Use rsqrt in kernel codes.
Use rsqrt in kernel codes.

hvy/chainer,jnishi/chainer,ktnyt/chainer,keisuke-umezawa/chainer,jnishi/chainer,cupy/cupy,chainer/chainer,anaruse/chainer,rezoo/chainer,ktnyt/chainer,cupy/cupy,okuta/chainer,ysekky/chainer,jnishi/chainer,ktnyt/chainer,hvy/chainer,hvy/chainer,cupy/cupy,chainer/chainer,kiyukuta/chainer,niboshi/chainer,hvy/chainer,wkentaro/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,tkerola/chainer,wkentaro/chainer,ronekko/chainer,niboshi/chainer,delta2323/chainer,wkentaro/chainer,chainer/chainer,kashif/chainer,aonotas/chainer,okuta/chainer,cupy/cupy,pfnet/chainer,niboshi/chainer,chainer/chainer,jnishi/chainer,ktnyt/chainer,okuta/chainer,wkentaro/chainer,niboshi/chainer,keisuke-umezawa/chainer,okuta/chainer