[mistercow]

The other person who replied may have already cleared this up for you, but the two conditions you listed mean very different things. The first means “if the next node is not adjacent in memory”, while the second means “if there is no next node.

[mjevans]

This is crucially followed by the node++ instruction. As noted elsewhere, this increases the value of the <pointer to 'a node'> by the <sizeof 'a node'>, thereby allowing the CPU to execute at the faster of it's memory prefetch / the speculation of the inner code loop execution speed, for as long as the sequence of list nodes is contiguous and sequential.