Date: Fri, 4 Aug 2017 10:25:49 -0500 From: Alan Cox <alc@rice.edu> To: Oliver Pinter <oliver.pinter@hardenedbsd.org>, Alan Cox <alc@freebsd.org> Cc: "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r322041 - head/sys/kern Message-ID: <773de469-dc2f-d335-2506-bdf0a4db848a@rice.edu> In-Reply-To: <CAPQ4ffu7ZG9EsQyhHJF%2BESLAn32VXFZ43qya05D2R-zrsMuu=A@mail.gmail.com> References: <201708040423.v744NOix022999@repo.freebsd.org> <CAPQ4ffu7ZG9EsQyhHJF%2BESLAn32VXFZ43qya05D2R-zrsMuu=A@mail.gmail.com>
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On 08/04/2017 02:57, Oliver Pinter wrote: > > > On Friday, August 4, 2017, Alan Cox <alc@freebsd.org > <mailto:alc@freebsd.org>> wrote: > > Author: alc > Date: Fri Aug 4 04:23:23 2017 > New Revision: 322041 > URL: https://svnweb.freebsd.org/changeset/base/322041 > <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 <dougm@rice.edu <javascript:;>> > Requested by: imp > Reviewed by: imp > MFC after: 1 week > X-MFC after: r321840 > Differential Revision: https://reviews.freebsd.org/D11815 > <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) > > > Is this dummy define intended? > Yes, it is for user-space, stand-alone compilation of this file. > > #include <sys/blist.h> > > @@ -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))); > } > > /* > _______________________________________________ > svn-src-head@freebsd.org <javascript:;> mailing list > https://lists.freebsd.org/mailman/listinfo/svn-src-head > <https://lists.freebsd.org/mailman/listinfo/svn-src-head>; > To unsubscribe, send any mail to > "svn-src-head-unsubscribe@freebsd.org <javascript:;>" >
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