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 [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id C108F3858D33 for ; Thu, 9 Mar 2023 08:05:44 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org C108F3858D33 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678349144; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=v0WmJSXAOX3b/bMbkYxHKQhcZyHWxc67q7Fwe/jFufY=; b=TTzzL1e0u14pxnj5+dFiQm6lxpsYuxvpNcMv5rJMyslGnNmclnjtkXxnsN2vwjj9dW9dHL P1jXWgpz60aYZ8Srf5pNoRO5LPbHKdiONphsNZmrIJO0JUwELMxsMZi2PU8PEAlQLRJC3V oYupR7FajNyKasBh4S5CQy7cV0BMO2o= 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-460-JLjSGnnYPJ2I9G9C6HihlQ-1; Thu, 09 Mar 2023 03:05:43 -0500 X-MC-Unique: JLjSGnnYPJ2I9G9C6HihlQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A628A80D0E3; Thu, 9 Mar 2023 08:05:42 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 68BDB492C3E; Thu, 9 Mar 2023 08:05:42 +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 32985dAU695528 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Thu, 9 Mar 2023 09:05:39 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 32985b2F695527; Thu, 9 Mar 2023 09:05:37 +0100 Date: Thu, 9 Mar 2023 09:05:37 +0100 From: Jakub Jelinek To: Gerald Pfeifer Cc: Martin =?utf-8?B?TGnFoWth?= , gcc-patches@gcc.gnu.org Subject: Re: [wwwdocs] gcc-13/porting_to.html: Document C++ -fexcess-precision=standard Message-ID: Reply-To: Jakub Jelinek References: <541d2859-4029-3a21-e57e-10a401c5d226@pfeifer.com> <1a4e7d15-0bb8-d083-e168-0a9cc6b38584@pfeifer.com> MIME-Version: 1.0 In-Reply-To: <1a4e7d15-0bb8-d083-e168-0a9cc6b38584@pfeifer.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 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=-9.4 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 List-Id: On Thu, Mar 09, 2023 at 08:09:02AM +0100, Gerald Pfeifer wrote: > I struggled a bit understanding this and so have come up with what I > hope is simpler (without changing the meaning). > > What do you think of the change below? LGTM, thanks. > > diff --git a/htdocs/gcc-13/porting_to.html b/htdocs/gcc-13/porting_to.html > index 170da096..8a2822ff 100644 > --- a/htdocs/gcc-13/porting_to.html > +++ b/htdocs/gcc-13/porting_to.html > @@ -122,12 +122,14 @@ the operand as an lvalue.
> >

Excess precision changes

> > -

GCC 13 implements in C++ excess precision support > -which has been before implemented just in the C front end. The new behavior is > -enabled by default in -std=c++NN modes and e.g. when > -FLT_EVAL_METHOD is 1 or 2 affects behavior of floating point > -constants and expressions. E.g. for FLT_EVAL_METHOD equal > -to 2 on ia32: > +

GCC 13 implements excess precision > +support, which was implemented just in the C front end > +before, in C++. The new behavior is enabled by default in > +-std=c++NN modes and when > +FLT_EVAL_METHOD is 1 or 2 and affects the behavior of > +floating point constants and expressions.

> + > +

E.g. for FLT_EVAL_METHOD equal to 2 on ia32 > > 


>  #include <stdlib.h>
> @@ -139,11 +141,11 @@ will not abort with standard excess precision, because constants and expressions
>  in float or double are evaluated in precision of
>  long double and demoted only on casts or assignments, but will
>  abort with fast excess precision, where whether something is evaluated in
> -precision of long double or not depends on what evaluations are
> -done in the i387 floating point stack or are spilled from it.
> +long double precision depends on what evaluations are
> +done in the i387 floating point stack or are spilled from it.

>  
> -The -fexcess-precision=fast option can be used to request the
> -previous behavior.
> +
The -fexcess-precision=fast option can be used to
> +request the previous behavior.

>  
>  
allocator_traits<A>::rebind_alloc<A::value_type> must be A

>  

	Jakub