On Thu, Jun 26, 2025 at 2:52 PM Jonathan Wakely <jwak...@redhat.com> wrote:
> On Thu, 26 Jun 2025 at 13:30, Tomasz Kaminski <tkami...@redhat.com> wrote:
> >
> >
> >
> > On Thu, Jun 26, 2025 at 2:13 PM Tomasz Kaminski <tkami...@redhat.com>
> wrote:
> >>
> >>
> >>
> >> On Thu, Jun 26, 2025 at 2:09 PM Jonathan Wakely <jwak...@redhat.com>
> wrote:
> >>>
> >>> On 26/06/25 11:39 +0200, Tomasz Kamiński wrote:
> >>> >This patch extract calls to _M_locale_fmt and construction of the
> struct tm,
> >>> >from the functions dedicated to each specifier, to main format loop in
> >>> >_M_format_to functions. This removes duplicated code repeated for
> specifiers.
> >>>
> >>> Great, this is exactly what I wanted to do. Removing all the branches
> >>> to call _M_locale_fmt from each of the _M_xxx member functions makes
> >>> them smaller and potentially faster.
> >>>
> >>> >To allow _M_locale_fmt to only be called if localized formatting is
> enabled
> >>> >('L' is present in chrono-format-spec), we provide a implementations
> for
> >>> >locale specific specifiers (%c, %r, %x, %X) that produces the same
> result
> >>> >as locale::classic():
> >>> > * %c is implemented as separate _M_c method
> >>> > * %r is implemented as separate _M_r method
> >>> > * %x is implemented together with %D, as they provide same behavior,
> >>> > * %X is implemented together with %R as _M_R_X, as both of them do
> not include
> >>> > subseconds.
> >>>
> >>> Nice.
> >>>
> >>> >The handling of subseconds was also extracted to _M_subsecs function
> that is
> >>> >used by _M_S and _M_T specifier. The _M_T is now implemented in terms
> of
> >>> >_M_R_X (printing time without subseconds) and _M_subs.
> >>> >
> >>> >The __mod responsible for triggering localized formatting was removed
> from
> >>> >method handling most of specifiers, except:
> >>> > * _M_S (for %S) for which it determines if subseconds should be
> included,
> >>> > * _M_z (for %z) for which it determines if ':' is used as separator.
> >>> >
> >>> > PR libstdc++/110739
> >>> >
> >>> >libstdc++-v3/ChangeLog:
> >>> >
> >>> > * include/bits/chrono_io.h
> (__formatter_chrono::_M_use_locale_fmt):
> >>> > Define.
> >>> > (__formatter_chrono::_M_locale_fmt): Moved to front of the
> class.
> >>> > (__formatter_chrono::_M_format_to): Construct and initialize
> >>> > struct tm and call _M_locale_fmt if needed.
> >>> > (__formatter_chrono::_M_c_r_x_X): Split into separate methods.
> >>> > (__formatter_chrono::_M_c, __formatter_chrono::_M_r): Define.
> >>> > (__formatter_chrono::_M_D): Renamed to _M_D_x.
> >>> > (__formatter_chrono::_M_D_x): Renamed from _M_D.
> >>> > (__formatter_chrono::_M_R_T): Split into _M_R_X and _M_T.
> >>> > (__formatter_chrono::_M_R_X): Extracted from _M_R_T.
> >>> > (__formatter_chrono::_M_T): Define in terms of _M_R_X and
> _M_subsecs.
> >>> > (__formatter_chrono::_M_subsecs): Extracted from _M_S.
> >>> > (__formatter_chrono::_M_S): Replaced __mod with __subs
> argument,
> >>> > removed _M_locale_fmt call, and delegate to _M_subsecs.
> >>> > (__formatter_chrono::_M_C_y_Y, __formatter_chrono::_M_d_e)
> >>> > (__formatter_chrono::_M_H_I, __formatter_chrono::_M_m)
> >>> > (__formatter_chrono::_M_u_w, __formatter_chrono::_M_U_V_W):
> Remove
> >>> > __mod argument and call to _M_locale_fmt.
