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In case readers are misled by expressions that combine multiplication and

Browse source 
division, add parentheses to make the precedence explicit.

Submitted by:	Doug Moore <dougm@rice.edu>
Requested by:	imp
Reviewed by:	imp
MFC after:	1 week
X-MFC after:	r321840
Differential Revision:	https://reviews.freebsd.org/D11815
This commit is contained in:
Alan Cox 2017-08-04 04:23:23 +00:00
parent f48bfebce1
commit ba98e6a2d7
1 changed files with 10 additions and 5 deletions
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15
sys/kern/subr_blist.c
View file

@ -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 blk, daddr_t radix,
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)));
}
/*