libstdc++: Format %a/%A/%b/%h/%B/%p without using locale::classic [PR110739]

With changes r16-2063-g8ad5968a8dcb47 the _M_a_A, _M_b_B and _M_p functions
are called only if the locale is equal to the locale::classic(), for which
the behavior is know. This patch changes they implementation, so instead of
reffering to __timepunct facet members, they use hardcoded list of English
weekday, months names. Only one list is needed, as in case of locale::classic()
abbreviated name corresponds to first tree letters of the full name.

For _M_p, _M_r we use a new _M_fill_ampm helper, that fills provided buffer
with "AM"/"PM" depending on the hours value.

In _M_S we no longer guard querying of numpuct facet, with check that requires
potentially equally expensive construction of locale::classic. We also mark
localized path as unlikely.

The _M_locale method is no longer used in __formatter_chrono, and thus was
moved to __formatter_duration.

	PR libstdc++/110739

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (__formatter_chrono::_S_weekdays)
	(__formatter_chrono::_S_months, __formatter_chrono::_S_fill_ampm):
	Define.
	(__formatter_chrono::_M_format_to): Do not pass context parameter
	to functions listed below.
	(__formatter_chrono::_M_a_A, __formatter_chrono::_M_b_B): Implement
	using harcoded list of names, and remove format context parameter.
	(__formatter_chrono::_M_p, __formatter_chrono::_M_r): Implement
	using _S_fill_ampm.
	(__formatter_chrono::_M_c): Removed format context parameter.
	(__formatter_chrono::_M_subsecs): Call __ctx.locale() directly,
	instead of _M_locale and do not compare with locale::classic().
	Add [[unlikely]] attributes.
	(__formatter_chrono::_M_locale): Move to __formatter_duration.
	(__formatter_duration::_M_locale): Moved from __formatter_chrono.

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index 75ee7e818b2f95c225799e84a949e2f414569a74..fe3c9126749732f7dbae4fa2862d21a1ade12a50 100644 (file)
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -881,16 +881,32 @@ namespace __format
       _S_empty_fs()
       { return _Runtime_format_string<_CharT>(_S_empty_spec); }
 
-      // Return the formatting locale.
-      template<typename _FormatContext>
-       std::locale
-       _M_locale(_FormatContext& __fc) const
-       {
-         if (!_M_spec._M_localized)
-           return std::locale::classic();
-         else
-           return __fc.locale();
-       }
+      static constexpr const _CharT* _S_weekdays[]
+      {
+       _GLIBCXX_WIDEN("Sunday"),
+       _GLIBCXX_WIDEN("Monday"),
+       _GLIBCXX_WIDEN("Tuesday"),
+       _GLIBCXX_WIDEN("Wednesday"),
+       _GLIBCXX_WIDEN("Thursday"),
+       _GLIBCXX_WIDEN("Friday"),
+       _GLIBCXX_WIDEN("Saturday"),
+      };
+
+      static constexpr const _CharT* _S_months[]
+      {
+       _GLIBCXX_WIDEN("January"),
+       _GLIBCXX_WIDEN("February"),
+       _GLIBCXX_WIDEN("March"),
+       _GLIBCXX_WIDEN("April"),
+       _GLIBCXX_WIDEN("May"),
+       _GLIBCXX_WIDEN("June"),
+       _GLIBCXX_WIDEN("July"),
+       _GLIBCXX_WIDEN("August"),
+       _GLIBCXX_WIDEN("September"),
+       _GLIBCXX_WIDEN("October"),
+       _GLIBCXX_WIDEN("November"),
+       _GLIBCXX_WIDEN("December"),
+      };
 
