Re: [PATCH] x86: generic versions of find_first_(zero_)bit, convert i386

[Alexander van Heukelum]

On Sun, 6 Apr 2008 13:22:58 -0700 (PDT), "dean gaudet" <dean@xxxxxxxxxx>
said:
> On Sun, 6 Apr 2008, Alexander van Heukelum wrote:
> 
> > The current generic implementation of ffz is O(lg(n)) already
> 
> it's O(lg(n)) time... the operations all depend on each other.
> 
> the implementation i pointed to is O(lg(n)) code space... and the time 
> depends on how parallel the machine is, they're not dependent on each 
> other.

Indeed. The worst dependencies are in the sum of all the partial
results in this implementation. And addition is associative, so
partial results can be written as ((a+b)+(c+d))+(e+f). Assuming
perfect parallel execution this would lead to O(ln(ln(n))). Good.

Care to implement ffs and __ffs like this?

Greetings,
    Alexander

> -dean
-- 
  Alexander van Heukelum
  heukelum@xxxxxxxxxxx

-- 
http://www.fastmail.fm - The professional email service

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/