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A leap year check in three instructions

(hueffner.de)
420 points gnabgib | 1 comments | 15 May 25 21:57 UTC | HN request time: 0.211s | source
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drewg123 ◴[15 May 25 22:47 UTC] No.44000124[source]▶
I tend to be of the opinion that for modern general purpose CPUs in this era, such micro-optimizations are totally unnecessary because modern CPUs are so fast that instructions are almost free.

But do you know what's not free? Memory accesses[1]. So when I'm optimizing things, I focus on making things more cache friendly.

[1] http://gec.di.uminho.pt/discip/minf/ac0102/1000gap_proc-mem_...

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andrepd ◴[15 May 25 23:08 UTC] No.44000266[source]▶
> I tend to be of the opinion that for modern general purpose CPUs in this era, such micro-optimizations are totally unnecessary because modern CPUs are so fast that instructions are almost free.

What does this mean? Free? Optimisations are totally unnecessary because... instructions are free?

The implementation in TFA is probably on the order of 5x more efficient than a naive approach. This is time and energy as well. I don't understand what "free" means in this context.

Calendar operations are performed probably trillions of times every second across all types of computers. If you can make them more time- and energy-efficient, why wouldn't you?

If there's a problem with modern software it's too much bloat, not too much optimisation.

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1. jdlshore ◴[15 May 25 23:15 UTC] No.44000312[source]▶
GP made an important point that you seemed to have missed: in modern architectures, it’s much more important to minimize memory access than to minimize instructions. They weren’t saying optimization isn’t important, they were describing how to optimize on modern systems.