- (y * (K << L) + x) & (-1 << L) => (x & (-1 << L)) + y * (K << L)
- (x + y * (K << L)) & (-1 << L) => (x & (-1 << L)) + y * (K << L)

TEST=unittests
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/811293002

Cr-Commit-Position: refs/heads/master@{#25875}