linux-kernel - Re: [PATCH 2/3] lib: vsprintf: optimised put

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Date:	Fri, 6 Aug 2010 09:35:26 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	linux-kernel@...r.kernel.org, m.nazarewicz@...sung.com,
	"Douglas W. Jones" <jones@...uiowa.edu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] lib: vsprintf: optimised put_dec() for 32-bit machines

On Friday 06 August 2010 09:08, Michal Nazarewicz wrote:
> >> +static noinline_for_stack
> >> +char *put_dec(char *buf, unsigned long long n)
> >> +{
> >> +	uint32_t d3, d2, d1, q;
> >> +
> >> +	if (!n) {
> >> +		*buf++ = '0';
> >> +		return buf;
> >> +	}
> >> +
> >> +	d1  = (n >> 16) & 0xFFFF;
> >> +	d2  = (n >> 32) & 0xFFFF;
> >> +	d3  = (n >> 48) & 0xFFFF;
> >
> > Are you assuming that sizeof(long long) == 8, always?
> 
> Well...  yes.  C requires long long to be at least 64-bit and I don't
> see it being larger in any foreseeable feature.

"640k will be enough for everybody"?

> Wouldn't it be enough to put a static assert here?

I'd prefer the code which works with arbitrarily wide long long.
If needed, use

if (sizeof(long long) == 8)
	64-bit code
else
	generic code

-- 
vda
 
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