From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: [committed] libstdc++: Use unsigned division in std::rotate [PR113811]
Date: Thu, 15 Feb 2024 11:46:16 +0000 [thread overview]
Message-ID: <20240215114628.50110-1-jwakely@redhat.com> (raw)
Tested aarch64-linux and x86_64-linux. Pushed to trunk.
-- >8 --
Signed 64-bit division is much slower than unsigned, so cast the n and
k values to unsigned before doing n %= k. We know this is safe because
neither value can be negative.
libstdc++-v3/ChangeLog:
PR libstdc++/113811
* include/bits/stl_algo.h (__rotate): Use unsigned values for
division.
---
libstdc++-v3/include/bits/stl_algo.h | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 9496b53f887..7a0cf6b6737 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -1251,6 +1251,12 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
typedef typename iterator_traits<_RandomAccessIterator>::value_type
_ValueType;
+#if __cplusplus >= 201103L
+ typedef typename make_unsigned<_Distance>::type _UDistance;
+#else
+ typedef _Distance _UDistance;
+#endif
+
_Distance __n = __last - __first;
_Distance __k = __middle - __first;
@@ -1281,7 +1287,7 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
++__p;
++__q;
}
- __n %= __k;
+ __n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
if (__n == 0)
return __ret;
std::swap(__n, __k);
@@ -1305,7 +1311,7 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
--__q;
std::iter_swap(__p, __q);
}
- __n %= __k;
+ __n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
if (__n == 0)
return __ret;
std::swap(__n, __k);
--
2.43.0
reply other threads:[~2024-02-15 11:46 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20240215114628.50110-1-jwakely@redhat.com \
--to=jwakely@redhat.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=libstdc++@gcc.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).