Re: find_next_bit return type

[Andi Kleen <ak@suse.de>]

On Sun, Aug 01, 2004 at 12:10:26AM -0700, David S. Miller wrote:
> On Sun, 1 Aug 2004 00:02:13 -0700
> Andrew Morton <akpm@osdl.org> wrote:
> 
> > Kind-of.  But it's also cringeworthy to go slinging 8-byte values around
> > when 4-byte values would suffice.  Is it not more efficient to use
> > integers?
> 
> They all go in registers, the same register that could hold the 4-byte
> values too.  There is also no computational cost to doing 64-bit add
> subtract and shift (ie. simple ALU's) compared to 32-bit ones.

Actually at least on Intel EM64T an 64bit sub/add is slower, so it's not
generally true. And 64bit ops generate bigger code on x86-64.

But I still agree with you David that returning long here is better.
Even though I consider it unlikely that anybody will search >4GB 
bitmaps in kernel any time soon (it would be a latency disaster).
But for the usual implementation (find_* subtracting two pointers) 
the function has to do a 64bit subtraction anyways, otherwise
you get a subtle "broken when crossing 4GB boundaries" bug. 
For consistency it is better to have long here.

-Andi