Operator

[slate abyss]

Hello everyone ,
I have the question that when ,why we need for bitwize operator how much we should know about them

[queen surge]

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[cyan drift]

there are situation where that's needed for network traffic, some cryptographic things or communication with some other devices

and sometimes also things like checksums

sometimes for parsing binary files or similar

or if you have some sort of (small) bitmap in general or similar

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[slate abyss]

but the question now is t that how much i worked and invest time in them or just skipped them

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[stark swan]

One thing I like to use in Java since there is no negative indexing to get the n-th last element, is to write list.get(list.size() + ~n) which will do exactly that.

[cyan drift]

alternatively list.reversed().get(n) - we don't need that legacy code

[cyan drift]

I wouldn't recommend that in the same way as I wouldn't recommend XOR swapping

code should be readable and doing it with + ~n adds cognitive overhead (people have to think about it to check for correctness)

[stark swan]

I don't use it in production code. Only for Codewars.

[bright mango]

code warrior

https://tenor.com/view/aragorn-lotr-this-day-we-fight-gif-14120757

[stark swan]

I don't trust the jvm to be capable of optimizing this.

[cyan drift]

Premature optimization is the root of all evil. It won't optimize it if it isn't hot either way.

[stark swan]

But I hate garbage.

[cyan drift]

and if it is hot, C2/Graal/Falcon(?) might

• inline the reversed() and get() methods
• remove the allocation/move it to the stack
• extract the calculation
• do it directly in the generated code

Not trusting the JVMto optimize it is not a valid argument unless (all of the following must be true for it to be a valid argument)

• Profiling shows that code is important for performance
• Bemchmarks have been made and they show it is a significant improvement

What makes you think it can optimize list.get(list.size() + ~n) better? Do you have evidence for it?

Also, if it's relevant for performance, are you using List, ArrayList or the array directly as the static type?

[stark swan]

Right, virtual method lookups are already bad. Field accesses to get the size. Ultra bad. I only trust bitarithmetics because that's what CPUs are made for.

[cyan drift]

interface calls (invokeinterface) are often worse than normal virtual lookups (invokevirtual). They can be inlined but it adds additional CPU instructions for checks and it cannot do inlay caching that well.

[stark swan]

https://tenor.com/view/sean-astin-tcb-tin-can-bros-wayward-guide-untrained-eye-gif-21539358

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[queen surge]

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[tribal kayak]

some apis use int bits as boolean which you have to connect with | to get what you want in some cases.

an example for this is specifying multiple foreground service types in android

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