unify sign of int to remove compiler warning
Squashed commit of the following:

commit f85bf29aa54275d9e1c35e56ea252dee1f46fd77
Author: Qiming Sun <osirpt.sun@gmail.com>
Date:   Thu May 8 19:48:32 2014 -0400

    unify sign of int to remove compiler warning

commit 7fd754714d421e5a0d4c6004724715fd0ef34a76
Author: Qiming Sun <osirpt.sun@gmail.com>
Date:   Fri May 2 08:51:29 2014 -0400

    maybe good for L1i cache

commit 0c236edfd80c269e325b243bcf87d352d7bc57e8
Merge: f571a55 6051fda
Author: Qiming Sun <osirpt.sun@gmail.com>
Date:   Fri May 2 08:51:24 2014 -0400

    Merge branch 'master' into optexp
fix bug in test_cint.py caused by optimizer
a bug in optimizer which reads data out of boundary