linux-kernel - Re: [PATCH 5/5] Lib: sort.h: replace int size with size

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Date:   Mon, 1 Apr 2019 18:01:51 +0000
From:   Vineet Gupta <vineet.gupta1@...opsys.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "'gregkh@...uxfoundation.org'" <gregkh@...uxfoundation.org>,
        Andrey Abramov <st5pub@...dex.ru>
CC:     George Spelvin <lkml@....org>,
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Subject: Re: [PATCH 5/5] Lib: sort.h: replace int size with size_t size in
 the swap function

On 4/1/19 7:46 AM, David Laight wrote:
> From: gregkh@...uxfoundation.org
>> Sent: 31 March 2019 11:54
> ...
>> Yes, "int" is a very nice variable for "size", you need to explain why
>> it is better to use size_t here please.
> Actually, on x86_64 you probably want 'unsigned int' to avoid the
> compiler having to generate a sign-extending register move if the
> value is ever used in a 64bit expression (eg an address calculation).

Thats likely true for non x86 arches too (for certain on ARC). That is also the
reason I dislike "bool", despite its "software engineering" benefits. Per ARC ABI
(and likely others too) it is signed 8 bits and any use thereof, requires the
compiler to generate an additional EXTB instruction to promote to 32-bit int with
sign extension before using the value.

-Vineet