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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: 0.21s | 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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1. GuB-42 ◴[15 May 25 23:39 UTC] No.44000430[source]▶
Integer division (and modulo) is not cheap on most CPUs. Along with memory access and branch prediction, it is something worth optimizing for.

And since you are talking about memory. Code also goes in memory. Shorter code is more cache friendly.

I don't see a use case where it matters for this particular application (it doesn't mean there isn't) but well targeted micro-optimizations absolutely matter.