So reading through the salsa20 implementation for the crypto library for go-lang, I noticed something interesting. Specifically this portion. It looks like something I would expect from someone learning programming. They took 80 lines of code of what could have been easily done using an array and iteration. Looking up other implementations I found this unofficial one, which does use iteration. Looking at other they all choose to do this portion using a loop. But these are not the official ones. So why doesn't the official one use the more terse, but equivalent way?
My question really is, is there some security benefit to doing things without an extra array and loop? Is it speed? Is there some attack when you have an extra array and loop?