HAMMER_BLOCKMAP_LAYER2_MASK
(((offset) + HAMMER_BLOCKMAP_LAYER2_MASK) & \
~HAMMER_BLOCKMAP_LAYER2_MASK)
((int)(((zone2_offset) & HAMMER_BLOCKMAP_LAYER2_MASK) / \
(((offset) + HAMMER_BLOCKMAP_LAYER2) & ~HAMMER_BLOCKMAP_LAYER2_MASK)