From patchwork Wed Nov 16 21:00:14 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jonathan Wakely X-Patchwork-Id: 60719 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 592243973112 for ; Wed, 16 Nov 2022 21:01:59 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 592243973112 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1668632519; bh=A6HteluHMJQ24IH53RB4mTZY8ZW8xu/MEzOkvDttZbY=; h=To:Subject:Date:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:From; b=INRKgMk903bKBAzPuiTnKXhXA8sDMGEcTnLeLqhaR4YzZpoWDTP0PLAIQkR0N1RkS 5IF7Awsa0A8U25zfHW11dpPvxZhXHBJovAWUCguqLpyetl8vc6YcmC9xgXvxc0TFon Xpw1cf+7di+GcUJMYfYjfTsJ156U03g4gDnpYU0g= X-Original-To: gcc-patches@gcc.gnu.org Delivered-To: gcc-patches@gcc.gnu.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 2A354396E463 for ; Wed, 16 Nov 2022 21:00:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 2A354396E463 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-529-FDpR2rAnOGuOQ4SUdSxL8w-1; Wed, 16 Nov 2022 16:00:17 -0500 X-MC-Unique: FDpR2rAnOGuOQ4SUdSxL8w-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4C4251C08975; Wed, 16 Nov 2022 21:00:17 +0000 (UTC) Received: from localhost (unknown [10.33.36.199]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1601F49BB60; Wed, 16 Nov 2022 21:00:16 +0000 (UTC) To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [committed] libstdc++: Improve performance of chrono::utc_clock::now() Date: Wed, 16 Nov 2022 21:00:14 +0000 Message-Id: <20221116210014.1420128-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-12.2 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Jonathan Wakely via Gcc-patches From: Jonathan Wakely Reply-To: Jonathan Wakely Errors-To: gcc-patches-bounces+patchwork=sourceware.org@gcc.gnu.org Sender: "Gcc-patches" Tested x86_64-linux. Pushed to trunk. -- >8 -- We can use an array instead of a std::vector, and we can avoid the binary search for the common case of a time point after the most recent leap second. On one system where I tested this, utc_clock::now() now takes about 16ns instead of 31ns. libstdc++-v3/ChangeLog: * include/std/chrono (get_leap_second_info): Optimize. --- libstdc++-v3/include/std/chrono | 31 ++++++++++++++++++++++++------- 1 file changed, 24 insertions(+), 7 deletions(-) diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono index 90b73f8198e..2468023f6c5 100644 --- a/libstdc++-v3/include/std/chrono +++ b/libstdc++-v3/include/std/chrono @@ -2747,9 +2747,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { if constexpr (is_same_v<_Duration, seconds>) { - // TODO move this function into the library and get leaps from tzdb. - vector __leaps - { + const seconds::rep __leaps[] { 78796800, // 1 Jul 1972 94694400, // 1 Jan 1973 126230400, // 1 Jan 1974 @@ -2778,12 +2776,31 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION 1435708800, // 1 Jul 2015 1483228800, // 1 Jan 2017 }; + // The list above is known to be valid until 2023-06-28 00:00:00 UTC + const seconds::rep __expires = 1687910400; + const seconds::rep __s = __ut.time_since_epoch().count(); - auto __s = __ut.time_since_epoch().count(); - auto __pos = std::upper_bound(__leaps.begin(), __leaps.end(), __s); + const seconds::rep* __first = std::begin(__leaps); + const seconds::rep* __last = std::end(__leaps); + + if (__s > __expires) + { + // TODO: use updated leap_seconds from tzdb +#if 0 + auto __db = get_tzdb_list().begin(); + __first = __db->leap_seconds.data(); + __last = __first + __db->leap_seconds.size(); +#endif + } + + // Don't bother searching the list if we're after the last one. + if (__s > __last[-1]) + return { false, seconds(__last - __first) }; + + auto __pos = std::upper_bound(__first, __last, __s); return { - __pos != __leaps.begin() && __pos[-1] == __s, - seconds{__pos - __leaps.begin()} + __pos != begin(__leaps) && __pos[-1] == __s, + seconds{__pos - __first} }; } else