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 <do...@rice.edu> 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 <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-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
