linux-kernel - Re: [PATCH v3 00/16] Introduce and use generic parity16/32/64 helper

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Message-ID: <3dfc81eb-caa1-42fe-8fd6-61101de0ef13@kernel.org>
Date: Fri, 7 Mar 2025 07:57:48 +0100
From: Jiri Slaby <jirislaby@...nel.org>
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 Yu-Chun Lin <eleanor15x@...il.com>
Subject: Re: [PATCH v3 00/16] Introduce and use generic parity16/32/64 helper

On 06. 03. 25, 17:25, Kuan-Wei Chiu wrote:
> Several parts of the kernel contain redundant implementations of parity
> calculations for 16/32/64-bit values. Introduces generic
> parity16/32/64() helpers in bitops.h, providing a standardized
> and optimized implementation.
> 
> Subsequent patches refactor various kernel components to replace
> open-coded parity calculations with the new helpers, reducing code
> duplication and improving maintainability.
> 
> 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>
> ---
> In v3, I use parityXX() instead of the parity() macro since the
> parity() macro may generate suboptimal code and requires special hacks
> to make GCC happy. If anyone still prefers a single parity() macro,
> please let me know.

What is suboptimal and where exactly it matters? Have you actually 
measured it?

> Additionally, I changed parityXX() << y users to !!parityXX() << y
> because, unlike C++, C does not guarantee that true casts to int as 1.

How comes? ANSI C99 exactly states:
===
true
which expands to the integer constant 1,
===

thanks,
-- 
js
suse labs