linux-kernel - RE: [PATCH] staging: pi433: Use div64_u64 instead of do

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Message-ID: <e2ec77060cc84a33b49d5fd11d7867f6@AcuMS.aculab.com>
Date:   Wed, 19 Oct 2022 10:31:17 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kang Minchul' <tegongkang@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
CC:     Dan Carpenter <error27@...il.com>,
        Sidong Yang <realwakka@...il.com>,
        "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] staging: pi433: Use div64_u64 instead of do_div

From: Kang Minchul
> Sent: 19 October 2022 10:40
> 
> This commit removes warning generated by cocci as follows:
> 
> do_div() does a 64-by-32 division, please consider using div64_u64 instead.
> 
> Using div64_u64 instead of do_div can avoid potential truncation.

Cocci is lying to you.

do_div() exists because a 64 by 32 bit divide is significantly
faster than a 64 by 64 divide.
This is particularly true on 32bit cpu, but is also true on
Intel x86_64 bit cpu.

So unless the result might actually be larger than 32 bits
(which requires code analysis) then do_div() is correct.

	David

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