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This is still binary comparison.

There are, in general, a number of different sorting algorithms which are optimized for a specific number of elements. In this case, four. It uses five binary comparisons to sort four elements.

You can find other algorithms like this, such as an algorithm that uses seven comparisons to sort five items, or one that uses ten comparisons to sort six items.

Ah, I completely misunderstood what was going on with the quad swap at the start. Rereading it makes more sense. Thanks!

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