> >>> >---
> >>> > libstdc++-v3/include/bits/chrono_io.h | 340
> +++++++++++++-------------
> >>> > 1 file changed, 172 insertions(+), 168 deletions(-)
> >>> >
> >>> >diff --git a/libstdc++-v3/include/bits/chrono_io.h
> b/libstdc++-v3/include/bits/chrono_io.h
> >>> >index 35e95906e6a..d451bde722d 100644
> >>> >--- a/libstdc++-v3/include/bits/chrono_io.h
> >>> >+++ b/libstdc++-v3/include/bits/chrono_io.h
> >>> >@@ -906,6 +906,40 @@ namespace __format
> >>> > return __format::__write(std::move(__out), __s);
> >>> > }
> >>> >
> >>> >+ [[__gnu__::__always_inline__]]
> >>> >+ static bool
> >>> >+ _S_localized_spec(_CharT __conv, _CharT __mod)
> >>> >+ {
> >>> >+ switch (__conv)
> >>> >+ {
> >>> >+ case 'c':
> >>> >+ case 'r':
> >>> >+ case 'x':
> >>> >+ case 'X':
> >>> >+ return true;
> >>> >+ case 'z':
> >>> >+ return false;
> >>> >+ default:
> >>> >+ return (bool)__mod;
> >>> >+ };
> >>> >+ }
> >>> >+
> >>> >+ // Use the formatting locale's std::time_put facet to produce
> >>> >+ // a locale-specific representation.
> >>> >+ template<typename _Iter>
> >>> >+ _Iter
> >>> >+ _M_locale_fmt(_Iter __out, const locale& __loc, const struct
> tm& __tm,
> >>> >+ char __fmt, char __mod) const
> >>> >+ {
> >>> >+ basic_ostringstream<_CharT> __os;
> >>> >+ __os.imbue(__loc);
> >>> >+ const auto& __tp = use_facet<time_put<_CharT>>(__loc);
> >>> >+ __tp.put(__os, __os, _S_space, &__tm, __fmt, __mod);
> >>> >+ if (__os)
> >>> >+ __out = _M_write(std::move(__out), __loc, __os.view());
> >>> >+ return __out;
> >>> >+ }
> >>> >+
> >>> > template<typename _Out, typename _FormatContext>
> >>> > _Out
> >>> > _M_format_to(const _ChronoData<_CharT>& __t, _Out __out,
> >>> >@@ -923,6 +957,36 @@ namespace __format
> >>> > return std::move(__out);
> >>> > };
> >>> >
> >>> >+ struct tm __tm{};
> >>> >+ bool __use_locale_fmt = false;
> >>> >+ if (_M_spec._M_localized && _M_spec._M_locale_specific)
> >>> >+ if (__fc.locale() != locale::classic())
> >>> >+ {
> >>> >+ __use_locale_fmt = true;
> >>> >+
> >>> >+ __tm.tm_year = (int)__t._M_year - 1900;
> >>> >+ __tm.tm_yday = __t._M_day_of_year.count();
> >>> >+ __tm.tm_mon = (unsigned)__t._M_month - 1;
> >>> >+ __tm.tm_mday = (unsigned)__t._M_day;
> >>> >+ __tm.tm_wday = __t._M_weekday.c_encoding();
> >>> >+ __tm.tm_hour = __t._M_hours.count();
> >>> >+ __tm.tm_min = __t._M_minutes.count();
> >>> >+ __tm.tm_sec = __t._M_seconds.count();
> >>> >+
> >>> >+ // Some locales use %Z in their %c format but we don't
> want strftime
> >>> >+ // to use the system's local time zone (from
> /etc/localtime or $TZ)
> >>> >+ // as the output for %Z. Setting tm_isdst to -1 says
> there is no
> >>> >+ // time zone info available for the time in __tm.
