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

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Message-ID: <20250307193643.28065d2d@pumpkin>
Date: Fri, 7 Mar 2025 19:36:43 +0000
From: David Laight <david.laight.linux@...il.com>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>, Kuan-Wei Chiu <visitorckw@...il.com>,
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 Yu-Chun Lin <eleanor15x@...il.com>
Subject: Re: [PATCH v3 01/16] bitops: Change parity8() return type to bool

On Fri, 7 Mar 2025 12:42:41 +0100
Jiri Slaby <jirislaby@...nel.org> wrote:

> On 07. 03. 25, 12:38, Ingo Molnar wrote:
> > 
> > * Jiri Slaby <jirislaby@...nel.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@...il.com>
> >>> Signed-off-by: Yu-Chun Lin <eleanor15x@...il.com>
> >>> Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.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