Messages in this thread | | | Date | Sun, 29 Mar 2020 04:00:12 +0000 | From | George Spelvin <> | Subject | Re: [RFC PATCH v1 08/50] fs/ext4/ialloc.c: Replace % with reciprocal_scale() TO BE VERIFIED |
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On Sat, Mar 28, 2020 at 06:10:11PM -0600, Andreas Dilger wrote: > On Mar 28, 2020, at 5:15 PM, George Spelvin <lkml@SDF.ORG> wrote: >> Also, we could, if desired, eliminate the i variable entirely >> using the fact that we have a copy of the starting position cached >> in parent_group. I.e. >> >> g = parent_group = reciprocal_scale(grp, ngroups); >> - for (i = 0; i < ngroups; i++, ++g == ngroups && (g = 0)) { >> + do { >> ... >> - } >> + if (++g == ngroups) >> + g = 0; >> + } while (g != parent_group);
> I was looking at whether we could use a for-loop without "i"? Something like: > > for (g = parent_group + 1; g != parent_group; ++g >= ngroups && (g = 0)) > > The initial group is parent_group + 1, to avoid special-casing when the > initial parent_group = 0 (which would prevent the loop from terminating).
That's the first option I presented, above. Since a for() loop tests before each iteration, if the counter is strictly modulo ngroups, there's no way to execute the loop body more than ngroups-1 times.
That's why I changed to do{}while(), which has a minimum of 1 (it can't handle ngroups == 0), but can mimic the current loop's execution perfectly (no initial +1 offset).
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