> >>> >+ __tm.tm_isdst = -1;
> >>> >+
> >>> >+#ifdef _GLIBCXX_USE_STRUCT_TM_TM_ZONE
> >>> >+ // POSIX.1-2024 adds tm.tm_zone which will be used for
> %Z.
> >>> >+ // BSD has had tm_zone since 1987 but as char* so cast
> away const.
> >>> >+ if (__t._M_zone_cstr)
> >>> >+ __tm.tm_zone = const_cast<char*>(__t._M_zone_cstr);
> >>> >+#endif
> >>> >+ }
> >>> >+
> >>> > // Characters to output for "%n", "%t" and "%%" specifiers.
> >>> > constexpr const _CharT* __literals = _GLIBCXX_WIDEN("\n\t%");
> >>> >
> >>> >@@ -932,7 +996,10 @@ namespace __format
> >>> > do
> >>> > {
> >>> > _CharT __c = *__first++;
> >>> >- switch (__c)
> >>> >+ if (__use_locale_fmt && _S_localized_spec(__c, __mod))
> [[unlikely]]
> >>> >+ __out = _M_locale_fmt(std::move(__out), __fc.locale(),
> >>> >+ __tm, __c, __mod);
> >>> >+ else switch (__c)
> >>> > {
> >>> > // %\0 is extension for handling weekday index
> >>> > case '\0':
> >>> >@@ -948,22 +1015,20 @@ namespace __format
> >>> > __out = _M_b_B(__t._M_month, std::move(__out), __fc,
> __c == 'B');
> >>> > break;
> >>> > case 'c':
> >>> >- case 'r':
> >>> >- case 'x':
> >>> >- case 'X':
> >>> >- __out = _M_c_r_x_X(__t, std::move(__out), __fc, __c,
> __mod);
> >>> >+ __out = _M_c(__t, std::move(__out), __fc);
> >>> > break;
> >>> > case 'C':
> >>> > case 'y':
> >>> > case 'Y':
> >>> >- __out = _M_C_y_Y(__t._M_year, std::move(__out),
> __fc, __c, __mod);
> >>> >+ __out = _M_C_y_Y(__t._M_year, std::move(__out),
> __fc, __c);
> >>> > break;
> >>> > case 'd':
> >>> > case 'e':
> >>> >- __out = _M_d_e(__t._M_day, std::move(__out), __fc,
> __c, __mod == 'O');
> >>> >+ __out = _M_d_e(__t._M_day, std::move(__out), __fc,
> __c);
> >>> > break;
> >>> > case 'D':
> >>> >- __out = _M_D(__t, std::move(__out), __fc);
> >>> >+ case 'x':
> >>> >+ __out = _M_D_x(__t, std::move(__out), __fc);
> >>> > break;
> >>> > case 'F':
> >>> > __out = _M_F(__t, std::move(__out), __fc);
> >>> >@@ -974,16 +1039,16 @@ namespace __format
> >>> > break;
> >>> > case 'H':
> >>> > case 'I':
> >>> >- __out = _M_H_I(__t._M_hours, __print_sign(), __fc,
> __c, __mod == 'O');
> >>> >+ __out = _M_H_I(__t._M_hours, __print_sign(), __fc,
> __c);
> >>> > break;
> >>> > case 'j':
> >>> > __out = _M_j(__t, __print_sign(), __fc);
> >>> > break;
> >>> > case 'm':
> >>> >- __out = _M_m(__t._M_month, std::move(__out), __fc,
> __mod == 'O');
> >>> >+ __out = _M_m(__t._M_month, std::move(__out), __fc);
> >>> > break;
> >>> > case 'M':
> >>> >- __out = _M_M(__t._M_minutes, __print_sign(), __fc,
> __mod == 'O');
> >>> >+ __out = _M_M(__t._M_minutes, __print_sign(), __fc);
