Hash functions aren’t “impenetrable” they’re just math.

I mean, they're both. At a high level it's math, but the individual operations are carefully designed to resist any symbolic manipulation (aka thought) - because that's one step away from an attack.

The point of this post is actually things like x[(I-3)&0x0f]. It’s entirely the same concept as coercion to manipulate index values this way. What’s funny is that void pointer math, function pointer math, void pointers and function pointers in general are typically seen as “beyond the pale” for whatever reason.

If it compiles pretty directly to register pointer math that way, I think it could be justified here. I can't say if it does, or if an alternate approach would too, though.

This portion is simply an manually unrolled loop

Lol, I didn't notice it's a perfect shift. Yeah, that could theoretically be done better. Presumably the justification is because it's a leaf function, and it's hard to guarantee every compilation will unroll it properly.

(lmao these gcc nerds haven’t even heard of Gentoo)

The flag -O3 exists. Or just -funroll-loops. You shouldn't even need -funroll-all-loops in this case, since hashes have a fixed size.

I sound way more competent with the flags than I am here, haha. Does Gentoo use an alternate compiler by default?

Beyond that asking what the memory size of a variable in C is a fools errand because the real answer is “it depends” and “it also depends if someone decided to ignore what it typically depends on (compiler and platform) with some preprocessor fun”.

As I understand it, that's pretty unavoidable if you want C to both compile onto multiple processors and work at a high level the same way on all of them. JavaScript catches shit for doing funny things purely because it was hastily built.

Ditto for fast inverse square root. It's absolutely cursed, but when you're at a certain low level you can't afford pretty anymore. You're feeling the constraint of limited die space and manufacturing steps not too far down the layers of abstraction. Browser scripting, on the other hand, is not low-level.