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

[Johannes Altmanninger]

* 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