> >>> > break;
> >>> > case 'p':
> >>> > __out = _M_p(__t._M_hours, std::move(__out), __fc);
> >>> >@@ -994,22 +1059,28 @@ namespace __format
> >>> > case 'Q':
> >>> > __out = _M_Q(__t, __print_sign(), __fc);
> >>> > break;
> >>> >+ case 'r':
> >>> >+ __out = _M_r(__t, __print_sign(), __fc);
> >>> >+ break;
> >>> > case 'R':
> >>> >+ case 'X':
> >>> >+ __out = _M_R_X(__t, __print_sign(), __fc, __c !=
> 'R');
> >>> >+ break;
> >>> > case 'T':
> >>> >- __out = _M_R_T(__t, __print_sign(), __fc, __c ==
> 'T');
> >>> >+ __out = _M_T(__t, __print_sign(), __fc);
> >>> > break;
> >>> >+
> >>> > case 'S':
> >>> >- __out = _M_S(__t, __print_sign(), __fc, __mod ==
> 'O');
> >>> >+ __out = _M_S(__t, __print_sign(), __fc, __mod !=
> 'O');
> >>> > break;
> >>> > case 'u':
> >>> > case 'w':
> >>> >- __out = _M_u_w(__t._M_weekday, std::move(__out),
> __fc, __c, __mod == 'O');
> >>> >+ __out = _M_u_w(__t._M_weekday, std::move(__out),
> __fc, __c);
> >>> > break;
> >>> > case 'U':
> >>> > case 'V':
> >>> > case 'W':
> >>> >- __out = _M_U_V_W(__t, std::move(__out), __fc, __c,
> >>> >- __mod == 'O');
> >>> >+ __out = _M_U_V_W(__t, std::move(__out), __fc, __c);
> >>> > break;
> >>> > case 'z':
> >>> > __out = _M_z(__t._M_zone_offset, std::move(__out),
> __fc, (bool)__mod);
> >>> >@@ -1132,50 +1203,27 @@ namespace __format
> >>> >
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> >- _M_c_r_x_X(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> >- _FormatContext& __ctx, _CharT __conv, _CharT __mod)
> const
> >>> >+ _M_c(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> >+ _FormatContext& __ctx) const
> >>> > {
> >>> >- // %c Locale's date and time representation.
> >>> >- // %Ec Locale's alternate date and time representation.
> >>> >- // %r Locale's 12-hour clock time.
> >>> >- // %x Locale's date rep
> >>> >- // %Ex Locale's alternative date representation.
> >>> >- // %X Locale's time rep
> >>> >- // %EX Locale's alternative time representation.
> >>> >-
> >>> >- using namespace chrono;
> >>> >- struct tm __tm{};
> >>> >-
> >>> >- // Some locales use %Z in their %c format but we don't want
> strftime
> >>> >- // to use the system's local time zone (from /etc/localtime
> or $TZ)
> >>> >- // as the output for %Z. Setting tm_isdst to -1 says there
> is no
> >>> >- // time zone info available for the time in __tm.
> >>> >- __tm.tm_isdst = -1;
> >>> >-
> >>> >-#ifdef _GLIBCXX_USE_STRUCT_TM_TM_ZONE
> >>> >- // POSIX.1-2024 adds tm.tm_zone which will be used for %Z.
> >>> >- // BSD has had tm_zone since 1987 but as char* so cast away
> const.
