NODE_PRESENT
assert(thrash_state[index] != NODE_PRESENT);
thrash_state[index] = NODE_PRESENT;
assert(thrash_state[index] == NODE_PRESENT);
if (thrash_state[index] != NODE_PRESENT) {
assert(thrash_state[index] != NODE_PRESENT);
thrash_state[index] = NODE_PRESENT;
case NODE_PRESENT: