From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 16785 invoked by alias); 17 Dec 2001 21:10:27 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 16748 invoked from network); 17 Dec 2001 21:10:25 -0000 Received: from unknown (HELO igw3.watson.ibm.com) (198.81.209.18) by sources.redhat.com with SMTP; 17 Dec 2001 21:10:25 -0000 Received: from sp1n293en1.watson.ibm.com (sp1n293en1.watson.ibm.com [9.2.112.57]) by igw3.watson.ibm.com (8.11.4/8.11.4) with ESMTP id fBHL9rn11784; Mon, 17 Dec 2001 16:09:53 -0500 Received: from makai.watson.ibm.com (makai.watson.ibm.com [9.2.216.144]) by sp1n293en1.watson.ibm.com (8.11.4/8.11.4) with ESMTP id fBHL9rn29828; Mon, 17 Dec 2001 16:09:53 -0500 Received: from watson.ibm.com (localhost [127.0.0.1]) by makai.watson.ibm.com (AIX4.3/8.9.3/8.9.3/01-10-2000) with ESMTP id QAA22442; Mon, 17 Dec 2001 16:09:53 -0500 Message-Id: <200112172109.QAA22442@makai.watson.ibm.com> To: degger@fhm.edu cc: gcc-patches@gcc.gnu.org, gcc@gcc.gnu.org Subject: Re: Patch to add missing PPC instruction In-Reply-To: Message from degger@fhm.edu of "Mon, 17 Dec 2001 20:02:56 +0100." <20011217200939.8F8296EE2@Nicole.fhm.edu> Date: Mon, 17 Dec 2001 13:11:00 -0000 From: David Edelsohn X-SW-Source: 2001-12/txt/msg00934.txt.bz2 >>>>> degger writes: degger> the attached patch is supposed to add the the fres instruction degger> and necessary computation code to the rs6000 backend. degger> fres is a "floating point single precision reciprocal" mnemonic degger> which is available on at least the 7400 and 7410 (haven't heard degger> back from Dale which other CPUs have it, but they can be added later) degger> which is faster than a single precision divide and spares the storage degger> for the 1.0, a register and the necessary load instructions to get them degger> into memory. degger> This has boostrapped on powerpc-linux-gnu and passed the testsuite degger> without regressions. fres is floating-point reciprocal ESTIMATE Single, not a single-precision reciprocal. It is accurate to one part in either 256 or 4096, not IEEE 754 Single Precision accuracy. It is part of the PowerPC optional instructions for graphics. The instruction is meant as an estimate starting point for a Newton-Raphson approximation algorithm. It does not do what you are assuming and this patch is rejected. David