linux-kernel - Re: [PATCH V2 04/19] math64: Tidy mul_u64_u32

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Date: Wed, 24 Apr 2024 17:11:33 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org
Subject: Re: [PATCH V2 04/19] math64: Tidy mul_u64_u32_shr()

On Mon, Mar 25, 2024 at 08:40:08AM +0200, Adrian Hunter wrote:
> Put together declaration and initialization of local variables.
> 
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---

Nothing wrong with this patch, but it is highly unlikely this code is
actually tested much. Most (sane) architectures will use the __int128
version.

>  include/linux/math64.h | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/include/linux/math64.h b/include/linux/math64.h
> index bf74478926d4..fd13622b2056 100644
> --- a/include/linux/math64.h
> +++ b/include/linux/math64.h
> @@ -179,16 +179,12 @@ static __always_inline u64 mul_u64_u64_shr(u64 a, u64 mul, unsigned int shift)
>  #ifndef mul_u64_u32_shr
>  static __always_inline u64 mul_u64_u32_shr(u64 a, u32 mul, unsigned int shift)
>  {
> -	u32 ah, al;
> +	u32 ah = a >> 32, al = a;
>  	u64 ret;
>  
> -	al = a;
> -	ah = a >> 32;
> -
>  	ret = mul_u32_u32(al, mul) >> shift;
>  	if (ah)
>  		ret += mul_u32_u32(ah, mul) << (32 - shift);
> -
>  	return ret;
>  }
>  #endif /* mul_u64_u32_shr */
> -- 
> 2.34.1
>