From 8ae50799cd25a63fa028eb6aad4f93be1d8eeb39 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 14 Dec 2023 15:29:13 +0000
Subject: [PATCH] libstdc++: Simplify some chrono formatters
I don't remember exactly why I made these bits of code reserve space in
a COW string and append to it, rather than just use the string returned
from std::format (which will undergo copy elision). The _Str_sink type
used by std::format means the string only performs a single allocation
for the formatted output, and the returned string's reference count will
be one, so won't reallocate when indexing into it. We can remove these
non-optimizations.
libstdc++-v3/ChangeLog:
* include/bits/chrono_io.h (__formatter_chrono::_M_F): Simplify
handling of string returned from std::format.
(__formatter_chrono::_M_R_T): Likewise.
---
libstdc++-v3/include/bits/chrono_io.h | 14 ++++----------
1 file changed, 4 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index ec2ae9d53cc2..7b5876b24e6b 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -898,11 +898,8 @@ namespace __format
_FormatContext&) const
{
auto __ymd = _S_date(__t);
- basic_string<_CharT> __s;
-#if ! _GLIBCXX_USE_CXX11_ABI
- __s.reserve(11);
-#endif
- __s += std::format(_GLIBCXX_WIDEN("{:04d}- - "), (int)__ymd.year());
+ auto __s = std::format(_GLIBCXX_WIDEN("{:04d}- - "),
+ (int)__ymd.year());
auto __sv = _S_two_digits((unsigned)__ymd.month());
__s[__s.size() - 5] = __sv[0];
__s[__s.size() - 4] = __sv[1];
@@ -1093,11 +1090,8 @@ namespace __format
// %T Equivalent to %H:%M:%S
auto __hms = _S_hms(__t);
- basic_string<_CharT> __s;
-#if ! _GLIBCXX_USE_CXX11_ABI
- __s.reserve(11);
-#endif
- __s = std::format(_GLIBCXX_WIDEN("{:02d}:00"), __hms.hours().count());
+ auto __s = std::format(_GLIBCXX_WIDEN("{:02d}:00"),
+ __hms.hours().count());
auto __sv = _S_two_digits(__hms.minutes().count());
__s[__s.size() - 2] = __sv[0];
__s[__s.size() - 1] = __sv[1];
--
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