> >>> >- if (__t._M_zone_cstr)
> >>> >- __tm.tm_zone = const_cast<char*>(__t._M_zone_cstr);
> >>> >-#endif
> >>> >-
> >>> >- __tm.tm_year = (int)__t._M_year - 1900;
> >>> >- __tm.tm_yday = __t._M_day_of_year.count();
> >>> >- __tm.tm_mon = (unsigned)__t._M_month - 1;
> >>> >- __tm.tm_mday = (unsigned)__t._M_day;
> >>> >- __tm.tm_wday = __t._M_weekday.c_encoding();
> >>> >- __tm.tm_hour = __t._M_hours.count();
> >>> >- __tm.tm_min = __t._M_minutes.count();
> >>> >- __tm.tm_sec = __t._M_seconds.count();
> >>> >-
> >>> >- return _M_locale_fmt(std::move(__out), _M_locale(__ctx),
> __tm,
> >>> >- __conv, __mod);
> >>> >+ // %c Locale's date and time representation, for C-locale:
> %a %b %e %T %Y
> >>> >+ // %Ec Locale's alternate date and time representation, for
> C-locale same as above
> >>> >+
> >>> >+ __out = _M_a_A(__t._M_weekday, std::move(__out), __ctx,
> false);
> >>> >+ *__out = _S_space;
> >>> >+ __out = _M_b_B(__t._M_month, std::move(++__out), __ctx,
> false);
> >>> >+ *__out = _S_space;
> >>> >+ __out = _M_d_e(__t._M_day, std::move(++__out), __ctx, 'e');
> >>> >+ *__out = _S_space;
> >>> >+ __out = _M_R_X(__t, std::move(++__out), __ctx, true);
> >>> >+ *__out = _S_space;
> >>> >+ return _M_C_y_Y(__t._M_year, std::move(__out), __ctx, 'Y');
> >>> > }
> >>> >
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> > _M_C_y_Y(chrono::year __y, typename _FormatContext::iterator
> __out,
> >>> >- _FormatContext& __ctx, _CharT __conv, _CharT __mod =
> 0) const
> >>> >+ _FormatContext& __ctx, _CharT __conv) const
> >>> > {
> >>> > // %C Year divided by 100 using floored division.
> >>> > // %EC Locale's alternative preresentation of the century
> (era name).
> >>> >@@ -1185,15 +1233,6 @@ namespace __format
> >>> > // %Y Year as a decimal number.
> >>> > // %EY Locale's alternative full year representation.
> >>> >
> >>> >- if (__mod && _M_spec._M_localized) [[unlikely]]
> >>> >- if (auto __loc = __ctx.locale(); __loc !=
> locale::classic())
> >>> >- {
> >>> >- struct tm __tm{};
> >>> >- __tm.tm_year = (int)__y - 1900;
> >>> >- return _M_locale_fmt(std::move(__out), __loc, __tm,
> >>> >- __conv, __mod);
> >>> >- }
> >>> >-
> >>> > int __yi = (int)__y;
> >>> > const bool __is_neg = __yi < 0;
> >>> > __yi = __builtin_abs(__yi);
> >>> >@@ -1235,9 +1274,13 @@ namespace __format
> >>> >
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> >- _M_D(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> >- _FormatContext&) const
> >>> >+ _M_D_x(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> >+ _FormatContext&) const
> >>> > {
> >>> >+ // %D Equivalent to %m/%d/%y
> >>> >+ // %x Locale's date rep, for C-locale: %m/%d/%y
> >>> >+ // %Ex Locale's alternative date representation, for
> C-locale same as above
> >>> >+
> >>> > auto __di = (unsigned)__t._M_day;
> >>> > auto __mi = (unsigned)__t._M_month;
> >>> > auto __yi = __builtin_abs((int)__t._M_year) % 100;
> >>> >@@ -1267,7 +1310,7 @@ namespace __format
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> > _M_d_e(chrono::day __d, typename _FormatContext::iterator
> __out,
> >>> >- _FormatContext& __ctx, _CharT __conv, bool __mod =
> false) const
> >>> >+ _FormatContext& __ctx, _CharT __conv) const
> >>> > {
> >>> > // %d The day of month as a decimal number.
> >>> > // %Od Locale's alternative representation.
