Simpler, and no doubt faster.

Change-Id: Idd401918da07a257de365087721e9ff061e6fd07
Reviewed-on: https://go-review.googlesource.com/98759
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>