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From: Jim Rees <rees@umich.edu>
To: Benny Halevy <bhalevy@tonian.com>
Cc: Boaz Harrosh <bharrosh@panasas.com>,
	fanchaoting <fanchaoting@cn.fujitsu.com>,
	Benny Halevy <benny@tonian.com>,
	linux-nfs@vger.kernel.org
Subject: Re: [PATCH] fix do_xor_speed 64-bit devision issue on 32-bits arch
Date: Sun, 25 Dec 2011 08:54:43 -0500	[thread overview]
Message-ID: <20111225135443.GA19491@umich.edu> (raw)
In-Reply-To: <4EF6B516.5070609@tonian.com>

Benny Halevy wrote:

  > speed = do_div(BENCH_SIZE, 1024) * count * do_div(NSEC_PER_SEC, ns_end);
  > 
  > This might not be exactly right because it changes the operator precedence,
  > but it should eliminate the calls to __udivdi3.
  
  Hmm, you mean execution order? (which you do not)
  C (and fortunately gcc too :) treats multiplication and division with the
  same priority and executes them from left to right...

Yes, execution order.  The original code executes left-to-right, my code
executes the divisions first.

But I wouldn't blindly apply this without understanding what's going on
here.  I thought the -fno-tree-scev-cprop compiler flag was supposed to
emit division code instead of calling into a library.

  reply	other threads:[~2011-12-25 13:54 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-07 14:08 [PATCH] fix do_xor_speed 64-bit devision issue on 32-bits arch Benny Halevy
2011-12-23  6:41 ` fanchaoting
2011-12-23 13:25   ` Jim Rees
2011-12-25  5:31     ` Benny Halevy
2011-12-25 13:54       ` Jim Rees [this message]
2011-12-25 15:25       ` Boaz Harrosh
2011-12-25 15:57         ` Jim Rees
2011-12-26  7:11         ` Benny Halevy

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