From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 AE2D93858D28 for ; Fri, 1 Jul 2022 16:58:53 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org AE2D93858D28 Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-547-VMGjliM-NQm8V2-uTx_6jw-1; Fri, 01 Jul 2022 12:58:50 -0400 X-MC-Unique: VMGjliM-NQm8V2-uTx_6jw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0DFAC101A589; Fri, 1 Jul 2022 16:58:50 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.30]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BC1501121314; Fri, 1 Jul 2022 16:58:49 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 261GwlXn1652442 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Fri, 1 Jul 2022 18:58:47 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 261GwkJq1652441; Fri, 1 Jul 2022 18:58:46 +0200 Date: Fri, 1 Jul 2022 18:58:46 +0200 From: Jakub Jelinek To: Aldy Hernandez Cc: GCC patches , Andrew MacLeod , Richard Sandiford Subject: Re: [RFC] trailing_wide_ints with runtime variable lengths Message-ID: Reply-To: Jakub Jelinek References: <20220629092157.230287-1-aldyh@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-4.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE 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-List-Received-Date: Fri, 01 Jul 2022 16:58:55 -0000 On Fri, Jul 01, 2022 at 06:47:48PM +0200, Aldy Hernandez wrote: > > So, you are looking for something like trailing_wide_ints but where that > > N is actually a runtime value? Then e.g. the > > struct {unsigned char len;} m_len[N]; > > member can't work properly either, because it isn't constant size. > > What my patch does is store the run-time length in the aforementioned > byte, while defaulting to N/MAX. There is no size difference (or code > changes) for existing users. With my change, set_precision() and > extra_size() now take a runtime parameter, but it defaults to N and is > inlined, so there is no penalty for existing users. I benchmarked to > make sure :). So, you still use N = 3 but can sometimes store say 255 wide_ints in there? In that case, m_len[N] provides lengths just for the first 3, no? Anyway, you really want feedback from Richard Sandiford IMHO... Jakub