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by halomru 3371 days ago
That question is a bit unspecific :D

>NUMBER = atoi(argv[1]);

argv is populated at runtime based on what the OS passed you.

But you are right if you meant that my statement is too strong: you can't do arbitrary loop unrolling. You can jump to a loop that's unrolled once if the number is even, etc.

There are certainly also optimizers that will just output the input without any loop, but that's beyond anything I would expect of a current production compiler.
2 comments
EvilTerran 3371 days ago
Well, you could do arbitrary loop unrolling - with Duff's Device:

https://en.wikipedia.org/wiki/Duffs_device

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gravypod 3371 days ago
If you are going from 0 -> NUMBER and adding one to a variable every iteration, what will the variable's final result be? NUMBER. The compiler can see this and will just do the following:

    s = i = atoi(argv[1]);
Now the loop is gone.

Edit: This will still happen even if you're doing other stuff in there. GCC will attempt to inline and optimize like this. If it is impossible then you will see a loop with most of the stuff factored out of it.

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