> >>> >@@ -1276,15 +1319,6 @@ namespace __format
> >>> >
> >>> > unsigned __i = (unsigned)__d;
> >>> >
> >>> >- if (__mod && _M_spec._M_localized) [[unlikely]]
> >>> >- if (auto __loc = __ctx.locale(); __loc !=
> locale::classic())
> >>> >- {
> >>> >- struct tm __tm{};
> >>> >- __tm.tm_mday = __i;
> >>> >- return _M_locale_fmt(std::move(__out), __loc, __tm,
> >>> >- (char)__conv, 'O');
> >>> >- }
> >>> >-
> >>> > _CharT __buf[3];
> >>> > auto __sv = _S_str_d2(__buf, __i);
> >>> > if (__conv == _CharT('e') && __i < 10)
> >>> >@@ -1360,7 +1394,7 @@ namespace __format
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> > _M_H_I(chrono::hours __h, typename _FormatContext::iterator
> __out,
> >>> >- _FormatContext& __ctx, _CharT __conv, bool __mod =
> false) const
> >>> >+ _FormatContext& __ctx, _CharT __conv) const
> >>> > {
> >>> > // %H The hour (24-hour clock) as a decimal number.
> >>> > // %OH Locale's alternative representation.
> >>> >@@ -1369,15 +1403,6 @@ namespace __format
> >>> >
> >>> > int __i = __h.count();
> >>> >
> >>> >- if (__mod && _M_spec._M_localized) [[unlikely]]
> >>> >- if (auto __loc = __ctx.locale(); __loc !=
> locale::classic())
> >>> >- {
> >>> >- struct tm __tm{};
> >>> >- __tm.tm_hour = __i;
> >>> >- return _M_locale_fmt(std::move(__out), __loc, __tm,
> >>> >- (char)__conv, 'O');
> >>> >- }
> >>> >-
> >>> > if (__conv == _CharT('I'))
> >>> > {
> >>> > __i %= 12;
> >>> >@@ -1409,22 +1434,13 @@ namespace __format
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> > _M_m(chrono::month __m, typename _FormatContext::iterator
> __out,
> >>> >- _FormatContext& __ctx, bool __mod) const
> >>> >+ _FormatContext& __ctx) const
> >>> > {
> >>> > // %m month as a decimal number.
> >>> > // %Om Locale's alternative representation.
> >>> >
> >>> > auto __i = (unsigned)__m;
> >>> >
> >>> >- if (__mod && _M_spec._M_localized) [[unlikely]] // %Om
> >>> >- if (auto __loc = __ctx.locale(); __loc !=
> locale::classic())
> >>> >- {
> >>> >- struct tm __tm{};
> >>> >- __tm.tm_mon = __i - 1;
> >>> >- return _M_locale_fmt(std::move(__out), __loc, __tm,
> >>> >- 'm', 'O');
> >>> >- }
> >>> >-
> >>> > _CharT __buf[3];
> >>> > return __format::__write(std::move(__out), _S_str_d2(__buf,
> __i));
> >>> > }
> >>> >@@ -1432,22 +1448,12 @@ namespace __format
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> > _M_M(chrono::minutes __m, typename _FormatContext::iterator
> __out,
> >>> >- _FormatContext& __ctx, bool __mod) const
> >>> >+ _FormatContext& __ctx) const
> >>> > {
> >>> > // %M The minute as a decimal number.
> >>> > // %OM Locale's alternative representation.
