On Wed, May 7, 2025 at 1:01 PM Tomasz Kamiński <tkami...@redhat.com> wrote:
> Formatting code is extracted to _M_format_to function, that produced output
> to specified iterator. This function is now invoked either with __fc.out()
> directly (if width is not specified) or _Padding_sink::out().
>
> This avoid formatting to temporary string if no padding is requested,
> and minimize allocations otherwise. For more details see commit message of
> r16-142-g01e5ef3e8b91288f5d387a27708f9f8979a50edf.
>
> This should not increase number of instantiations, as implementation only
> produce basis_format_context with _Sink_iter as iterator, which is also
> _Padding_sink iterator.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/chrono_io.h (__formatter_chrono::_M_format_to):
> Extracted from _M_format.
> (__formatter_chrono::_M_format): Use _Padding_sink and delegate
> to _M_format_to.
> ---
> I have checked that there are no other calls to out() in this file,
> so _M_format_to uses only __out, and not iterator from __fc.
> Testing on x86_64-linux. OK for trunk?
>
All test passed.
>
> libstdc++-v3/include/bits/chrono_io.h | 55 ++++++++++-----------------
> 1 file changed, 20 insertions(+), 35 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/chrono_io.h
> b/libstdc++-v3/include/bits/chrono_io.h
> index 620227a9f35..ace8b9f2629 100644
> --- a/libstdc++-v3/include/bits/chrono_io.h
> +++ b/libstdc++-v3/include/bits/chrono_io.h
> @@ -503,9 +503,7 @@ namespace __format
> _M_format(const _Tp& __t, _FormatContext& __fc,
> bool __is_neg = false) const
> {
> - auto __first = _M_spec._M_chrono_specs.begin();
> - const auto __last = _M_spec._M_chrono_specs.end();
> - if (__first == __last)
> + if (_M_spec._M_chrono_specs.empty())
> return _M_format_to_ostream(__t, __fc, __is_neg);
>
> #if defined _GLIBCXX_USE_NL_LANGINFO_L && __CHAR_BIT__ == 8
> @@ -525,29 +523,29 @@ namespace __format
> __fc._M_loc = __with_encoding_conversion(__loc);
> }
> #endif
> -
> - _Sink_iter<_CharT> __out;
> - __format::_Str_sink<_CharT> __sink;
> - bool __write_direct = false;
> - if constexpr (is_same_v<typename _FormatContext::iterator,
> - _Sink_iter<_CharT>>)
> - {
> - if (_M_spec._M_width_kind == __format::_WP_none)
> - {
> - __out = __fc.out();
> - __write_direct = true;
> - }
> - else
> - __out = __sink.out();
> - }
> - else
> - __out = __sink.out();
> -
> // formatter<duration> passes the correct value of __is_neg
> // for durations but for hh_mm_ss we decide it here.
> if constexpr (__is_specialization_of<_Tp, chrono::hh_mm_ss>)
> __is_neg = __t.is_negative();
>
> + const size_t __padwidth = _M_spec._M_get_width(__fc);
> + if (__padwidth == 0)
> + return _M_format_to(__t, __fc.out(), __fc, __is_neg);
> +
> + using _Out = typename _FormatContext::iterator;
> + _Padding_sink<_Out, _CharT> __sink(__fc.out(), __padwidth);
> + _M_format_to(__t, __sink.out(), __fc, __is_neg);
> + return __sink._M_finish(_M_spec._M_align, _M_spec._M_fill);
> + }
> +
> + template<typename _Tp, typename _Out, typename _FormatContext>
> + _Out
> + _M_format_to(const _Tp& __t, _Out __out, _FormatContext& __fc,
> + bool __is_neg) const
> + {
> + auto __first = _M_spec._M_chrono_specs.begin();
> + const auto __last = _M_spec._M_chrono_specs.end();
> +
> auto __print_sign = [&__is_neg, &__out] {
> if constexpr (chrono::__is_duration_v<_Tp>
> || __is_specialization_of<_Tp,
> chrono::hh_mm_ss>)
> @@ -699,20 +697,7 @@ namespace __format
> }
> }
> while (__first != __last);
> -
> - if constexpr (is_same_v<typename _FormatContext::iterator,
> - _Sink_iter<_CharT>>)
> - if (__write_direct)
> - return __out;
> -
> - auto __str = __sink.view();
> - size_t __width;
> - if constexpr (__unicode::__literal_encoding_is_unicode<_CharT>())
> - __width = __unicode::__field_width(__str);
> - else
> - __width = __str.size();
> - return __format::__write_padded_as_spec(__str, __width,
> - __fc, _M_spec);
> + return std::move(__out);
> }
>
> _ChronoSpec<_CharT> _M_spec;
> --
> 2.49.0
>
>
