Re: [PATCH v3 01/16] bitops: Change parity8() return type to bool

H. Peter Anvin
2025-03-07T19:40:33Z

On March 7, 2025 11:36:43 AM PST, David Laight <david.laight.linux@gmail.com> wrote:
>On Fri, 7 Mar 2025 12:42:41 +0100
>Jiri Slaby <jirislaby@kernel.org> wrote:
>
>> On 07. 03. 25, 12:38, Ingo Molnar wrote:
>> >
>> > * Jiri Slaby <jirislaby@kernel.org> wrote:
>> >
>> >> On 06. 03. 25, 17:25, Kuan-Wei Chiu wrote:
>> >>> Change return type to bool for better clarity. Update the kernel doc
>> >>> comment accordingly, including fixing "@value" to "@val" and adjusting
>> >>> examples. Also mark the function with __attribute_const__ to allow
>> >>> potential compiler optimizations.
>> >>>
>> >>> Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
>> >>> Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
>> >>> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
>> >>> ---
>> >>> include/linux/bitops.h | 10 +++++-----
>> >>> 1 file changed, 5 insertions(+), 5 deletions(-)
>> >>>
>> >>> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
>> >>> index c1cb53cf2f0f..44e5765b8bec 100644
>> >>> --- a/include/linux/bitops.h
>> >>> +++ b/include/linux/bitops.h
>> >>> @@ -231,26 +231,26 @@ static inline int get_count_order_long(unsigned long l)
>> >>> /**
>> >>> * parity8 - get the parity of an u8 value
>> >>> - * @value: the value to be examined
>> >>> + * @val: the value to be examined
>> >>> *
>> >>> * Determine the parity of the u8 argument.
>> >>> *
>> >>> * Returns:
>> >>> - * 0 for even parity, 1 for odd parity
>> >>> + * false for even parity, true for odd parity
>> >>
>> >> This occurs somehow inverted to me. When something is in parity means that
>> >> it has equal number of 1s and 0s. I.e. return true for even distribution.
>> >> Dunno what others think? Or perhaps this should be dubbed odd_parity() when
>> >> bool is returned? Then you'd return true for odd.
>> >
>> > OTOH:
>> >
>> > - '0' is an even number and is returned for even parity,
>> > - '1' is an odd number and is returned for odd parity.
>>
>> Yes, that used to make sense for me. For bool/true/false, it no longer
>> does. But as I wrote, it might be only me...
>
>No me as well, I've made the same comment before.
>When reading code I don't want to have to look up a function definition.
>There is even scope for having parity_odd() and parity_even().
>And, with the version that shifts a constant right you want to invert
>the constant!
>
> David
>
>
>
>

Of course, for me, if I saw "parity_odd()" I would think of it as a function that caused the parity to become odd, i.e.

if (!parity(x))
x ^= 1 << 7;