> >>> >
> >>> > auto __i = __m.count();
> >>> >-
> >>> >- if (__mod && _M_spec._M_localized) [[unlikely]] // %OM
> >>> >- if (auto __loc = __ctx.locale(); __loc !=
> locale::classic())
> >>> >- {
> >>> >- struct tm __tm{};
> >>> >- __tm.tm_min = __i;
> >>> >- return _M_locale_fmt(std::move(__out), __loc, __tm,
> >>> >- 'M', 'O');
> >>> >- }
> >>> >-
> >>> > return __format::__write(std::move(__out),
> _S_two_digits(__i));
> >>> > }
> >>> >
> >>> >@@ -1488,17 +1494,42 @@ namespace __format
> >>> >
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> >- _M_R_T(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> >+ _M_r(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> >+ _FormatContext& __ctx) const
> >>> >+ {
> >>> >+ // %r Locale's 12-hour clock time, for C-locale: %I:%M:%S %p
> >>> >+ auto __hi = __t._M_hours.count() % 12;
> >>> >+ if (__hi == 0)
> >>> >+ __hi = 12;
> >>> >+
> >>> >+ _CharT __buf[9];
> >>> >+ __buf[2] = _S_colon;
> >>> >+ __buf[5] = _S_colon;
> >>> >+ __buf[8] = _S_space;
> >>> >+ _S_fill_two_digits(__buf, __hi);
> >>> >+ _S_fill_two_digits(__buf + 3, __t._M_minutes.count());
> >>> >+ _S_fill_two_digits(__buf + 6, __t._M_seconds.count());
> >>> >+
> >>> >+ __string_view __sv(__buf, 9);
> >>> >+ __out = __format::__write(std::move(__out), __sv);
> >>> >+ return _M_p(__t._M_hours, std::move(__out), __ctx);
> >>> >+ }
> >>> >+
> >>> >+ template<typename _FormatContext>
> >>> >+ typename _FormatContext::iterator
> >>> >+ _M_R_X(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> > _FormatContext& __ctx, bool __secs) const
> >>> > {
> >>> >- // %R Equivalent to %H:%M
> >>> >- // %T Equivalent to %H:%M:%S
> >>> >+ // %R Equivalent to %H:%M
> >>> >+ // %X Locale's time rep, for C-locale: %H:%M:%S (without
> subseconds)
> >>> >+ // %EX Locale's alternative time representation, for
> C-locale same as above
> >>> >+
> >>> > auto __hi = __t._M_hours.count();
> >>> >
> >>> >- _CharT __buf[6];
> >>> >+ _CharT __buf[8];
> >>> > __buf[2] = _S_colon;
> >>> > __buf[5] = _S_colon;
> >>> >- __string_view __sv(__buf, 5 + __secs);
> >>> >+ __string_view __sv(__buf, 8);
> >>> >
> >>> > if (__hi >= 100) [[unlikely]]
> >>> > {
> >>> >@@ -1509,39 +1540,39 @@ namespace __format
> >>> > _S_fill_two_digits(__buf, __hi);
> >>> >
> >>> > _S_fill_two_digits(__buf + 3, __t._M_minutes.count());
> >>> >- __out = __format::__write(std::move(__out), __sv);
> >>> > if (__secs)
> >>> >- __out = _M_S(__t, std::move(__out), __ctx);
> >>> >- return __out;
> >>> >+ _S_fill_two_digits(__buf + 6, __t._M_seconds.count());
> >>> >+ else
> >>> >+ __sv.remove_suffix(3);
> >>> >+
> >>> >+ return __format::__write(std::move(__out), __sv);
> >>> > }
> >>> >
> >>> > template<typename _FormatContext>
> >>> > typename _FormatContext::iterator
> >>> > _M_S(const _ChronoData<_CharT>& __t, typename
> _FormatContext::iterator __out,
> >>> >- _FormatContext& __ctx, bool __mod = false) const
> >>> >+ _FormatContext& __ctx, bool __subs = true) const
> >>> > {
> >>> >- // %S Seconds as a decimal number.
> >>>
> >>> Doesn't this function still handle %S formats? Should this comment be
> kept?
> >>
> >> Yes, it gets called to handle '%S' in the big switch. It is no longer
> called by _M_T, which calls _M_subsecs
> >> directly.
> >
> > Ah, you are referring to 'OS'. Yes, it is still-handled here, if the
> format is not localized, or the locale is the same
> > as classic. The effect is that we do not print subseconds.
>
> What I mean is that the _M_S function handles both %S and %OS, but you
> remove the comment about %S which suggests to me that it only handles
> %OS now (but that's not correct).
>
> Should the first comment line be restored?
>
Yes, I did that already locally, and forgot to mention it. I removed it by
accident.
