linux-kernel - Re: [RFC] include/linux/make_type.h: Helpers for making u16/u32/u64 values

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Message-ID: <Zcz7aXE6bVhJGEyw@smile.fi.intel.com>
Date: Wed, 14 Feb 2024 19:42:01 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Alexey Dobriyan <adobriyan@...il.com>
Cc: Michal Wajdeczko <michal.wajdeczko@...el.com>,
	linux-kernel@...r.kernel.org, Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Jani Nikula <jani.nikula@...el.com>
Subject: Re: [RFC] include/linux/make_type.h: Helpers for making u16/u32/u64
 values

On Wed, Feb 14, 2024 at 08:39:35PM +0300, Alexey Dobriyan wrote:
> On Wed, Feb 14, 2024 at 07:32:10PM +0200, Andy Shevchenko wrote:
> > On Wed, Feb 14, 2024 at 08:20:55PM +0300, Alexey Dobriyan wrote:

..

> > > Secondly,
> > > 
> > > 	#define make_u64(hi__, lo__)  ((u64)(hi__) << 32 | (u32)(lo__))
> > > 
> > > doesn't truncate hi, why?
> > 
> > Because it's not needed (the whole point AFAIU is to override promotion
> > to a _signed_ type (int) and here it makes no difference)?
> 
> Well,
> 
> 	make_u64((u64)-1, 0)
> 
> will return (u64)-1 unlike

How? It's shifted by 32 bits. Am I missing something?

> BTW, I'm for truncation, but it should be done everywhere.

I'm not against this.

-- 
With Best Regards,
Andy Shevchenko