Messages in this thread |  | | Date | Sun, 21 Jan 2024 11:17:30 -0500 | | From | Kent Overstreet <> | | Subject | Re: [PATCH 2/5] bcachefs: Introduce parent function for sort_cmp_size() |
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On Sun, Jan 21, 2024 at 11:36:46PM +0800, Kuan-Wei Chiu wrote: > When dealing with array indices, the parent's index can be obtained > using the formula (i - 1) / 2. However, when working with byte offsets, > this approach is not straightforward. To address this, we have > introduced a branch-free parent function that does not require any > division operations to calculate the parent's byte offset.
This is a good commit message - but it would be even better if it was a function comment on parent()
> > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com> > --- > This patch has undergone unit testing using the following code [1]. > > [1]: > static int test(void) > { > size_t i, p, size, lsbit; > > for (i = 0; i < 10000; i++) { > size = get_random_u32() % (1U << 10); > lsbit = size & -size; > i = get_random_u32() % (1U << 20) * size + size; > p = parent(i, lsbit, size); > if (p != (i / size - 1) / 2 * size) > return -1; > } > > return 0; > } > > fs/bcachefs/util.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/fs/bcachefs/util.c b/fs/bcachefs/util.c > index bbc83b43162e..f5bbf96df2ce 100644 > --- a/fs/bcachefs/util.c > +++ b/fs/bcachefs/util.c > @@ -907,6 +907,13 @@ static inline void do_swap(void *base, size_t n, size_t size, > size); > } > > +static inline size_t parent(size_t i, size_t lsbit, size_t size) > +{ > + i -= size; > + i -= size & -(i & lsbit); > + return i >> 1; > +} > + > void eytzinger0_sort(void *base, size_t n, size_t size, > int (*cmp_func)(const void *, const void *, size_t), > void (*swap_func)(void *, void *, size_t)) > -- > 2.25.1 >
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