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Replace the expression "-mask & ~mask" with a function call that does

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the same thing, but is commented so that it might be better
understood.

Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20231
This commit is contained in:
Doug Moore 2019-05-10 19:55:29 +00:00
parent f04019c3c6
commit 09b380a1ff
1 changed files with 14 additions and 1 deletions
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15
sys/kern/subr_blist.c
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@ -642,6 +642,19 @@ blst_next_leaf_alloc(blmeta_t *scan, daddr_t blk, int count)
return (0);
}
/*
* Given a bitmask, flip all the bits from the least-significant 1-bit to the
* most significant bit. If the result is non-zero, then the least-significant
* 1-bit of the result is in the same position as the least-signification 0-bit
* in mask that is followed by a 1-bit.
*/
static inline u_daddr_t
flip_hibits(u_daddr_t mask)
{
return (-mask & ~mask);
}
/*
* BLST_LEAF_ALLOC() - allocate at a leaf in the radix tree (a bitmap).
*
@ -659,7 +672,7 @@ blst_leaf_alloc(blmeta_t *scan, daddr_t blk, int count)
count1 = count - 1;
num_shifts = fls(count1);
mask = scan->bm_bitmap;
while ((-mask & ~mask) != 0 && num_shifts > 0) {
while (flip_hibits(mask) != 0 && num_shifts > 0) {
/*
* If bit i is set in mask, then bits in [i, i+range1] are set
* in scan->bm_bitmap. The value of range1 is equal to count1