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From: Juli Mallett <jmallett@FreeBSD.org>
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Subject: Re: ZERO_REGION_SIZE
To: Warner Losh <imp@bsdimp.com>
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Cc: "Jayachandran C." <jchandra@freebsd.org>,
 "freebsd-mips@FreeBSD.org" <mips@freebsd.org>, Alan Cox <alc@rice.edu>
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On Thu, Nov 15, 2012 at 1:07 PM, Warner Losh <imp@bsdimp.com> wrote:

>
> On Nov 15, 2012, at 1:13 PM, Alan Cox wrote:
> > P.S. I would encourage someone with hardware to look into implementing a
> > non-iterative ffs*() using (d)clz.  The MIPS pmap would benefit from
> > this.  Basically, most pmap_enter() calls are doing an ffs*().
>
> ffs finds the first bit set. clz counts the number of leading zeros and
> thus finds the last bit set.  Would a non-iterative fls* be helpful?
>

Right.  And no widespread ctz/ffs MIPS instructions as far as I know.  We
could use pop/dpop on processors that support them to do non-iterative
ffs*, with a few additional instructions, though.