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

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Date: Wed, 14 Feb 2024 20:39:35 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.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 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

	make_u16((u64)-1, 0)

which will return 0xff00.
BTW, I'm for truncation, but it should be done everywhere.

Thirdly, there were no users posted.