From owner-cvs-all@FreeBSD.ORG Thu Feb 7 09:42:19 2008 Return-Path: Delivered-To: cvs-all@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E6C6E16A421; Thu, 7 Feb 2008 09:42:19 +0000 (UTC) (envelope-from bde@FreeBSD.org) Received: from repoman.freebsd.org (repoman.freebsd.org [IPv6:2001:4f8:fff6::29]) by mx1.freebsd.org (Postfix) with ESMTP id C584F13C4DB; Thu, 7 Feb 2008 09:42:19 +0000 (UTC) (envelope-from bde@FreeBSD.org) Received: from repoman.freebsd.org (localhost [127.0.0.1]) by repoman.freebsd.org (8.14.1/8.14.1) with ESMTP id m179gJWd044006; Thu, 7 Feb 2008 09:42:19 GMT (envelope-from bde@repoman.freebsd.org) Received: (from bde@localhost) by repoman.freebsd.org (8.14.1/8.14.1/Submit) id m179gJjO044005; Thu, 7 Feb 2008 09:42:19 GMT (envelope-from bde) Message-Id: <200802070942.m179gJjO044005@repoman.freebsd.org> From: Bruce Evans Date: Thu, 7 Feb 2008 09:42:19 +0000 (UTC) To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org X-FreeBSD-CVS-Branch: HEAD Cc: Subject: cvs commit: src/lib/msun/src s_expm1.c s_expm1f.c X-BeenThere: cvs-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the entire tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 07 Feb 2008 09:42:20 -0000 bde 2008-02-07 09:42:19 UTC FreeBSD src repository Modified files: lib/msun/src s_expm1.c s_expm1f.c Log: Use a better method of scaling by 2**k. Instead of adding to the exponent bits of the reduced result, construct 2**k (hopefully in parallel with the construction of the reduced result) and multiply by it. This tends to be much faster if the construction of 2**k is actually in parallel, and might be faster even with no parallelism since adjustment of the exponent requires a read-modify-wrtite at an unfortunate time for pipelines. In some cases involving exp2* on amd64 (A64), this change saves about 40 cycles or 30%. I think it is inherently only about 12 cycles faster in these cases and the rest of the speedup is from partly-accidentally avoiding compiler pessimizations (the construction of 2**k is now manually scheduled for good results, and -O2 doesn't always mess this up). In most cases on amd64 (A64) and i386 (A64) the speedup is about 20 cycles. The worst case that I found is expf on ia64 where this change is a pessimization of about 10 cycles or 5%. The manual scheduling for plain exp[f] is harder and not as tuned. Details specific to expm1*: - the saving is closer to 12 cycles than to 40 for expm1* on i386 (A64). For some reason it is much larger for negative args. - also convert to __FBSDID(). Revision Changes Path 1.8 +8 -13 src/lib/msun/src/s_expm1.c 1.8 +8 -13 src/lib/msun/src/s_expm1f.c