From owner-svn-src-all@freebsd.org Fri Aug 4 04:23:25 2017 Return-Path: Delivered-To: svn-src-all@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 1E321DC4ACD; Fri, 4 Aug 2017 04:23:25 +0000 (UTC) (envelope-from alc@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id DE2937D0D5; Fri, 4 Aug 2017 04:23:24 +0000 (UTC) (envelope-from alc@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id v744NOn8023000; Fri, 4 Aug 2017 04:23:24 GMT (envelope-from alc@FreeBSD.org) Received: (from alc@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id v744NOix022999; Fri, 4 Aug 2017 04:23:24 GMT (envelope-from alc@FreeBSD.org) Message-Id: <201708040423.v744NOix022999@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: alc set sender to alc@FreeBSD.org using -f From: Alan Cox Date: Fri, 4 Aug 2017 04:23:24 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r322041 - head/sys/kern X-SVN-Group: head X-SVN-Commit-Author: alc X-SVN-Commit-Paths: head/sys/kern X-SVN-Commit-Revision: 322041 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 04 Aug 2017 04:23:25 -0000 Author: alc Date: Fri Aug 4 04:23:23 2017 New Revision: 322041 URL: https://svnweb.freebsd.org/changeset/base/322041 Log: In case readers are misled by expressions that combine multiplication and division, add parentheses to make the precedence explicit. Submitted by: Doug Moore Requested by: imp Reviewed by: imp MFC after: 1 week X-MFC after: r321840 Differential Revision: https://reviews.freebsd.org/D11815 Modified: head/sys/kern/subr_blist.c Modified: head/sys/kern/subr_blist.c ============================================================================== --- head/sys/kern/subr_blist.c Fri Aug 4 04:20:11 2017 (r322040) +++ head/sys/kern/subr_blist.c Fri Aug 4 04:23:23 2017 (r322041) @@ -110,6 +110,7 @@ __FBSDID("$FreeBSD$"); #define bitcount64(x) __bitcount64((uint64_t)(x)) #define malloc(a,b,c) calloc(a, 1) #define free(a,b) free(a) +#define CTASSERT(expr) #include @@ -142,6 +143,8 @@ static void blst_radix_print(blmeta_t *scan, daddr_t b static MALLOC_DEFINE(M_SWAP, "SWAP", "Swap space"); #endif +CTASSERT(BLIST_BMAP_RADIX % BLIST_META_RADIX == 0); + /* * For a subtree that can represent the state of up to 'radix' blocks, the * number of leaf nodes of the subtree is L=radix/BLIST_BMAP_RADIX. If 'm' @@ -151,17 +154,19 @@ static MALLOC_DEFINE(M_SWAP, "SWAP", "Swap space"); * in the 'meta' functions that process subtrees. Since integer division * discards remainders, we can express this computation as * skip = (m * m**h) / (m - 1) - * skip = (m * radix / BLIST_BMAP_RADIX) / (m - 1) - * and if m divides BLIST_BMAP_RADIX, we can simplify further to - * skip = radix / (BLIST_BMAP_RADIX / m * (m - 1)) - * so that a simple integer division is enough for the calculation. + * skip = (m * (radix / BLIST_BMAP_RADIX)) / (m - 1) + * and since m divides BLIST_BMAP_RADIX, we can simplify further to + * skip = (radix / (BLIST_BMAP_RADIX / m)) / (m - 1) + * skip = radix / ((BLIST_BMAP_RADIX / m) * (m - 1)) + * so that simple integer division by a constant can safely be used for the + * calculation. */ static inline daddr_t radix_to_skip(daddr_t radix) { return (radix / - (BLIST_BMAP_RADIX / BLIST_META_RADIX * (BLIST_META_RADIX - 1))); + ((BLIST_BMAP_RADIX / BLIST_META_RADIX) * (BLIST_META_RADIX - 1))); } /*