linux-kernel - Re: [PATCH 02/17] bitops: Add generic parity calculation for u64

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Message-ID: <a8c29dec-6178-4f8f-80f5-aece636c410b@kernel.org>
Date: Thu, 27 Feb 2025 07:38:58 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Yury Norov <yury.norov@...il.com>
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 Yu-Chun Lin <eleanor15x@...il.com>
Subject: Re: [PATCH 02/17] bitops: Add generic parity calculation for u64

On 26. 02. 25, 19:33, Yury Norov wrote:
>> Not in cases where macros are inevitable. I mean, do we need parityXX() for
>> XX in (8, 16, 32, 64) at all? Isn't the parity() above enough for everybody?
> 
> The existing codebase has something like:
> 
>          int ret;
> 
>          ret = i3c_master_get_free_addr(m, last_addr + 1);
>          ret |= parity8(ret) ? 0 : BIT(7)
> 
> So if we'll switch it to a macro like one above, it will become a
> 32-bit parity. It wouldn't be an error because i3c_master_get_free_addr()
> returns an u8 or -ENOMEM, and the error code is checked explicitly.
> 
> But if we decide to go with parity() only, some users will have to
> call it like parity((u8)val) explicitly. Which is not bad actually.

That cast looks ugly -- we apparently need parityXX(). (In this 
particular case we could do parity8(last_addr), but I assume there are 
more cases like this.) Thanks for looking up the case for this.

>> And if not, you can have all those parityXX() as inlines as you suggest, but
>> also provide a macro such as the above to call (optimized) parityXX() as per
>> datatype len.
> 
> Yes, if we need fixed-type parity's, they should all be one-liners
> calling the same macro. Macros or inline functions - no preference for
> me.

-- 
js
suse labs