     private:
       template<typename _OutIter>
@@ -1051,15 +1067,15 @@ namespace __format
                  break;
                case 'a':
                case 'A':
-                 __out = _M_a_A(__t._M_weekday, std::move(__out), __fc, __c == 'A');
+                 __out = _M_a_A(__t._M_weekday, std::move(__out), __c == 'A');
                  break;
                case 'b':
                case 'h':
                case 'B':
-                 __out = _M_b_B(__t._M_month, std::move(__out), __fc, __c == 'B');
+                 __out = _M_b_B(__t._M_month, std::move(__out), __c == 'B');
                  break;
                case 'c':
-                 __out = _M_c(__t, std::move(__out), __fc);
+                 __out = _M_c(__t, std::move(__out));
                  break;
                case 'C':
                case 'y':
@@ -1095,7 +1111,7 @@ namespace __format
                  __out = _M_M(__t._M_minutes, __print_sign());
                  break;
                case 'p':
-                 __out = _M_p(__t._M_hours, std::move(__out), __fc);
+                 __out = _M_p(__t._M_hours, std::move(__out));
                  break;
                case 'q':
                  __out = _M_q(__t._M_unit_suffix, std::move(__out));
@@ -1104,7 +1120,7 @@ namespace __format
                  __out = _M_Q(__t, __print_sign(), __fc);
                  break;
                case 'r':
-                 __out = _M_r(__t, __print_sign(), __fc);
+                 __out = _M_r(__t, __print_sign());
                  break;
                case 'R':
                case 'X':
@@ -1183,10 +1199,9 @@ namespace __format
          return std::move(__out);
        }
 
-      template<typename _OutIter, typename _FormatContext>
+      template<typename _OutIter>
        _OutIter
-       _M_a_A(chrono::weekday __wd, _OutIter __out,
-              _FormatContext& __ctx, bool __full) const
+       _M_a_A(chrono::weekday __wd, _OutIter __out, bool __full) const
        {
          // %a Locale's abbreviated weekday name.
          // %A Locale's full weekday name.
@@ -1199,21 +1214,15 @@ namespace __format
                        __string_view(_GLIBCXX_WIDEN(" is not a valid weekday")));
            }
 
-         locale __loc = _M_locale(__ctx);
-         const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
-         const _CharT* __days[7];
-         if (__full)
-           __tp._M_days(__days);
-         else
-           __tp._M_days_abbreviated(__days);
-         __string_view __str(__days[__wd.c_encoding()]);
-         return _M_write(std::move(__out), __loc, __str);
+         __string_view __str = _S_weekdays[__wd.c_encoding()];
+         if (!__full)
+           __str = __str.substr(0, 3);
+         return __format::__write(std::move(__out), __str);
        }
 
-      template<typename _OutIter, typename _FormatContext>
+      template<typename _OutIter>
        _OutIter
-       _M_b_B(chrono::month __m, _OutIter __out,
-              _FormatContext& __ctx, bool __full) const
+       _M_b_B(chrono::month __m, _OutIter __out, bool __full) const
        {
          // %b Locale's abbreviated month name.
          // %B Locale's full month name.
@@ -1226,28 +1235,22 @@ namespace __format
                        __string_view(_GLIBCXX_WIDEN(" is not a valid month")));
            }
 
-         locale __loc = _M_locale(__ctx);
-         const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
-         const _CharT* __months[12];
-         if (__full)
-           __tp._M_months(__months);
-         else
-           __tp._M_months_abbreviated(__months);
-         __string_view __str(__months[(unsigned)__m - 1]);
-         return _M_write(std::move(__out), __loc, __str);
+         __string_view __str = _S_months[(unsigned)__m - 1];
+         if (!__full)
+           __str = __str.substr(0, 3);
+         return __format::__write(std::move(__out), __str);
        }
 
-      template<typename _OutIter, typename _FormatContext>
+      template<typename _OutIter>
        _OutIter
-       _M_c(const _ChronoData<_CharT>& __t, _OutIter __out,
-            _FormatContext& __ctx) const
+       _M_c(const _ChronoData<_CharT>& __t, _OutIter __out) const
        {
          // %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 = _M_a_A(__t._M_weekday, std::move(__out), false);
          *__out = _S_space;
-         __out = _M_b_B(__t._M_month, std::move(++__out), __ctx, false);
+         __out = _M_b_B(__t._M_month, std::move(++__out), false);
          *__out = _S_space;
          __out = _M_d_e(__t._M_day, std::move(++__out), 'e');
          *__out = _S_space;
@@ -1489,20 +1492,15 @@ namespace __format
          return __format::__write(std::move(__out), _S_two_digits(__i));
        }
 
