Subject: bug#16544: Optimazation for is_mb_middle

From: Norihiro Tanaka <[email-masked]>
Date: Wed, 29 Jan 2014 00:35:54 +0900

I'm sorry that I don't test the patch sufficiently.

I fixed several bugs in the patch.  In addition to the patch, I attach
the results of the compile and the performance test.