bug#35291: [PATCH] split: fix incorrect suffix length computation

[Johannes Altmanninger]

Does anyone have time to review this? I think it's an evident bug.
I can try to improve the clarity of the patch if needed.

On Mon, Apr 15, 2019 at 08:05:34PM +0200, Johannes Altmanninger wrote:
> * src/split.c (set_suffix_length): suffix_needed is now computed
> to be the equivalent of ceil(log(n_units_end) / log(alphabet_len)).
> Previously, it would give the floor of above logarithm if the number
> of units is divisible by the length of the alphabet.
> * tests/split/suffix-auto-length.sh: Add test demonstrating the problem.
> ---
> 
> Hi,
> 
> This should be a fairly straightforward fix.  It seems like it has been
> discovered in 2015 [1] (look for "multiple of 10") but the bug fixed at that
> time was a different one. I am not aware of any open bug for this.
> 
> Let me know if I am missing something.
> 
> Thanks,
> Johannes
> 
> [1] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=20511
> 
>  src/split.c                       | 11 ++++++-----
>  tests/split/suffix-auto-length.sh |  4 ++++
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/src/split.c b/src/split.c
> index 30fdb4462..22b645fc9 100644
> --- a/src/split.c
> +++ b/src/split.c
> @@ -191,13 +191,14 @@ set_suffix_length (uintmax_t n_units, enum Split_type 
> split_type)
>                if (n_start < n_units)
>                  n_units_end += n_start;
>              }
> -
>          }
>        size_t alphabet_len = strlen (suffix_alphabet);
> -      bool alphabet_slop = (n_units_end % alphabet_len) != 0;
> -      while (n_units_end /= alphabet_len)
> -        suffix_needed++;
> -      suffix_needed += alphabet_slop;
> +      uintmax_t max_units = 1;
> +      while (max_units < n_units_end)
> +        {
> +          suffix_needed++;
> +          max_units *= alphabet_len;
> +        }
>        suffix_auto = false;
>      }
>  
> diff --git a/tests/split/suffix-auto-length.sh 
> b/tests/split/suffix-auto-length.sh
> index e5594d878..691c31ad4 100755
> --- a/tests/split/suffix-auto-length.sh
> +++ b/tests/split/suffix-auto-length.sh
> @@ -50,4 +50,8 @@ rm -f x*
>  # as that would result in an incorrect order for the total output file set
>  returns_ 1 split --numeric-suffixes=100 --number=r/100 file.in || fail=1
>  
> +truncate -s0 file.in || framework_failure_
> +
> +returns_ 0 split --numeric-suffixes --number=r/110 file.in || fail=1
> +
>  Exit $fail
> -- 
> 2.21.0
>