linux-ext4 - binary search in ext4_ext_binsearch

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Date:	Thu, 08 Apr 2010 11:26:16 +0800
From:	minskey <chaohong_guo@...ux.intel.com>
To:	linux-ext4@...r.kernel.org
Subject: binary search in ext4_ext_binsearch_idx()

in ext4_ext_binsearch_idx() routine, there is the following code:

 while (l <= r) {
                m = l + (r - l) / 2;
                if (block < le32_to_cpu(m->ei_block))
                        r = m - 1;
                else
                        l = m + 1;
 }

 path->p_idx = l - 1;

The code always runs logN iterations to get the expected extent,
if 3-way comparison is used, we can save some iterations when 
(block == le32_to_cpu(m->ei_block)) at the first iteration.

some other routines, such as ext4_ext_binsearch() etc, use the
same algorithm (2-way comparison), Is there any special goal ? 

thanks,
-minskey

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