linux-kernel - Re: [PATCH 1/5] lib/sort: Make swap functions more generic

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Message-Id: <201903141009.x2EA9q1Z025888@sdf.org>
Date:   Thu, 14 Mar 2019 10:09:52 GMT
From:   George Spelvin <lkml@....org>
To:     13@....org, andriy.shevchenko@...ux.intel.com, lkml@....org,
        st5pub@...dex.ru
Cc:     akpm@...ux-foundation.org, daniel.wagner@...mens.com,
        dchinner@...hat.com, don.mullis@...il.com, geert@...ux-m68k.org,
        linux-kernel@...r.kernel.org, linux@...musvillemoes.dk
Subject: Re: [PATCH 1/5] lib/sort: Make swap functions more generic

On Sat, 09 Mar 2019 at 23:19:49 +0300, Andrey Abramov wrote:
>> Although I'm thinking of:
>>
>> static bool __attribute_const__
>> is_aligned(const void *base, size_t size, unsigned char align)
>> {
>> 	unsigned char lsbits = (unsigned char)size;
>>
>> 	(void)base;
>> #ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
>> 	lsbits |= (unsigned char)(uintptr_t)base;
>> #endif
>> 	return (lsbits & (align - 1)) == 0;
>> }
>>
>> Any preference?
> I think it would be better.

>> I find "u32s" confusing; I keep reading the "s" as "signed" rather
>> than a plural.
>>
>> How about one of:
>> swap_bytes / swap_ints / swap_longs
>> swap_1 / swap_4 / swap_8
>
> In my opinion "swap_bytes / swap_ints / swap_longs" are the most readable.


On Thu, 14 Mar 2019 at 11:29:58 +0200, Andy Shevchenko wrote:
> On Sat, Mar 09, 2019 at 03:53:41PM +0000, lkml@....org wrote:
>> static bool __attribute_const__
>> is_aligned(const void *base, size_t size, unsigned char align)
>> {
>> 	unsigned char lsbits = (unsigned char)size;
>> #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
>> 	(void)base;
>> #else
>> 	lsbits |= (unsigned char)(uintptr_t)base;
>> #endif
>> 	return (lsbits & (align - 1)) == 0;
>> }
>
>> Any preference?
>
> This one looks better in a sense we don't suppress the warnings when it's
> not needed.

>>> For such primitives that operates on top of an arrays we usually
>>> append 's' to the name. Currently the name is misleading.
>>> 
>>> Perhaps u32s_swap().
>> 
>> I don't worry much about the naming of static helper functions.
>> If they were exported, it would be a whole lot more important!
>> 
>> I find "u32s" confusing; I keep reading the "s" as "signed" rather
>> than a plural.
>
> For signedness we use prefixes; for plural, suffixes. I don't see the point of
> confusion. And this is in use in kernel a lot.
>
>> How about one of:
>> swap_bytes / swap_ints / swap_longs
>> swap_1 / swap_4 / swap_8
>
> longs are ambiguous, so I would prefer bit-sized types.

I already implemented Andrey's suggestions, which were the exact
opposite of yours.

Pistols at dawn?


>>>> +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
>>> 
>>> Why #ifdef is better than if (IS_ENABLED()) ?
>> 
>> Because CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is bool and not
>> tristate.  IS_ENABLED tests for 'y' or 'm' but we don't need it
>> for something that's only on or off.
>
> There is IS_BUILTIN(), though it's a common practice to use IS_ENABLED()
> even for boolean options (I think because of naming of the macro).

Well, as I said earlier, #ifdef is the most common form in the kernel.
It's also the shortest to write, and I like the fact that it slightly
simpler.  (Admittedly, "IS_ENABLED" does not take a lot of brain power
to interpret, but it *is* one more macro that might be hiding magic.)

So I'm not inclined to change it without a substantial reason.