Re: [PATCH v2] lib/string_helpers: renormalize string_get_size() after rounding carry

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2026-04-21 at 07:53 +0300, Andy Shevchenko wrote:
> On Tue, Apr 21, 2026 at 6:38 AM Shuvam Pandey
> <shuvampandey1@gmail.com> wrote:
> 
> > > Well firstly I would note that the original behaviour isn't a
> > > bug.
> 
> James, thank you for the prompt reply!
> 
> > So I agree this should not go forward as a bug fix in its current
> > form. I'll drop this patch here and revisit it only if I can come
> > back with a better understanding of the intended semantics.
> 
> Shuvam, perhaps we need to add a few more test cases first to
> understand current behaviour better?

Sure, but the base 2 one is the problem.  It will go up to 1023 in
whatever units but for binary that's under 1 of the next unit up.  So

1023 B == 1.00 KiB
1018 B == 0.99 KiB
1000 B == 0.98 KiB

And so on.  However, technically the latter two (when converted to the
upper unit) are only 2sf not 3 because the leading zero doesn't count.
If you run the above to 3sf it comes out

1023 B == 0.999 KiB
1018 B == 0.994 KiB
1000 B == 0.977 KiB

If the desire is really to be 3sf everywhere, you need the latter and
the routine can be adjusted to do that: the while  around the do_div
would have to be checking strictly >= 1000 and you now have to set j=0
if size comes out 0.  Rounding also has to be done inside that loop now
(because too much precision is lost in the j = 3 case).

But, like I said, this isn't a bug fix it's a behaviour change.

Regards,

James