-      template<typename _OutIter, typename _FormatContext>
+      template<typename _OutIter>
        _OutIter
-       _M_p(chrono::hours __h, _OutIter __out, _FormatContext& __ctx) const
+       _M_p(chrono::hours __h, _OutIter __out) const
        {
          // %p The locale's equivalent of the AM/PM designations.
-         auto __hi =  __h.count();
-         if (__hi >= 24) [[unlikely]]
-           __hi %= 24;
-
-         locale __loc = _M_locale(__ctx);
-         const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
-         const _CharT* __ampm[2];
-         __tp._M_am_pm(__ampm);
-         return _M_write(std::move(__out), __loc, __ampm[__hi >= 12]);
+
+         _CharT __buf[2];
+         _S_fill_ampm(__buf, __h);
+         return __format::__write(std::move(__out), __string_view(__buf, 2));
        }
 
       template<typename _OutIter>
@@ -1522,27 +1520,25 @@ namespace __format
          return std::vformat_to(std::move(__out), _S_empty_spec, __t._M_ereps);
        }
 
-      template<typename _OutIter, typename _FormatContext>
+      template<typename _OutIter>
        _OutIter
-       _M_r(const _ChronoData<_CharT>& __t, _OutIter __out,
-            _FormatContext& __ctx) const
+       _M_r(const _ChronoData<_CharT>& __t, _OutIter __out) 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];
+         _CharT __buf[11];
          __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());
+         _S_fill_ampm(__buf + 9, __t._M_hours);
 
-         __string_view __sv(__buf, 9);
-         __out = __format::__write(std::move(__out), __sv);
-         return _M_p(__t._M_hours, std::move(__out), __ctx);
+         return __format::__write(std::move(__out), __string_view(__buf, 11));
        }
 
       template<typename _OutIter>
@@ -1606,9 +1602,9 @@ namespace __format
            return __out;
 
          _CharT __dot = _S_dot;
-         if (_M_spec._M_localized)
-           if (auto __loc = __ctx.locale(); __loc != locale::classic())
+         if (_M_spec._M_localized) [[unlikely]]
            {
+             auto __loc = __ctx.locale();
              const auto& __np = use_facet<numpunct<_CharT>>(__loc);
              __dot = __np.decimal_point();
            }
@@ -1618,8 +1614,8 @@ namespace __format
          if (_M_spec._M_floating_point_rep)
            {
              _Str_sink<_CharT> __sink;
-             if (_M_spec._M_localized && _M_spec._M_custom_rep)
-                std::vformat_to(__sink.out(), _M_locale(__ctx),
+             if (_M_spec._M_localized && _M_spec._M_custom_rep) [[unlikely]]
+                std::vformat_to(__sink.out(), __ctx.locale(),
                                 _GLIBCXX_WIDEN("{1:0.{2}Lf}"), __t._M_ereps);
              else
                 std::vformat_to(__sink.out(),
@@ -1778,6 +1774,20 @@ namespace __format
        __buf[1] = __sv[1];
       }
 
+      // Fills __buf[0] and __buf[1] with "AM", "PM" depending on __h.
+      [[__gnu__::__always_inline__]]
+      static void
+      _S_fill_ampm(_CharT* __buf, chrono::hours __h)
+      {
+       auto __hi =  __h.count();
+       if (__hi >= 24) [[unlikely]]
+         __hi %= 24;
+
+       constexpr const _CharT* __apm = _GLIBCXX_WIDEN("APM");
+       __buf[0] = __apm[__hi >= 12];
+       __buf[1] = __apm[2];
+      }
+
       // Returns decimal representation of __n.
       // Returned string_view may point to __buf.
       [[__gnu__::__always_inline__]]
@@ -1879,7 +1889,6 @@ namespace __format
        };
 
       using __formatter_chrono<_CharT>::__formatter_chrono;
-      using __formatter_chrono<_CharT>::_M_locale;
       using __formatter_chrono<_CharT>::_M_spec;
 
       template<typename _Duration, typename _ParseContext>
@@ -1909,6 +1918,17 @@ namespace __format
          return __res;
        }
 
+      // Return the formatting locale.
+      template<typename _FormatContext>
+       std::locale
+       _M_locale(_FormatContext& __fc) const
+       {
+         if (!_M_spec._M_localized)
+           return std::locale::classic();
+         else
+           return __fc.locale();
+       }
+
       // Format duration for empty chrono-specs, e.g. "{}" (C++20 [time.format] p6).
       template<typename _Rep, typename _Period, typename _FormatContext>
        typename _FormatContext::iterator