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

[Andy Shevchenko <andy.shevchenko@gmail.com>]

Please, keep the author of the original change in the loop.

James, what do you think?

On Sun, Apr 19, 2026 at 6:31 PM Shuvam Pandey <shuvampandey1@gmail.com> wrote:
>
> string_get_size() rounds the fractional part before formatting the
> result. If that carry pushes the integer part to the unit divisor, the
> helper still prints the old unit and produces strings like "1000 kB"
> and "1024 KiB".
>
> That misformatted carry case comes from the arithmetic rounding added by
> commit 564b026fbd0d ("string_helpers: fix precision loss for some
> inputs"). The helper already rounds those values up numerically; it
> just fails to renormalize them into the next unit before formatting.
>
> Renormalize the carried result into the next named unit so those cases
> print as "1.00 MB" and "1.00 MiB" instead. Only do that when another
> named unit exists, so the existing "UNK" fallback is preserved at the
> top end. Extend the KUnit coverage around the first decimal and binary
> boundaries, including adjacent values and non-byte block sizes that hit
> the same carry path.
>
> Fixes: 564b026fbd0d ("string_helpers: fix precision loss for some inputs")
> Signed-off-by: Shuvam Pandey <shuvampandey1@gmail.com>
> ---
> Changes in v2:
> - correct the Fixes tag to 564b026fbd0d
> - renormalize only when another named unit exists
> - preserve the top-end UNK fallback
> - add decimal and binary boundary/neighbor KUnit coverage
> - add non-byte block-size cases that hit the same carry path
>
>  lib/string_helpers.c             | 12 ++++++++++++
>  lib/tests/string_helpers_kunit.c | 25 +++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
>
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index 169eaf5834949..bcabb24fe0dbf 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -121,6 +121,18 @@ int string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
>                 size += 1;
>         }
>
> +       /*
> +        * Renormalize into the next named unit, but preserve the top-end
> +        * UNK fallback. After promotion the value is exactly 1 of the next
> +        * unit, so keep two fractional digits for the usual 1.00 formatting.
> +        */
> +       if (size >= divisor[units_base] && i + 1 < ARRAY_SIZE(units_2)) {
> +               size = 1;
> +               remainder = 0;
> +               i++;
> +               j = 2;
> +       }
> +
>         if (j) {
>                 snprintf(tmp, sizeof(tmp), ".%03u", remainder);
>                 tmp[j+1] = '\0';
> diff --git a/lib/tests/string_helpers_kunit.c b/lib/tests/string_helpers_kunit.c
> index c853046183d24..67822cb48fd15 100644
> --- a/lib/tests/string_helpers_kunit.c
> +++ b/lib/tests/string_helpers_kunit.c
> @@ -558,6 +558,31 @@ static void test_get_size(struct kunit *test)
>         /* weird block sizes */
>         test_string_get_size_one(3000, 1900, "5.70 MB", "5.44 MiB");
>
> +       /* rounding carry into the next unit at the first decimal boundary */
> +       test_string_get_size_one(999499, 1, "999 kB", "976 KiB");
> +       test_string_get_size_one(999500, 1, "1.00 MB", "976 KiB");
> +       test_string_get_size_one(999999, 1, "1.00 MB", "977 KiB");
> +       test_string_get_size_one(1000000, 1, "1.00 MB", "977 KiB");
> +       test_string_get_size_one(1000001, 1, "1.00 MB", "977 KiB");
> +
> +       /* rounding carry into the next unit at the first binary boundary */
> +       test_string_get_size_one(1048063, 1, "1.05 MB", "1023 KiB");
> +       test_string_get_size_one(1048064, 1, "1.05 MB", "1.00 MiB");
> +       test_string_get_size_one(1048575, 1, "1.05 MB", "1.00 MiB");
> +       test_string_get_size_one(1048576, 1, "1.05 MB", "1.00 MiB");
> +       test_string_get_size_one(1048577, 1, "1.05 MB", "1.00 MiB");
> +
> +       /* values already in the next binary unit stay unchanged */
> +       test_string_get_size_one(2097151, 1, "2.10 MB", "2.00 MiB");
> +       test_string_get_size_one(2097152, 1, "2.10 MB", "2.00 MiB");
> +       test_string_get_size_one(2097153, 1, "2.10 MB", "2.00 MiB");
> +
> +       /* non-byte block sizes hit the same carry path */
> +       test_string_get_size_one(4997, 200, "999 kB", "976 KiB");
> +       test_string_get_size_one(4998, 200, "1.00 MB", "976 KiB");
> +       test_string_get_size_one(9981, 105, "1.05 MB", "1023 KiB");
> +       test_string_get_size_one(9982, 105, "1.05 MB", "1.00 MiB");
> +
>         /* huge values */
>         test_string_get_size_one(U64_MAX, 4096, "75.6 ZB", "64.0 ZiB");
>         test_string_get_size_one(4096, U64_MAX, "75.6 ZB", "64.0 ZiB");
> --
> 2.50.1 (Apple Git-155)
>


-- 
With Best Regards,
Andy Shevchenko