linux-kernel - Re: Yet more ARM breakage in linux-next

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Message-Id: <200812081650.35014.rusty@rustcorp.com.au>
Date:	Mon, 8 Dec 2008 16:50:34 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <rmk+lkml@....linux.org.uk>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	"Linux/m68k" <linux-m68k@...r.kernel.org>
Subject: Re: Yet more ARM breakage in linux-next

On Monday 08 December 2008 08:20:59 Geert Uytterhoeven wrote:
> On Fri, 5 Dec 2008, Rusty Russell wrote: 
> > +static inline int __fls(int x)
>                  ^^^       ^^^
> Other implementations take `unsigned long' and return `unsigned long'...

It's all over the place, actually.  32 bit archs are especially loose.

I've been toying with the idea of a boottime testsuite for all the
bitops to see who gets them wrong.

> > +static inline int __fls(unsigned long word)
>                  ^^^       ^^^^^^^^^^^^^
> > +{
> > +	return fls(word) - 1;
> > +}
> > +
> 
> ... but this one uses mixed types?

I cut and pasted.  I thought you were 32 bit, so doesn't matter?

> What are the official semantics of __fls()?

Find last bit set in the word, undefined if word is 0.  Returns 0
to BITS_PER_LONG-1.

Cheers,
Rusty.
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