On 04/01/2020 00:49, Tom Lane wrote: > Vik Fearing <vik.fear...@2ndquadrant.com> writes: >> On 03/01/2020 20:14, Fabien COELHO wrote: >>> The point of swapping is to a void possibly expensive modulo, but this >>> should be done on absolute values, otherwise it may not achieve its >>> purpose as stated by the comment? >> Ah, true. How widespread are these architectures that need this special >> treatment? Is it really worth handling? > On some older RISC architectures, integer division is really slow, like > slower than floating-point. I'm not sure if that's true on any platform > people still care about though. In recent years, CPU architects have been > able to throw all the transistors they needed at such problems. On a > machine with single-cycle divide, it's likely that the extra > compare-and-branch is a net loss.
OK. > Might be worth checking it on ARM in particular, as being a RISC > architecture that's still popular. I don't know how I would check this. > Also, if we end up having a "numeric" implementation, it absolutely is > worth it for that, because there is nothing cheap about numeric_div. The patch includes a numeric version, and I take care to short-circuit everything I can. > I'd be sort of inclined to have the swap in the other implementations > just to keep the algorithms as much alike as possible. They can't quite be the same behavior because numeric doesn't have the unrepresentable -INT_MIN problem, and integers don't have NaN. -- Vik Fearing
