From: Eric Dumazet <eric.dumazet@gmail.com>
To: Jim Gettys <jg@freedesktop.org>
Cc: codel@lists.bufferbloat.net
Subject: Re: [Codel] fp sqrt vis int sqrt?
Date: Fri, 04 May 2012 17:56:33 +0200 [thread overview]
Message-ID: <1336146993.3752.354.camel@edumazet-glaptop> (raw)
In-Reply-To: <4FA3F50D.7080406@freedesktop.org>
On Fri, 2012-05-04 at 11:26 -0400, Jim Gettys wrote:
>
> I suspect there are fully integer implementations kicking around...
> It's just that x86 finally got fast enough FP that doing one multiply in
> floating point beat the alternative.
Anyway we dont need to compute sqrt() at all.
This can be done easily when we do the q->count++, if we hold in
q->sqrt_count the estimated value of sqrt(count)
Ie replace :
q->count++;
by:
q->count++;
n = q->sqrt_count + 1;
if (n * n <= q->count)
q->sqrt_count = n;
A multiply is an acceptable cost.
Of course, you need to reset sqrt_count to 1 when count is reset to 1
next prev parent reply other threads:[~2012-05-04 15:56 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-04 15:11 Dave Taht
2012-05-04 15:14 ` Jim Gettys
2012-05-04 15:19 ` Dave Taht
2012-05-04 15:26 ` Jim Gettys
2012-05-04 15:56 ` Eric Dumazet [this message]
2012-05-04 17:23 ` Dave Taht
2012-05-04 17:43 ` Dave Taht
2012-05-04 17:44 ` Dave Taht
2012-05-04 17:46 ` Dave Taht
2012-05-04 23:42 ` Kathleen Nichols
2012-05-05 0:01 ` Dave Taht
2012-05-04 17:47 ` Eric Dumazet
2012-05-04 18:26 ` Eric Dumazet
2012-05-04 18:39 ` Dave Taht
2012-05-04 18:50 ` Eric Dumazet
2012-05-04 19:04 ` Dave Taht
2012-05-04 19:16 ` Eric Dumazet
2012-05-05 8:14 ` Eric Dumazet
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