From owner-svn-src-head@freebsd.org Sun May 29 21:16:59 2016 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id D48CAB53429 for ; Sun, 29 May 2016 21:16:59 +0000 (UTC) (envelope-from mailing-machine@vniz.net) Received: from mail-lf0-f49.google.com (mail-lf0-f49.google.com [209.85.215.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 688AC1D47 for ; Sun, 29 May 2016 21:16:59 +0000 (UTC) (envelope-from mailing-machine@vniz.net) Received: by mail-lf0-f49.google.com with SMTP id k98so65128826lfi.1 for ; Sun, 29 May 2016 14:16:59 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:cc:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=sbsTSmb8qNT4t6K63om8E39+nWgDeIi1SPXLSdwDNGI=; b=jOLuAyjp1n9wlcQeRf/nNj+ELQvUK1N1beBBPqIUBGGvahY4NP9ql7VRyBJpkYQ2FH dEUinHBkWBwZeVEARCw+oGzj4glMDNKv2nzw8L6xonYgAEMuy0M5fiN39xvEegy0g6Ig PP9Q7FNi7s59Ep8AZ+jrrBIkPTuVhr2lr+1kLUl7ADD9iaGCqRWpOufPzx1NMT/L92c8 WUQtXXGYsvJfIeZKBXipDcRHT0RDKlpbE1GX19R67xRPg+a04zylt13ViL7Rh/OlIv+K 0zdElJa7t+8ZtU0HoIfgdnwvk0XXfeNs38gtZPnm1WBhAPccnO+PpQA3qdgDF5w1FUtf MugQ== X-Gm-Message-State: ALyK8tL1QPpkqDmjrZc41UQWp65sa2M05v7B7duqKcWSm4cUzB17CPDhKiXafpSqGNa0AA== X-Received: by 10.25.40.144 with SMTP id o138mr6289295lfo.160.1464553256117; Sun, 29 May 2016 13:20:56 -0700 (PDT) Received: from [192.168.1.2] ([89.169.173.68]) by smtp.gmail.com with ESMTPSA id u202sm1712654lja.12.2016.05.29.13.20.55 (version=TLSv1/SSLv3 cipher=OTHER); Sun, 29 May 2016 13:20:55 -0700 (PDT) Subject: Re: svn commit: r300965 - head/lib/libc/stdlib To: cem@FreeBSD.org References: <201605291639.u4TGdSwq032144@repo.freebsd.org> Cc: src-committers , svn-src-all@freebsd.org, svn-src-head@freebsd.org From: Andrey Chernov Message-ID: Date: Sun, 29 May 2016 23:20:54 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 29 May 2016 21:16:59 -0000 On 29.05.2016 22:39, Conrad Meyer wrote: > Does clang actually generate different code with this change? Yes, without -O it generates andl $2147483647, ... With -O nothing is changed. In general, it can be not clang and I see no point to left junk code in any case. > > On Sun, May 29, 2016 at 9:39 AM, Andrey A. Chernov wrote: >> Author: ache >> Date: Sun May 29 16:39:28 2016 >> New Revision: 300965 >> URL: https://svnweb.freebsd.org/changeset/base/300965 >> >> Log: >> Micro optimize: C standard guarantees that right shift for unsigned value >> fills left bits with zero, and we have exact 32bit unsigned value >> (uint32_t), so there is no reason to add "& 0x7fffffff" here. >> >> MFC after: 1 week >> >> Modified: >> head/lib/libc/stdlib/random.c >> >> Modified: head/lib/libc/stdlib/random.c >> ============================================================================== >> --- head/lib/libc/stdlib/random.c Sun May 29 16:32:56 2016 (r300964) >> +++ head/lib/libc/stdlib/random.c Sun May 29 16:39:28 2016 (r300965) >> @@ -430,7 +430,7 @@ random(void) >> */ >> f = fptr; r = rptr; >> *f += *r; >> - i = (*f >> 1) & 0x7fffffff; /* chucking least random bit */ >> + i = *f >> 1; /* chucking least random bit */ >> if (++f >= end_ptr) { >> f = state; >> ++r; >> >