linux-kernel - Re: [PATCH 1/1] vsprintf: optimize decimal conversion (again)

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Message-ID: <4F70CFA4.5020503@zytor.com>
Date:	Mon, 26 Mar 2012 13:20:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Denys Vlasenko <vda.linux@...glemail.com>,
	linux-kernel@...r.kernel.org, Douglas W Jones <jones@...uiowa.edu>,
	Michal Nazarewicz <mnazarewicz@...gle.com>
Subject: Re: [PATCH 1/1] vsprintf: optimize decimal conversion (again)

On 03/26/2012 01:13 PM, Andrew Morton wrote:
> On Mon, 26 Mar 2012 21:56:38 +0200
> Denys Vlasenko <vda.linux@...glemail.com> wrote:
> 
>>>> +#if BITS_PER_LONG != 32 || (~(0ULL)>>1) != ((1ULL<<63)-1)
>>>
>>> What's this for?
>>
>> The second check should be just BITS_PER_LONG_LONG != 64,
>> but we don't have BITS_PER_LONG_LONG.
> 
> So let's add BITS_PER_LONG_LONG rather than hacking around its absence!

First of all, the #if is wrong: the preprocessor doesn't support data
types and does all arithmetic at (u)intmax_t precision.

As far as BITS_PER_LONG_LONG, there are tons of places in the kernel
which already require that long long is exactly 64 bits.  That may or
may not be a good thing, but for right now one could simply:

#define BITS_PER_LONG_LONG 64

	-hpa

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