count_leading_zeros() is based on fls(), which is defined for x == 0,
contrary to ffs() family. The comment in crypto/mpi erroneously states
that the function may return undef in such case.

Fix the comment together with the outdated function signature, and now
that COUNT_LEADING_ZEROS_0 is not referenced in the codebase, get rid of
it too.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
v1: https://lore.kernel.org/all/20260310211021.95362-1-ynorov@nvidia.com/
v2: cleanup trailing whitespaces, tweak comments (Andy)

 include/linux/count_zeros.h | 4 +---
 lib/crypto/mpi/longlong.h   | 8 ++++----
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/include/linux/count_zeros.h b/include/linux/count_zeros.h
index 5b8ff5ac660d..4e5680327ece 100644
--- a/include/linux/count_zeros.h
+++ b/include/linux/count_zeros.h
@@ -18,7 +18,7 @@
  *
  * If the MSB of @x is set, the result is 0.
  * If only the LSB of @x is set, then the result is BITS_PER_LONG-1.
- * If @x is 0 then the result is COUNT_LEADING_ZEROS_0.
+ * If @x is 0 then the result is BITS_PER_LONG.
  */
 static inline int count_leading_zeros(unsigned long x)
 {
@@ -28,8 +28,6 @@ static inline int count_leading_zeros(unsigned long x)
 		return BITS_PER_LONG - fls64(x);
 }
 
-#define COUNT_LEADING_ZEROS_0 BITS_PER_LONG
-
 /**
  * count_trailing_zeros - Count the number of zeros from the LSB forwards
  * @x: The value
diff --git a/lib/crypto/mpi/longlong.h b/lib/crypto/mpi/longlong.h
index b6fa1d08fb55..a5ef41c8f85d 100644
--- a/lib/crypto/mpi/longlong.h
+++ b/lib/crypto/mpi/longlong.h
@@ -66,12 +66,12 @@
  * denominator).  Like udiv_qrnnd but the numbers are signed.  The quotient
  * is rounded towards 0.
  *
- * 5) count_leading_zeros(count, x) counts the number of zero-bits from the
+ * 5) count_leading_zeros(x) counts the number of zero-bits from the
  * msb to the first non-zero bit in the UWtype X.  This is the number of
- * steps X needs to be shifted left to set the msb.  Undefined for X == 0,
- * unless the symbol COUNT_LEADING_ZEROS_0 is defined to some value.
+ * steps X needs to be shifted left to set the msb.
+ * count_leading_zeros(0) == BITS_PER_LONG
  *
- * 6) count_trailing_zeros(count, x) like count_leading_zeros, but counts
+ * 6) count_trailing_zeros() like count_leading_zeros(), but counts
  * from the least significant end.
  *
  * 7) add_ssaaaa(high_sum, low_sum, high_addend_1, low_addend_1,
-- 
2.43.0

On Thu, Mar 12, 2026 at 12:11:32PM -0400, Yury Norov wrote:
> count_leading_zeros() is based on fls(), which is defined for x == 0,
> contrary to ffs() family. The comment in crypto/mpi erroneously states
> that the function may return undef in such case.
> 
> Fix the comment together with the outdated function signature, and now
> that COUNT_LEADING_ZEROS_0 is not referenced in the codebase, get rid of
> it too.

FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko

On Thu, Mar 12, 2026 at 06:17:48PM +0200, Andy Shevchenko wrote:
> On Thu, Mar 12, 2026 at 12:11:32PM -0400, Yury Norov wrote:
> > count_leading_zeros() is based on fls(), which is defined for x == 0,
> > contrary to ffs() family. The comment in crypto/mpi erroneously states
> > that the function may return undef in such case.
> > 
> > Fix the comment together with the outdated function signature, and now
> > that COUNT_LEADING_ZEROS_0 is not referenced in the codebase, get rid of
> > it too.
> 
> FWIW,
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Thanks, it worth!

Applied for testing in -next.

Thanks,
Yury

On Thu, Mar 12, 2026 at 12:34:39PM -0400, Yury Norov wrote:
> On Thu, Mar 12, 2026 at 06:17:48PM +0200, Andy Shevchenko wrote:
> > On Thu, Mar 12, 2026 at 12:11:32PM -0400, Yury Norov wrote:
> > > count_leading_zeros() is based on fls(), which is defined for x == 0,
> > > contrary to ffs() family. The comment in crypto/mpi erroneously states
> > > that the function may return undef in such case.
> > > 
> > > Fix the comment together with the outdated function signature, and now
> > > that COUNT_LEADING_ZEROS_0 is not referenced in the codebase, get rid of
> > > it too.
> > 
> > FWIW,
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> 
> Thanks, it worth!
> 
> Applied for testing in -next.
> 
> Thanks,
> Yury

Acked-by: Eric Biggers <ebiggers@kernel.org>

- Eric