', 'E'); }

void on_century(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('C', 'E');
auto year = tm_year();
auto upper = year / 100;
if (year >= -99 && year < 0) {
// Zero upper on negative year.
*out_++ = '-';
*out_++ = '0';
} else if (upper >= 0 && upper < 100) {
write2(static_cast<int>(upper));
if (is_classic_ || ns == numeric_system::standard) {
auto year = tm_year();
auto upper = year / 100;
if (year >= -99 && year < 0) {
// Zero upper on negative year.
*out_++ = '-';
*out_++ = '0';
} else if (upper >= 0 && upper < 100) {
write2(static_cast<int>(upper));
} else {
out_ = write<Char>(out_, upper);
}
} else {
out_ = write<Char>(out_, upper);
format_localized('C', 'E');
}
}

void on_dec_month(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('m', 'O');
write2(tm_mon() + 1);
if (is_classic_ || ns == numeric_system::standard)
return write2(tm_mon() + 1);
format_localized('m', 'O');
}

void on_dec0_week_of_year(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('U', 'O');
write2((tm_yday() + days_per_week - tm_wday()) / days_per_week);
if (is_classic_ || ns == numeric_system::standard)
return write2((tm_yday() + days_per_week - tm_wday()) / days_per_week);
format_localized('U', 'O');
}
void on_dec1_week_of_year(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('W', 'O');
auto wday = tm_wday();
write2((tm_yday() + days_per_week -
(wday == 0 ? (days_per_week - 1) : (wday - 1))) /
days_per_week);
if (is_classic_ || ns == numeric_system::standard) {
auto wday = tm_wday();
write2((tm_yday() + days_per_week -
(wday == 0 ? (days_per_week - 1) : (wday - 1))) /
days_per_week);
} else {
format_localized('W', 'O');
}
}
void on_iso_week_of_year(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('V', 'O');
write2(tm_iso_week_of_year());
if (is_classic_ || ns == numeric_system::standard)
return write2(tm_iso_week_of_year());
format_localized('V', 'O');
}

void on_iso_week_based_year() { write_year(tm_iso_week_year()); }
Expand All @@ -1151,32 +1217,36 @@ template <typename OutputIt, typename Char> class tm_writer {
write2(yday % 100);
}
void on_day_of_month(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('d', 'O');
write2(tm_mday());
if (is_classic_ || ns == numeric_system::standard) return write2(tm_mday());
format_localized('d', 'O');
}
void on_day_of_month_space(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('e', 'O');
auto mday = to_unsigned(tm_mday()) % 100;
const char* d2 = digits2(mday);
*out_++ = mday < 10 ? ' ' : d2[0];
*out_++ = d2[1];
if (is_classic_ || ns == numeric_system::standard) {
auto mday = to_unsigned(tm_mday()) % 100;
const char* d2 = digits2(mday);
*out_++ = mday < 10 ? ' ' : d2[0];
*out_++ = d2[1];
} else {
format_localized('e', 'O');
}
}

void on_24_hour(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('H', 'O');
write2(tm_hour());
if (is_classic_ || ns == numeric_system::standard) return write2(tm_hour());
format_localized('H', 'O');
}
void on_12_hour(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('I', 'O');
write2(tm_hour12());
if (is_classic_ || ns == numeric_system::standard)
return write2(tm_hour12());
format_localized('I', 'O');
}
void on_minute(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('M', 'O');
write2(tm_min());
if (is_classic_ || ns == numeric_system::standard) return write2(tm_min());
format_localized('M', 'O');
}
void on_second(numeric_system ns) {
if (ns != numeric_system::standard) return format_localized('S', 'O');
write2(tm_sec());
if (is_classic_ || ns == numeric_system::standard) return write2(tm_sec());
format_localized('S', 'O');
}

void on_12_hour_time() {
Expand Down
7 changes: 7 additions & 0 deletions test/chrono-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,14 @@ std::string system_strftime(const std::string& format, const std::tm* timeptr,
os.imbue(loc);
facet.put(os, os, ' ', timeptr, format.c_str(),
format.c_str() + format.size());
#ifdef _WIN32
// Workaround a bug in older versions of Universal CRT.
auto str = os.str();
if (str == "-0000") str = "+0000";
return str;
#else
return os.str();
#endif
}

FMT_CONSTEXPR std::tm make_tm(int year, int mon, int mday, int hour, int min,
Expand Down
7 changes: 7 additions & 0 deletions test/xchar-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -277,7 +277,14 @@ std::wstring system_wcsftime(const std::wstring& format, const std::tm* timeptr,
os.imbue(loc);
facet.put(os, os, L' ', timeptr, format.c_str(),
format.c_str() + format.size());
#ifdef _WIN32
// Workaround a bug in older versions of Universal CRT.
auto str = os.str();
if (str == L"-0000") str = L"+0000";
return str;
#else
return os.str();
#endif
}

TEST(chrono_test, time_point) {
Expand Down