These are implemented in asm, they're just not inlined.
Open questions are:
* Should I just inline them? They're.. big, but it seems as though this needs violates the #[inline(always)] gaurantees the others make.
* Does something (llvm?) provide these as intrinsics? The structure of this code suggests that we could be hoisting off something else, instead of flagrantly ignoring it like we do for power and mips.
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