[PATCH] lib: count_zeros: unify count_{leading,trailing}_zeros()

[PATCH] lib: count_zeros: unify count_{leading,trailing}_zeros()

[Yury Norov]

The 'leading' helper returns BITS_PER_LONG if x == 0, while 'trailing'
one returns COUNT_TRAILING_ZEROS_0, which turns to be -1.

None of the current users explicitly check the returned value for
COUNT_TRAILING_ZEROS_0, except the loongarch, which tests implicitly
for the '>= 0'.

So, align count_trailing_zeros() with the count_leading_zeros(), and
simplify the loongarch handling.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
On top of bitmap-for-next.

 arch/loongarch/kvm/intc/eiointc.c | 4 ++--
 include/linux/count_zeros.h       | 6 ++----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/loongarch/kvm/intc/eiointc.c b/arch/loongarch/kvm/intc/eiointc.c
index d2acb4d09e73..3b5268116727 100644
--- a/arch/loongarch/kvm/intc/eiointc.c
+++ b/arch/loongarch/kvm/intc/eiointc.c
@@ -16,7 +16,7 @@ static void eiointc_set_sw_coreisr(struct loongarch_eiointc *s)
 		ipnum = (s->ipmap >> (irq / 32 * 8)) & 0xff;
 		if (!(s->status & BIT(EIOINTC_ENABLE_INT_ENCODE))) {
 			ipnum = count_trailing_zeros(ipnum);
-			ipnum = (ipnum >= 0 && ipnum < 4) ? ipnum : 0;
+			ipnum = ipnum < 4 ? ipnum : 0;
 		}
 
 		cpuid = ((u8 *)s->coremap)[irq];
@@ -41,7 +41,7 @@ static void eiointc_update_irq(struct loongarch_eiointc *s, int irq, int level)
 	ipnum = (s->ipmap >> (irq / 32 * 8)) & 0xff;
 	if (!(s->status & BIT(EIOINTC_ENABLE_INT_ENCODE))) {
 		ipnum = count_trailing_zeros(ipnum);
-		ipnum = (ipnum >= 0 && ipnum < 4) ? ipnum : 0;
+		ipnum = ipnum < 4 ? ipnum : 0;
 	}
 
 	cpu = s->sw_coremap[irq];
diff --git a/include/linux/count_zeros.h b/include/linux/count_zeros.h
index 5034a30b5c7c..b72ba3faa036 100644
--- a/include/linux/count_zeros.h
+++ b/include/linux/count_zeros.h
@@ -10,8 +10,6 @@
 
 #include <asm/bitops.h>
 
-#define COUNT_TRAILING_ZEROS_0 (-1)
-
 /**
  * count_leading_zeros - Count the number of zeros from the MSB back
  * @x: The value
@@ -38,11 +36,11 @@ static inline int count_leading_zeros(unsigned long x)
  *
  * If the LSB of @x is set, the result is 0.
  * If only the MSB of @x is set, then the result is BITS_PER_LONG-1.
- * If @x is 0 then the result is COUNT_TRAILING_ZEROS_0.
+ * If @x is 0 then the result is BITS_PER_LONG.
  */
 static inline int count_trailing_zeros(unsigned long x)
 {
-	return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0;
+	return x ? __ffs(x) : BITS_PER_LONG;
 }
 
 #endif /* _LINUX_BITOPS_COUNT_ZEROS_H_ */
-- 

Re: [PATCH] lib: count_zeros: unify count_{leading,trailing}_zeros()

[Andy Shevchenko]

On Mon, Mar 23, 2026 at 01:00:32PM -0400, Yury Norov wrote:
> The 'leading' helper returns BITS_PER_LONG if x == 0, while 'trailing'
> one returns COUNT_TRAILING_ZEROS_0, which turns to be -1.
> 
> None of the current users explicitly check the returned value for
> COUNT_TRAILING_ZEROS_0, except the loongarch, which tests implicitly
> for the '>= 0'.
> 
> So, align count_trailing_zeros() with the count_leading_zeros(), and
> simplify the loongarch handling.

Makes sense,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] lib: count_zeros: unify count_{leading,trailing}_zeros()

[Yury Norov]

On Mon, Mar 23, 2026 at 07:10:05PM +0200, Andy Shevchenko wrote:
> On Mon, Mar 23, 2026 at 01:00:32PM -0400, Yury Norov wrote:
> > The 'leading' helper returns BITS_PER_LONG if x == 0, while 'trailing'
> > one returns COUNT_TRAILING_ZEROS_0, which turns to be -1.
> > 
> > None of the current users explicitly check the returned value for
> > COUNT_TRAILING_ZEROS_0, except the loongarch, which tests implicitly
> > for the '>= 0'.
> > 
> > So, align count_trailing_zeros() with the count_leading_zeros(), and
> > simplify the loongarch handling.
> 
> Makes sense,
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

Thanks, Andy. Moving in -next for testing then.